Anion exchange membrane and method of manufacturing and using same

Abstract

The present invention relates to anion exchange membranes (AEMs) having multiblock copolymers containing hydrophilic norbornene-based monomers and hydrophobic alkene-based or norbornene-based monomers. The hydrophilic norbornene-based monomers have one or more cationic head groups, such as quaternary ammonium ions, which can optionally be crosslinked with a crosslinking agent to increase the structural stability of the polymer. These AEMs can be used in electrochemical devices, such as fuel cells. [Selected Figure] Figure 1A

Description

[Technical Field]

[0001] Priority statement This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62 / 648,508, filed March 27, 2018, and U.S. Provisional Patent Application No. 62 / 764,912, filed August 16, 2018, both of which are incorporated by reference in their entireties.

[0002] Statement of funded research This invention was made with government support under Grant No. DE-AR0000769 awarded by the United States Department of Energy. The government has certain rights in this invention.

[0003] The present invention is directed to the preparation of anion exchange membranes made from multi-block copolymers and their use in electronic and electrochemical devices. [Background technology]

[0004] Alkaline anion-exchange membrane electrochemical devices, such as anion exchange membrane fuel cells (AEMFCs), electrolyzers, and flow batteries, have attracted increasing interest due to their non-platinum catalyst and facile reaction kinetics (Pan, J. et al., Chem. Mater. 2017, 29, 5321-5330; Gottesfeld, S. et al., J. Power Sources 2017, 375, 170-184; Dekel, DR et al., J. Power Sources 2018, 375, 158-169). Solid anion-exchange membranes (AEMs) are a crucial component of electrochemical devices. AEMs are an area of ​​active research, and some significant advances have been made in recent years (Ponce-Gonzalez, J. et al., Energy Environ. Sci. 2016, 9, 3724-3735; Varcoe, JR et al., Energy Environ. Sci. 2014, 7, 3135-3191; Pan, ZF et al., Prog. Energy Combust. 2018, 66, 141-175; Arges, CG et al., ACS Appl. Energy Mater. 2018, 1, 2991-3012). The requirements for AEMs include (i) high ionic conductivity, (ii) chemical and thermal stability at high pH, ​​and (iii) mechanical toughness and durability suitable for device fabrication and operation (Sun, Z. et al., ChemSusChem 2017, 11, 58-70; Pan, J. et al., Acc. Chem. Res. 2012, 45, 473-481).However, optimizing all of their properties can be difficult because polar portions of the polymer backbone or other moieties in the polymer structure have created issues with long-term alkaline stability, especially at high pH (Nunez, SA et al., Chem. Mater. 2016, 28, 2589-2598; Xue, J. et al., J. Mater. Chem. 2018, 6, 11317-11326; Liu, D. et al., J. Mater. Chem. 2018, 6, 10879-10890).

[0005] A common strategy to increase ionic conductivity is to synthesize polymers with high ion exchange capacity (IEC). However, this can lead to high water uptake (WU), which often reduces the mechanical toughness of the polymer and floods the ion-conducting channels (Pan, J. et al., Energy Environ. Sci. 2014, 7, 354-360; Hossain, MM et al., J. Power Sources 2018, 390, 234-241). Crosslinking is a simple way to limit WU and membrane swelling. However, a high degree of crosslinking can hinder the flexibility of the polymer, reduce ion mobility, and result in poor mechanical properties (Lin, CX et al., J. Membr. Sci. 2017, 539, 24-33; Lee, KH et al., Energy Environ. Sci. 2017, 10, 275-285; Wang, J. et al., J. Membr. Sci. 2014, 459, 86-95). The long-term alkaline stability of AEMs is a critical issue for anionic devices. Increasing the device operating temperature is highly desirable as it improves electrokinetics, and high water vapor pressure aids in water management, making WU less of a problem; however, high temperatures accelerate nucleophilic hydroxide ion attack (Fujimoto, C. et al., J. Membr. Sci. 2012, 423, 438-449). Benzyl-linked trimethylammonium is known to be an unstable means of cation binding (i.e., a fixed quaternary ammonium cation). The electron-withdrawing nature of the aromatic ring makes the benzyl-linked quaternary ammonium cation susceptible to nucleophilic attack (Arges, C. G. et al., Proc. Natl. Acad. Sci. USA 2013, 110, 2490-2495).To mitigate this degradation, long alkyl tethers have been used to replace the methylene groups between the polymer backbone and the fixed cationic head group (Guo, D. et al., ACS Appl. Mater. Interfaces 2016, 8, 25279-88; Lee, W.-H. et al., ACS Macro Lett. 2017, 6, 566-570; Dang, H.-S. et al., J. Mater. Chem. A 2016, 4, 11924-11938). Furthermore, electron-withdrawing groups, such as sulfones and aryl ethers, have stability issues in alkaline solutions at typical device operating temperatures (e.g., 80 °C). Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a significant need in the art to develop polymers that overcome the above-mentioned drawbacks and exhibit desirable physical properties that enable their application in electronic devices. [Means for solving the problem]

[0007] The anion-exchange membranes (AEMs) of the present invention are AEMs composed of an all-hydrocarbon backbone with long alkyl-tethered side chains containing anchoring cationic head groups. The polymers exhibit suitable chemical stability and physical characteristics desirable for use in electronic devices.

[0008] In particular, one aspect of the present invention relates to multi-block copolymers comprising one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks.

[0009] One aspect of the present invention relates to a multi-block copolymer comprising one or more hydrophilic blocks and one or more hydrophobic blocks based on norbornene, for example, the one or more hydrophobic blocks are norbornene-based hydrophobic blocks comprising one or more hydrophobic monomers having a structure represented by formula (I):

[0010] [ka] where: R1 is a branched or unbranched saturated C1-C20 alkyl chain or halogenated alkyl chain; n is an integer from 1 to about 1,000.

[0011] In another example, the one or more hydrophobic blocks are alkene-based hydrophobic blocks comprising one or more hydrophobic monomers having a structure represented by formula (II):

[0012] [ka] where: R2 and R3 are independently selected from H, a bond (it is unclear what is meant by a bond), and a branched or unbranched saturated C1-C20 alkyl or halogenated alkyl chain; x is an integer of about 10 to about 1,000.

[0013] Examples of the one or more hydrophilic blocks include one or more hydrophilic monomers having a structure represented by formula (III):

[0014] [ka] where: R4 is a branched or unbranched saturated C2-C20 alkyl chain bearing one or more cationic head groups; m is an integer of about 10 to about 1,000.

[0015] Another aspect of the present invention relates to anion-exchange membranes (AEMs) comprising the multi-block copolymers of the present invention. For example, the AEMs of the present invention may comprise a structure represented by the following formula:

[0016] [ka] where: R4 is a branched or unbranched saturated C1-C20 alkyl chain; R1 is a branched or unbranched saturated C2-C20 alkyl chain; X is a cationic head group containing a cationic charged heteroatom (e.g., + N(CH3)2), R5 is a crosslinker containing a branched or unbranched saturated C2-C10 alkyl chain; n, m, o, and p are integers independently selected from about 10 to about 1,000.

[0017] Another aspect of the present invention relates to methods for making the multi-block copolymers of the present invention, for example, by vinyl addition polymerization or ring opening metathesis polymerization (ROMP).

[0018] Another aspect of the present invention relates to a method of making a crosslinked multi-block copolymer comprising crosslinking one or more hydrophilic blocks in the multi-block copolymer of the present invention with one or more crosslinking agents.

[0019] Another aspect of the present invention relates to devices, such as electrochemical devices, including fuel cells, electrolyzers, and redox flow batteries, comprising the multiblock copolymers and / or anion exchange membranes (AEMs) of the present invention.

[0020] Although aspects of the invention may be described and claimed in particular statutory classifications, such as system statutory classifications, this is merely for convenience, and one of ordinary skill in the art will understand that each aspect of the invention may be described and claimed in any statutory classification. Unless expressly stated otherwise, it is in no way intended that any method or aspect described herein be construed as requiring its steps to be performed in a particular order. Thus, unless a method claim specifically recites in the claims or description that its steps are to be limited to a particular order, it is in no way intended that order be inferred. This holds true regardless of any possible implied principles of interpretation, including questions of logic regarding the arrangement or operational flow of steps, apparent meaning derived from grammatical structure or punctuation, or the number or type of aspects described herein. [Brief explanation of the drawings]

[0021] [Figure 1A] FIG. 1A shows the 1H NMR spectrum of the tetrablock PNB-X54-Y46 in CDCl3. [Figure 1B] FIG. 1B shows the AEM films of PNB-X70-Y30-PFTE and PNB-X70-Y30-PO. [Figure 2] FIG. 2 shows the 1H NMR spectrum of the tetrablock PNB-X74-Y26 in CDCl3. [Figure 3] FIG. 3 shows the H NMR spectrum of the tetrablock PNB-X70-Y30 in CDCl3. [Figure 4] FIG. 4 shows the 1H NMR spectrum of the tetrablock PNB-X67-Y33 in CDCl3. [Figure 5] FIG. 5 shows the 1H NMR spectrum of the tetrablock PNB-X62-Y38 in CDCl3. [Figure 6] FIG. 6 shows the 1H NMR spectrum of the tetrablock PNB-X68-Y32 in CDCl3. [Figure 7]FIG. 7 shows a representative GPC trace of PNB-X67-Y33, showing the sequential growth of each block during the formation of the tetrablock copolymer. [Figure 8] FIG. 8 shows the SAXS spectrum of the tetrablock copolymer poly(BuNB-b-BPNB-b-BuNB-b-BPNB) film in the bromide ion form. [Figure 9] Figure 9 shows TEM micrographs of PNB-X74-Y26 (panel a), PNB-X70-Y30 (panel b), PNB-X67-Y33 (panel c), PNB-X62-Y38 (panel d), and PNB-X54-Y46 (panel e). [Figure 10] FIG. 10 shows the ionic conductivity of polynorbornene AEM at different temperatures. [Figure 11] FIG. 11 shows an Arrhenius plot of lnσ versus inverse temperature for polynorbornene AEM. [Figure 12] FIG. 12 shows the alkaline stability of polynorbornene AEM in 1 M NaOH solution at 80° C. [Figure 13] FIG. 13 shows the TGA trace of polynorbornene AEM under nitrogen atmosphere. [Figure 14] Figure 14 shows polarization data for PNB-X62-Y38 AEMFCs with and without iR compensation (2.1 mg cm-2 Pt, 40% ionomer to carbon ratio). The cell temperature was 60 °C, and the anode and cathode dew points were both set at 46 °C. The humidified H2 and O2 flow rates were both 0.5 L / min. [Figure 15] FIG. 15 shows a GPC trace of PNB-X34-Y66, showing the sequential growth of each block during the formation of the tetrablock copolymer. [Figure 16] FIG. 16 shows the 1H NMR spectrum of the tetrablock PNB-X34-Y66 in CDCl3. [Figure 17] FIG. 17 shows a plot of the ionic conductivity of the XL AEM at different temperatures. [Figure 18] FIG. 18 shows the variation of hydroxide ion conductivity with cross-linker concentration. [Figure 19] Figure 19 shows the alkaline stability of crosslinked AEM in 1 M NaOH solution at 80 °C. Monitoring the decrease in OH- conductivity over time (left). FT-IR spectrum of XL10-PNB-X34-Y66 to characterize the chemical structure (right). [Figure 20] FIG. 20 shows the SAXS spectrum of a cross-linked tetrablock copolymer poly(BuNB-b-BPNB-b-BuNB-b-BPNB) film in the bromide ion form. [Figure 21] Figure 21 shows polarization data for XL5-PNB-X34-Y66 AEMFCs with and without iR compensation (2.1 mg cm-2 Pt, 40% ionomer to carbon ratio). The cell temperature was 60 °C, and the anode and cathode dew points were both set at 52 °C and 56 °C, respectively. The humidified H2 and O2 flow rates were both 0.5 L / min. [Figure 22] FIG. 22 shows the GPC-RI traces (before and after hydrogenation) of rPNB-X60-Y40 for aliquots of the first block and diblock. [Figure 23] FIG. 23 shows the 1H NMR spectra of the diblock copolymer before and after hydrogenation. [Figure 24] FIG. 24 shows the SAXS spectrum of the dried film in the Br-form (numbers are cross-linker concentrations). [Figure 25] FIG. 25 shows TEM micrographs of XL35-rPNB-X60-Y40 (a), XL20-rPNB-X22-Y78 (b), and XL20-rPNB-LY100 (c) membranes in the Br-form. [Figure 26] FIG. 26 shows the water uptake (panel a), swelling ratio (panel b) and λ (panel c) of the membranes at 25° C. as a function of cross-linker concentration. [Figure 27] FIG. 27 shows the hydroxide ion conductivity of the membranes (panel a) and the Arrhenius plot of the XL-rPNB membrane (panel b) as a function of cross-linker concentration. [Figure 28]FIG. 28 shows the hydroxide ion conductivity (20° C.-30° C.) as a function of hydration number (λ) for the AEM of XL-rPNB compared to AEMs reported in the literature. [Figure 29A] Figure 29A shows the endothermic DSC thermograms of XL35-rPNB-X60-Y40, XL20-rPNB-X22-Y78, and XL20-rPNB-LY100 in the Br-form. The graphs have been shifted vertically to avoid overlap. [Figure 29B] Figure 29B shows the TGA curves of XL35-rPNB-X60-Y40, XL20-rPNB-X22-Y78, and XL20-rPNB-LY100 in the Br-form. [Figure 30] FIG. 30 shows the stress-strain curves of fully hydrated and dry XL-rPNB membranes. [Figure 31A] Figure 31A shows the alkaline stability, i.e., OH conductivity as a function of degradation time at 25 °C, of ​​XL20-rPNB-LY100 (A), XL20-rPNB-X22-Y78 (B), and XL35-rPNB-X60-Y40 (C) after immersion in 1 M NaOH at 80 °C. [Figure 31B] Figure 31B shows the alkaline stability, i.e., zoomed-in FT-IR spectra, of XL20-rPNB-LY100 (A), XL20-rPNB-X22-Y78 (B), and XL35-rPNB-X60-Y40 (C) after immersion in 1 M NaOH at 80 °C. [Figure 32] FIG. 32 shows the polarization and power density curves of the XL20-rPNB-LY100, XL20-rPNB-X22-Y78, and XL35-rPNB-X60-Y40 AEMFCs. [Figure 33] FIG. 33 shows the EIS data at 60° C. [Figure 34] Figure 34 shows a comparison of the best peak performance after RH optimization. A / C indicates the dew point in degrees Celsius for the anode (A) and cathode (C), respectively. The cell temperature for all samples was 60°C. [Figure 35] FIG. 35 shows the power density and cell voltage of the XL AEM at 80°C. [Figure 36] FIG. 36 shows the current density versus cell voltage for XL15 at 80°C. [Figure 37] Figure 37 shows the polarization curves of GT64-15 at various anode and cathode inlet RH in BOL. H2 / O2. [Figure 38] Figure 38 shows the polarization curves of GT64-2.5 at various anode and cathode inlet RH in BOL. H2 / O2. [Figure 39] Figure 39 shows the polarization curves of GT64-10 at various anode and cathode inlet RH in BOL. H2 / O2. [Figure 40] Figure 40 shows the performance of the GT64-15 at 75 / 75 / 80. [Figure 41] Figure 41 shows the performance of the GT64-15 over time. [Figure 42] FIG. 42 shows representative DSC cooling and heating curves and enthalpy integrals for AEM (XL5-PNB-X34-Y66) with low crosslinking concentration. [Figure 43] FIG. 43 shows representative DSC cooling and heating curves and enthalpy integrals for a highly crosslinked AEM (XL20-PNB-X34-Y66). DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will now be described more fully below. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0023] The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used in the description of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that words, e.g., words defined in commonly used dictionaries, should be interpreted to have a meaning consistent with their meaning in the context of this application and the related art, and should not be interpreted in an idealized or overly formal sense unless so expressly defined herein. The terms used in describing the invention herein are merely for the purpose of describing particular embodiments and are not intended to limit the invention. All publications, patent applications, patent documents, and other references mentioned herein are incorporated by reference in their entirety. In the event of a conflict in terminology, the present specification controls.

[0025] Also, as used herein, "and / or" refers to and includes any and all possible combinations of one or more of the associated listed items, and refers to and includes excluding combinations when interpreted as alternatives ("or").

[0026] Weight percentages (wt %) of components are based on the total weight of the formulation or composition in which the component is included, unless otherwise specified.

[0027] Mole percentages (mol %) of components are based on the total number of moles of each unit of the formulation or composition in which the component is included, unless otherwise specified.

[0028] As used herein, unless expressly indicated otherwise, "molecular weight" refers to1 It refers to number average molecular weight, as determined by 1 H NMR spectroscopy or other analytical methods such as gel permeation chromatography.

[0029] As used herein, a "copolymer" is a polymer made from the reaction of at least two different monomers and two or more types of units.

[0030] As used herein, a "multiblock polymer" (or segmented block copolymer) is a copolymer consisting of alternating homogeneous segments (i.e., blocks) of at least two different monomers covalently bonded to each other. These monomers, when chemically distinct, are significantly different from their respective random copolymers or homopolymer blends. The segments of a "block" can also vary in size and molecular weight, depending on the number of monomers present in each block. Each block of a multiblock copolymer need not be the same molecular length. For example, the block length of each block in a tetrablock copolymer can have a unique value.

[0031] The term "hydration number," as used herein, refers to the number of water molecules that can combine with an ion in an aqueous solution of a given concentration.

[0032] The term "water uptake (WU) percentage" is the amount of water, expressed as a percentage, that is adsorbed by a polymer, i.e., if the polymer contains water, the weight of water in the polymer divided by the total weight of the polymer.

[0033] The term "swell ratio," as used herein, refers to the amount of liquid material that can be absorbed by the copolymer.

[0034] The term "ion exchange capacity" refers to the charge equivalents per mass of polymer. Ion exchange capacity can be expressed as millicharge equivalents per gram of polymer, meq. / g. Divalent ions in a polymer have twice the charge equivalents compared to monovalent ions.

[0035] The term "hydroxide ion conductivity" refers to the ionic conductance of hydroxide ions within a polymer, as can be measured by conductivity or impedance measurements known to those skilled in the art. The units of ionic conductivity are siemens / cm (S / cm) or 1 / (ohm-cm). A siemen is an inverse ohm.

[0036] The term "monomer," as used herein, refers to one of the building blocks used to synthesize a polymer.

[0037] The term "crosslinker," as used herein, refers to a molecule, ion, or other chemical unit that can form a chemical unit that links two portions of the same polymer chain or two different polymer chains.

[0038] The term "alkyl," as used herein, refers to a branched or unbranched saturated hydrocarbon group of 1 to 20 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, etc. Alkyl groups can also be substituted or unsubstituted.

[0039] The term "quaternary ammonium" as used herein refers to a compound of the formula NA4 + (A can be hydrogen or a hydrocarbon).

[0040] Anion exchange membranes (AEMs) are of interest for several electrochemical devices (i.e., fuel cells, electrolyzers, redox flow batteries) (Mekhilef, S. et al., Renewable Sustainable Energy Rev. 2012, 16, 981-989; Carrette, L. et al., Fuel Cells 2001, 1, 5-39). The development of AEMs with long-term alkaline stability and high hydroxide ion conductivity is currently a topic of interest (Winter, M. et al., Chem. Rev. 2004, 104, 4245-4269; Steele, BC et al., Nature 2001, 414, 345-352; Varcoe, JR et al., Energy Environ. Sci. 2014, 7, 3135-3191; Lu, S.; Pan, J. et al., Proc. Natl. Acad. Sci. USA 2008, 105, 20611-20614). Operation of fuel cells and electrolyzers at high pH allows the use of non-precious metal catalysts, particularly for oxygen reduction and evolution, and reduced fuel crossover compared to proton-exchange membrane (PEM) devices (Yu, EH et al., Energy Environ. Sci. 2012, 5, 5668-5680; Hickner, MA et al., J. Polym. Sci. Part B: Polym. Phys. 2013, 51, 1727-1735; Zhou, J. et al., J. Electrochem. Soc. 2013, 160, F573-F578; Mohanty, AD et al., J. Mater. Chem. A 2014, 2, 17314-17320; Liu, L. et al., J. Mater. Chem. A 2016, 4, 16233-16244).Early AEMs had low ionic conductivity, poor stability at high pH, ​​and high water uptake (Mandal, M. et al., J. Membr. Sci. 2019, 570-571, 394-402; Mohanty, AD et al., J. Electrochem. Soc. 2017, 164, F1279-F1285; Arges, CG et al., ACS Appl. Energy Mater. 2018, 1, 2991-3012). However, recent studies have shown that tethered long-chain trimethylammonium (TMA) cations are stable in alkaline environments at elevated temperatures (Zhang, X. et al., Polym. Chem. 2018, 9, 699-711; Shi, Q. et al., Polymer 2017, 121, 137-148; Weiber, EA et al., Polym. Chem. 2015, 6, 1986-1996; Akiyama, R. et al., Macromolecules 2016, 49, 4480-4489). High hydroxide ion conductivity is crucial in membranes for fuel cells, batteries, and electrolyzers. The use of multiblock copolymers can improve hydroxide ion mobility compared to random copolymers (Shimada, M. et al., J. Polym. Sci. Part A: Polym. Chem. 2016, 54, 935-944). This is due to the higher degree of phase separation in block copolymers compared to random copolymers, which results in the formation of efficient ion channels. Furthermore, water management in membranes can play an important role in controlling mechanical deformation (i.e., water swelling) and ionic conductivity. Water is necessary in membranes to form ionic hydration shells for mobile hydroxide ions and fixed cations. However, excessive water uptake can swell the ion-conducting channels, reducing ionic conductivity (i.e., reducing ion mobility) and potentially softening the membrane. Therefore, it is necessary to optimize the ion-conducting channel size so that the amount of free, unbound (non-productive) water is minimized.

[0041] The long-term stability of AEMs varies greatly depending on the chemistry of the polymer backbone, the location of the cations within the polymer structure, and the chemistry of the anchoring cations. Previously, polymers based on poly(arylene ether sulfone) (Fujimoto, C. et al., J. Membr. Sci. 2012, 423-424, 438-449; Nunez, SA et al., ACS Macro Lett. 2013, 2, 49-52; Arges, CG et al., Proc. Natl. Acad. Sci. USA 2013, 110, 2490-2495) and poly(arylene ether ketone) (Long, H. et al., J. Phys. Chem. C 2012, 116, 9419-9426; Lee, WH et al., ACS Macro Lett. 2015, 4, 453-457) have been investigated as AEMs. Significant decomposition was observed at high pH. The polysulfone and polyketone groups in the polymer backbone were susceptible to nucleophilic attack by hydroxide ions. The poly(aryl ether) backbone underwent C-O bond cleavage at high pH, ​​thereby limiting its long-term use (Ono, H. et al., J. Mater. Chem. A 2017, 5, 24804-24812; Lee, W. H et al., ACS Macro Lett. 2015, 4, 814-818; Park, D. Y. et al., J. Phys. Chem. C 2013, 117, 15468-15477).

[0042] In addition to the polymer backbone, nucleophilic attack of the anchoring cationic head group also leads to degradation. The decomposition mechanism of the quaternary ammonium head group is β-hydrogen Hoffmann elimination, direct nucleophilic substitution (S N2) and elimination via ylide formation (Chen, XC et al., Nano Lett. 2014, 14, 4058-4064; Inceoglu, S. et al., ACS Macro Lett. 2014, 3, 510-514). Hibbs et al. found that a hexamethylene spacer between the trimethylammonium (TMA) cation and the polymer backbone provides better stability than the trimethylbenzylammonium (BTMA) cation in 4 M KOH at 80 °C (Sun, J. et al., J. Am. Chem. Soc. 2014, 136, 14990-14997). Miyatake et al. optimized the length of the pendant chain and found that a side chain with three carbon atoms provided a balance between high conductivity and low water uptake of AME (Ahmad Mahmoud, et al., J. Mater. Chem. 2018, 6, 1440-14409). Later, Mohanty et al. compared the stability of small molecules and reported that a quaternary ammonium head group tethered to the backbone by a long alkyl chain had the best alkaline stability. The cation attached to the long alkyl chain increases the barrier to the Hoffmann elimination reaction, minimizing the risk of decomposition (Sun, J. et al., Macromolecules 2016, 49, 3083-3090). Polymers with a combination of an all-hydrocarbon backbone and quaternary ammonium groups tethered to long alkyl chains were observed to have the best long-term alkaline stability (Price, SC et al., Macromolecules 2013, 46, 7332-7340; Meek, KM et al., Macromolecules 2015, 48, 4850-4862; He, X. et al., RSC Adv. 2015, 5, 63215-63225).

[0043] Price et al. synthesized hydrogenated poly(norbornene) as an anion exchange membrane by ring-opening metathesis polymerization (ROMP), which had a high ionic conductivity of 177 mS / cm at 80 °C. Although the membrane had high conductivity, it was mechanically weak and unstable under alkaline conditions (Kim, D.-G. et al., Chem. Mat. 2015, 27, 6791-6801). described the synthesis of block copolymers by vinyl addition polymerization of substituted norbornenes in living polymerization and their use as pervaporation membranes (He, SQ et al., J. Membr. Sci. 2016, 509, 48-56; Xu, W. et al., Adv. Funct. Mater. 2015, 25, 2583-2589; Wang, J. et al., J. Membr. Sci. 2012, 415-416, 205-212). Previous studies have demonstrated that high T g Polynorbornene at 385°C has been shown to have excellent stability (Tibbits, AC et al., J. Electrochem. Soc. 2015, 162, F1206-F1211).

[0044] In this disclosure, a facile synthetic strategy was used to prepare a series of tetrablock AEM copolymers based on the vinyl addition polymerization of norbornene, as shown in Scheme 1.

[0045] AEMs were cast from solution to evaluate the effects of bound and unbound water on conductivity. Surprisingly, tetrablock AEM copolymers containing light crosslinking exhibited high IEC while maintaining good hydroxide ion mobility. Furthermore, high thermal stability, excellent mechanical properties, and negligible degradation at high pH (1 M NaOH solution at 80 °C) over long periods of time were demonstrated. The AEMs were used as membranes in all-alkaline fuel cells.

[0046] Accordingly, one aspect of the present invention relates to multi-block copolymers comprising one or more hydrophilic blocks based on norbornene and one or more hydrophobic blocks. In some embodiments, one or more hydrophobic blocks are norbornene-based hydrophobic blocks. The norbornene-based hydrophobic block comprises a hydrophobic monomer having a norbornene structure substituted with a branched or unbranched saturated C1-C20 alkyl chain (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, or C20 alkyl chain). In some embodiments, the alkyl chain can be halogenated (i.e., contains one or more halogens (e.g., Cl, Br, F, or I) positioned along the alkyl chain). For example, in some embodiments, the alkyl chain is halogenated with bromine, chlorine, or fluorine. In some embodiments, the halogen is located at the terminal position of the halogenated alkyl chain of the hydrophobic monomer. In some embodiments, the alkyl chain is not halogenated. In some embodiments, the alkyl chain is a C3 to C6 alkyl chain. When one or more norbornene-based hydrophobic monomers are combined, a "norbornene-based hydrophobic block" is formed, where the number (n) of norbornene-based hydrophobic monomers can vary. In some embodiments, the number (n) of norbornene-based hydrophobic monomers is from about 10 to about 1,000, from about 100 to about 1,000, or from about 500 to about 1,000. For example, the norbornene-based hydrophobic block present in the multi-block copolymer of the present invention comprises a structure represented by formula (I):

[0047] [ka] where: R1 is a branched or unbranched saturated C1-C20 alkyl chain or halogenated alkyl chain; n is an integer from 1 to about 1,000.

[0048] In some embodiments, one or more hydrophobic blocks are alkene-based hydrophobic blocks. The alkene-based hydrophobic blocks comprise one or more hydrophobic monomers having a structure represented by formula (II):

[0049] [ka] where: R2 and R3 are independently selected from H and branched or unbranched saturated C1-C20 alkyl or halogenated alkyl chains; x is an integer of about 10 to 1,000.

[0050] Norbornene-based hydrophilic blocks include hydrophilic monomers having a norbornene structure substituted with a branched or unbranched saturated C2-C20 alkyl chain (e.g., C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, or C20 alkyl chain) bearing a cationic head group (e.g., a branched or unbranched C2-C20, C2-C10, or C4-C6 alkyl chain). The cationic head group can be any group that carries a positive charge, such as a quaternary ammonium group, - + The cationic head group can be NR3 (where R is H or an alkyl group (e.g., R is methyl, ethyl, etc.)). The cationic head group can be terminal or non-terminal. In some embodiments, two or more cationic head groups are present in the norbornene-based hydrophilic monomer. In some embodiments, the norbornene-based hydrophilic monomer comprises a norbornene structure substituted with a saturated C4-C10 alkyl chain terminating in a positively charged quaternary ammonium cationic head group. When one or more norbornene-based hydrophilic monomers are combined, a "norbornene-based hydrophilic block" is formed, where the number (m) of norbornene-based hydrophilic monomers can vary. In some embodiments, the number (m) of norbornene-based hydrophilic monomers is from about 10 to about 1,000, from about 100 to about 1,000, or from about 500 to about 1,000.

[0051] For example, the norbornene-based hydrophilic block present in the multi-block copolymer of the present invention comprises a structure represented by formula (III):

[0052] [ka] where: R4 is a branched or unbranched saturated C2-C20 alkyl chain with one or more cationic head groups; m is an integer of about 10 to 1,000.

[0053] In some embodiments, the cationic head group is a quaternary ammonium head group (e.g., - + In some embodiments, the cationic head group is a terminal quaternary ammonium head group (e.g., -N(CH3)3), where R is a branched or unbranched saturated C1-C10 alkyl chain (e.g., -CH3). + In some embodiments, R4 is a saturated C3 (i.e., propyl) or C4 (i.e., butyl) alkyl chain. In some embodiments, R4 is a terminal cationic head group (e.g., -N(CH3)3 + ) is a C3 or C4-alkyl chain (e.g., propyl or butyl).

[0054] In some embodiments, the multiblock copolymer comprises 2, 3, 4, 5, 6, 7, 8, 9, 10, or more blocks, which are hydrophilic and / or hydrophobic (e.g., a norbornene-based hydrophilic block, a norbornene-based hydrophobic block, and / or an alkene-based hydrophobic block). In some embodiments, the multiblock copolymer comprises one or more norbornene-based hydrophilic blocks and one or more norbornene-based hydrophobic blocks. In some embodiments, the multiblock copolymer comprises one or more norbornene-based hydrophilic blocks and one or more alkene-based hydrophobic blocks. In some embodiments, the multiblock copolymer comprises 2 to 8 blocks. In some embodiments, the hydrophilic and / or hydrophobic blocks alternate in the multiblock copolymer. In some embodiments, the multiblock copolymer comprises an all-hydrocarbon backbone.

[0055] In some embodiments, the amount of hydrophobic block present in the multi-block copolymers of the present invention can vary. For example, in some embodiments, the multi-block copolymers of the present invention comprise from about 30% to about 40% (or from about 30% to about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, or about 40%) mole percent of one or more hydrophobic blocks. For example, in some embodiments, the multi-block copolymers of the present invention comprise from about 10% to about 30% (or from about 10% to about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, or about 30%) weight percent of one or more hydrophobic blocks.

[0056] In some embodiments, the amount of hydrophilic block present in the multi-block copolymers of the present invention can vary. For example, in some embodiments, the multi-block copolymers of the present invention comprise from about 60% to about 70% (or about 60%, about 61%, about 62%, about 63%, about 64%, 65%, 66%, 67%, 68%, 69%, or 70%) mole percent of one or more hydrophilic blocks. For example, in some embodiments, the multi-block copolymers of the present invention comprise from about 70% to about 90% (or about 70%, to about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, or about 90%) weight percent of one or more hydrophobic blocks.

[0057] In some embodiments, the multi-block copolymers of the present invention have a ratio of norbornene-based hydrophilic monomers to hydrophobic monomers of about 1:250 to about 250: 1. For example, the ratio of norbornene-based hydrophilic monomers to hydrophobic monomers is about 1:250, 1:200, 1:100, 1:75, 1:50, 1:25, 1:20, 1:15, 1:10, 1:5, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 50:1, 75:1, 100:1, 200:1, or 250:1.

[0058] In some embodiments, each norbornene-based hydrophilic block and / or hydrophobic block present in the multi-block copolymer comprises a molecular weight of about 5 to about 20 kDa or about 5 to about 15 kDa.

[0059] In some embodiments, the multi-block copolymer comprises a molecular weight of about 10 to about 75 kDa or about 20 to about 45 kDa.

[0060] In some embodiments, the multi-block copolymers of the present invention are cross-linked with a cross-linking agent. Cross-linking is the process of chemically bonding one polymer chain to another, or alternatively, chemically bonding a portion of a chemical chain to another portion of the same chain. Cross-linking a polymer can adjust mechanical properties by creating new bonds that change how the polymer behaves under mechanical stress. Variables such as cross-link density and the chemical nature of the cross-links can further alter the final properties of the polymer. The disclosed multi-block copolymers are cross-linked with a cross-linking agent containing at least two functional groups that can react with chemical sites on the multi-block copolymer. The end result is the creation of chemical cross-links that incorporate the cross-linking agent.

[0061] In some examples, the crosslinker can include two or more reactive groups (e.g., three or more, four or more, or five or more). In some examples, the crosslinker can include six or fewer reactive groups (e.g., five or fewer, four or fewer, or three or fewer). The number of reactive groups on the crosslinker can range from any of the minimum values ​​described above to any of the maximum values ​​described above, for example, from 2 to 6 (e.g., 2 to 4, 4 to 6, 3 to 5, 2 to 3, 3 to 4, 4 to 5, or 5 to 6). Suitable reactive groups on the crosslinker include, but are not limited to, nucleophilic groups, such as amines. In some embodiments, the crosslinker is a multiamine comprising a branched or unbranched saturated C2-C10 alkyl chain having at least two amine functional groups (i.e., reactive groups). In some embodiments, the crosslinker is an alkyldiamine comprising a branched or unbranched C2-C10 alkyl chain. Exemplary crosslinkers include, but are not limited to, ethylenediamine, propyldiamine, butyldiamine, 1,5-pentanediamine, and / or 1,6-hexanediamine. In some embodiments, the crosslinker is a C alkyldiamine (e.g., 1,6-hexanediamine).

[0062] Functional groups suitable for crosslinking that are incorporated into the copolymer include electrophilic functional groups, such as, but not limited to, electrophilic carbon atoms, such as carbon atoms bonded to leaving groups, e.g., halogens (e.g., Cl, Br, F, I) or sulfonates (e.g., mesylate, triflate, tosylate). Thus, crosslinking of copolymers of the present invention containing electrophilic functional groups, e.g., carbons bonded to leaving groups, with crosslinkers containing nucleophilic functional groups (e.g., -NR groups (R is H or alkyl)) can be achieved by a nucleophilic substitution reaction (S N 2) reaction.

[0063] The amount of crosslinking, and therefore the number of reactive groups on the copolymer participating in the reaction, can be controlled by selecting the desired amount of crosslinking agent. That is, stoichiometric amounts of reagents can be used to determine the degree of crosslinking. The amount of crosslinking can be monitored by various analytical techniques, such as thin layer chromatography, infrared spectroscopy, gel permeation chromatography, and NMR. The mole percent of crosslinking agent used in the crosslinking reaction can be about 1% or more relative to the total moles of sites on the polymer available for crosslinking. As used herein, percentages refer to mole percent, and are sometimes expressed as mole % (e.g., about 1% or more, about 3% or more, about 5% or more, about 10% or more, about 15% or more, about 20% or more, about 25% or more, about 30% or more, about 35% or more, about 40% or more, or about 45% or more). In some examples, the amount of crosslinker used can be about 10% or less (e.g., about 9% or less, about 8% or less, about 7% or less, about 6% or less, about 5% or less, about 4% or less, about 3% or less, about 2% or less, or about 1% or less) of the total number of sites in the polymer available for crosslinking. The amount of crosslinker used can range from any of the minimum values ​​described above to any of the maximum values ​​described above. For example, the amount of crosslinker used can be about 1% to about 50% (e.g., about 1% to about 50%, about 5% to about 50%, about 10% to about 40%, or about 20% to about 30%) of the total amount of monomers polymerized.

[0064] Accordingly, some embodiments of the present invention relate to a method for preparing a crosslinked multi-block copolymer, comprising crosslinking one or more hydrophilic blocks of the multi-block copolymer with one or more crosslinking agents as described above. In some embodiments, the crosslinking agent is a multi-amine alkyl chain comprising a branched or unbranched saturated C2-C10 alkyl chain having at least two amine functional groups. One or more hydrophilic blocks of the multi-block copolymer comprises a saturated C1-C20 halogenated alkyl chain. Those skilled in the art will recognize that the saturated C1-C20 halogenated alkyl chain contains at least one electrophilic carbon atom (i.e., a carbon atom bonded to a leaving group, e.g., a halogen) as described above.

[0065] In some embodiments, the crosslinked copolymer comprises one or more cationic head groups (e.g., -) of one or more norbornene-based hydrophilic monomers. + The crosslinker comprises one or more branched or unbranched saturated C2-C20 alkyl chains bonded to NR3 (where R is H or alkyl). For example, in some embodiments, the crosslinked copolymer comprises a crosslinker having a C4-C6 alkyl chain. In some embodiments, the cationic head groups of one or more norbornene-based hydrophilic monomers are crosslinked to each other via the alkyl chain crosslinker.

[0066] For example, in some embodiments, the copolymer of the present invention comprises a structure represented by formula (IV):

[0067] [ka] where: R4 is a branched or unbranched saturated C1-C20 alkyl chain; R1 is a branched or unbranched saturated C2-C20 alkyl chain; X is a cationic head group containing a cationic charged heteroatom (e.g., + N(R)2), where R is a branched or unbranched C1-C10 alkyl chain (e.g., —CH3); R5 is a crosslinker containing a branched or unbranched saturated C2-C10 alkyl chain; n, m, o, and p are integers independently selected from about 1 to about 1,000.

[0068] The concentration of crosslinker present in the copolymer can vary. For example, in some embodiments, the crosslinker concentration is about 5 to about 50%, about 10 to about 40%, about 20 to about 30% (or at least about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, or at least about 50%). All of these are expressed as mole percents.

[0069] Another aspect of the present invention is directed to an anion exchange membrane comprising the multiblock copolymer composition of the present invention. In some embodiments, the AEM of the present invention comprises one or more crosslinked multiblock copolymers as described above. In some embodiments, the AEM of the present invention comprises one or more non-crosslinked multiblock copolymers as described above. In some embodiments, the AEM of the present invention comprises hydrophobic and hydrophilic regions within the multiblock copolymer and / or within the AEM that form due to phase separation within the block copolymer. The presence of one or more anion-conducting channels in the copolymer promotes the conductive properties of the AEM.

[0070] In some embodiments, the AEM of the present invention has an ion exchange capacity of about 1.5 to about 4.5 meq. / g, about 1.75 meq. / g to about 4.25 meq. / g, about 2.0 meq. / g to about 4.00 meq. / g, about 2.25 meq. / g to about 3.75 meq. / g, about 2.50 meq. / g to about 3.75 meq. / g, about 2.75 meq. / g to about 3.75 meq. / g, about 3.00 meq. / g to about 3.50 meq. / g, or about 3.25 meq. / g to about 3.50 meq. / g (or at least about 1.5 meq. / g, about 2 meq. / g, about 2.5 meq. / g, about 3 meq. / g, about 3.5 meq. / g, or at least about 4 meq. / g).

[0071] In some embodiments, the AEM of the present invention comprises a hydroxide ion conductivity of about 25 to about 275 mS / cm, about 35 to about 250 mS / cm, about 50 to about 225 mS / cm, about 75 to about 200 mS / cm, about 100 to about 175 mS / cm, or about 125 to about 175 mS / cm (or at least about 25 mS / cm, about 50 mS / cm, about 75 mS / cm, about 100 mS / cm, about 125 mS / cm, about 150 mS / cm, about 175 mS / cm, about 200 mS / cm, about 225 mS / cm, or at least about 250 mS / cm). Hydroxide ion conductivity can be measured at various temperatures. For example, in some embodiments, hydroxide ion conductivity is measured at a temperature of about 20°C to about 100°C, about 25°C to about 80°C, or about 25°C to about 65°C (or at least about 25°C, about 35°C, about 45°C, about 55°C, about 65°C, about 75°C, about 85°C, or at least about 95°C).

[0072] In some embodiments, the AEM of the present invention has a water uptake percentage of about 10% to about 80%, about 15% to about 75%, about 25% to about 65%, or about 40% to about 60% (or at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, or at least 90%).

[0073] In some embodiments, the AEM of the present invention has a hydration number of about 5 to about 30, about 5 to about 25, about 5 to about 20, or about 5 to about 15 (or at least about 5, about 10, about 15, about 20, or at least about 25).

[0074] In some embodiments, the AEM of the present invention has an expansion ratio of about 15% to about 50%, about 20% to about 40% (or at least about 10%, about 20%, about 30%, or about 40%).

[0075] In some embodiments, the AEM of the present invention comprises about 1 to about 10 or about 3 to about 6 (or at least about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, or at least about 9) freezable water molecules per ion pair.

[0076] In some embodiments, the AEMs of the present invention comprise from about 1 to about 50 or from about 10 to about 25 (or at least about 5, about 10, about 15, about 20, about 25, about 30, about 35, about 40, or at least about 45) bound water molecules per ion pair.

[0077] In some embodiments, the AEM of the present invention is stabilized and / or reinforced with a stabilizer. The stabilizer can be any agent known in the art for adjusting the physical properties of a copolymer to increase its stability and durability against external stressors. Examples of stabilizers include, but are not limited to, perfluorinated tetrafluoroethylene (PFTE) or polyolefins (PO). The stabilizer can be in the form of a woven or nonwoven fabric or individual fibers. The size of the individual strands of the stabilizer can range from molecular-sized strands to macrostrands, with dimensions of 0.01 to 1.0 mm or larger. The physical properties of the AEM, such as tensile strength, elongation at break, and Young's modulus, can be adjusted using a stabilizer.

[0078] The amount of stabilizer present in the AEM varies and depends on the type of stabilizer used and the desired physical properties to be obtained. For example, in some embodiments, the amount of stabilizer is about 2% to 80% by weight. In some cases, the amount of stabilizer is 10% to 50% by weight. A higher amount of stabilizer may result in a stronger composite film, but at the expense of ionic conductivity, as the stabilizer may contribute less or nothing to ionic conductivity.

[0079] In some embodiments, the AEMs of the present invention exhibit a tensile strength of about 10 to about 500 MPa, about 10 to about 250 MPa, about 12 to about 175 MPa, about 12 to about 150 MPa, or about 14 to about 45 MPa (or at least about 10 MPa, about 25 MPa, about 50 MPa, about 75 MPa, about 100 MPa, about 125 MPa, about 150 MPa, about 175 MPa, about 200 MPa, about 250 MPa, about 300 MPa, about 325 MPa, about 350 MPa, about 375 MPa, about 400 MPa, about 425 MPa, about 450 MPa, or at least about 475 MPa). The term "tensile strength" describes the resistance of a material (i.e., the AEMs of the present invention) to fracture under tension.

[0080] In some embodiments, the AEM of the present invention exhibits an elongation to break of about 10% to about 200%, about 25% to about 175%, or about 45% to about 155% (or at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 100%, about 110%, about 120%, about 130%, about 140%, about 150%, about 160%, or at least 170%). The term "elongation to break" describes the elongation present at the moment of rupture of a standardized test specimen (i.e., an AEM of the present invention). The elongation at break is expressed as a percentage of the initial length before stretching.

[0081] In some embodiments, the AEM of the present invention has a tensile strength of about 0.0010 to about 1 GPa, 0.0050 to about 1 GPa, about 0.0050 to about 0.0200 GPa, about 0.0050 GPa to about 0.0175 GPa, or about 0.0075 GPa to about 0.0150 GPa (or at least about 0.0010 GPa, about 0.0050 GPa, about 0.0100 GPa, about 0.1 GPa, about 0.2 GPa, about 0.3 GPa, or ...75 GPa to about 0.0150 GPa). The AEM may exhibit a Young's modulus (i.e., elastic modulus) of about 0.4 GPa, about 0.5 GPa, about 0.6 GPa, about 0.7 GPa, about 0.8 GPa, or at least about 0.9 GPa. The term "Young's modulus," also known as the modulus of elasticity, describes the mechanical properties of a linear elastic solid material (e.g., an AEM of the present invention) and thus defines the relationship between stress (force applied per unit area) and strain (proportional deformation) in the material.

[0082] Another aspect of the present invention relates to methods for preparing the AEMs and / or multiblock copolymers of the present invention according to methods known in the art. Exemplary methods include, but are not limited to, polymerization of norbornene via vinyl addition polymerization or ring-opening metathesis polymerization (ROMP) to obtain the copolymers of the present invention. For example, polymerization of substituted norbornene molecules in the presence of a metal catalyst (e.g., a Pd-based catalyst) and a solvent results in hydrophobic and / or hydrophilic polymer blocks of polymerized norbornene and / or alkene-based molecules, the polymer having an all-hydrocarbon backbone. The overall ratio of monomer to catalyst used can range from about 1500:1 to about 1:1. For example, the ratio of norbornene monomer to catalyst can be about 1200:1, about 1100:1, about 1000:1, about 750:1, about 500:1, about 100:1, about 50:1, about 10:1, or about 1:1. The sequential and alternating addition of hydrophilic and / or hydrophobic monomers to the growing polymer results in the multi-block copolymer of the present invention. In some embodiments, the solvent comprises a non-polar solvent, such as toluene. The reaction mixture can be allowed to stand at ambient or elevated temperature.

[0083] Another aspect of the present invention relates to a method for preparing a crosslinked multi-block copolymer, comprising crosslinking one or more hydrophilic blocks of the multi-block copolymer with one or more crosslinking agents. In some embodiments, the crosslinking agent is a multiamine alkyl chain comprising a branched or unbranched saturated C2-C10 alkyl chain having at least two amine functional groups. For example, in some embodiments, the crosslinking agent is an alkyl diamine comprising a branched or unbranched saturated C2-C10 alkyl chain. In some embodiments, one or more hydrophilic blocks of the multi-block copolymer comprises a saturated C1-C20 halogenated alkyl chain.

[0084] Another aspect of the present invention relates to a device comprising the copolymer of the present invention and / or the AEM of the present invention. In some embodiments, the device is an electrochemical device. In some embodiments, the electrochemical device is selected from a fuel cell, an electrolyzer, and a redox flow battery. In some embodiments, the electrochemical device is a fuel cell. In some embodiments, the fuel cell is part of a stationary power generator and / or a portable electronic device.

[0085] Example The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices, and / or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their invention. However, those of ordinary skill in the art should recognize in light of the present disclosure that many changes can be made in the specific embodiments which are disclosed and still obtain like or similar results without departing from the spirit and scope of the invention.

[0086] Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.

[0087] Example 1 Anionic multiblock copolymer membranes based on vinyl addition polymerization of norbornene: Application in anion exchange membrane fuel cells Materials: 1-hexene, 5-bromo-1-pentene, and dicyclopentadiene were purchased from Alfa Aesar and used as received. The monomers butylnorbornene (BuNB) and bromopropylnorbornene (BPNB) were synthesized by Diels-Alder reaction at elevated temperatures according to published procedures (Martinez-Arranz, S. et al., Macromolecules 43 (2010) 7482-7487). Prior to polymerization, the monomers were purified by distillation over sodium and degassed by three freeze-degassing cycles. All polymerization reactions were carried out in a glove box under a dry argon atmosphere, taking strict precautions to prevent moisture and air from entering. Toluene was dried by heating at reflux over sodium and benzophenone for 6 hours. Toluene was freshly distilled before use. Triisopropylphosphine and [(η 3 The catalyst (allyl)palladium(triisopropylphosphine) chloride ((η 3 -allyl)Pd( i PrP)Cl) was prepared according to a previously published report (Lipian, J. et al., Macromolecules 35 (2002) 8969-8977). Lithium tetrakis(pentafluorophenyl)-borate·(2.5EtO) (Li[FABA]) was purchased from Boulder Scientific Co. and used as received. α,α,α-Trifluorotoluene (TFT), anhydrous, ≥99%, and tetrahydrofuran (THF) were purchased from Sigma-Aldrich and used as received.

[0088] Synthesis of tetrablock copolymer [poly(BuNB-b-BPNB-b-BuNB-b-BPNB)]: A tetrablock copolymer consisting of alternating butylnorbornene (BuNB) and bromopropylnorbornene (BPNB) blocks (two blocks each) was synthesized by sequential addition of the monomers (one added, then the other) at room temperature in an inert atmosphere glove box. The monomers were divided into four round-bottom flasks (two for each monomer), and toluene was added to each flask to produce a 5 wt. % solution. The catalyst solution was (η 3 -allyl)Pd( iA separate vial was prepared by dissolving PrP)Cl (12 mg, 0.03 mmol) and Li[FABA] (28 mg, 0.03 mmol) in a solution composed of 0.5 g of toluene and 0.5 g of TFT. The catalyst solution was stirred for 20 min. BuNB (0.45 g, 3.00 mmol) and toluene (10 mL) were added to a 100 mL round-bottom flask equipped with a magnetic stir bar. The catalyst solution was poured into the flask with vigorous stirring. After 20 min, the BuNB polymerization was complete. A small aliquot was removed and quenched with CHCN for gel permeation chromatography (GPC) analysis. Next, a mixture of BPNB (0.64 g, 3.00 mmol) and toluene (12 mL) was added to the reaction flask still containing the catalyst and stirred for 3 h to incorporate the BPNB block onto the BuNB polymer. After 3 hours of reaction time (BPNB was completely consumed), a small aliquot was removed and quenched with CH3CN for GPC analysis. Next, BuNB (0.45 g, 3.00 mmol) and toluene (10 mL) were added to the reaction flask and allowed to react for 20 minutes to incorporate the third block. A small aliquot was again removed and quenched with CH3CN for GPC analysis. Finally, a mixture of BPNB (0.64 g, 3.00 mmol) and toluene (12 mL) was added to the flask and stirred for 3 hours to incorporate the fourth block onto the polymer. After completion, the reaction mixture was quenched, and the polymer was precipitated by adding methanol. The resulting polymer was dissolved in THF and stirred over activated carbon. The solution was passed through an alumina filter to remove any palladium residue. The resulting product was precipitated from THF by adding methanol. The polymer products were dried under vacuum at 60° C. By varying the feed ratio of monomer to catalyst, tetrablock copolymers with different lengths of hydrophobic and hydrophilic chains were synthesized.

[0089] Nuclear magnetic resonance (NMR) spectra and GPC: Polymer samples were 1The polymer samples were analyzed by H NMR using a Bruker Avance 400 MHz NMR instrument with CDCl as the solvent. n ) and polydispersity index (M w / M n ) was determined by GPC (Shimadzu) equipped with an LC-20AD HPLC pump and a refractive index detector (RID-20A, 120V). Measurements were performed at 30 °C using an eluent in THF at a flow rate of 1.0 mL / min. Polystyrene standards were used.

[0090] Membrane casting and ion exchange: The tetrablock copolymer (0.20 g) was dissolved in 5 mL of chloroform, and the resulting solution was filtered through a 0.2 μm poly(tetrafluoroethylene) (PTFE) membrane syringe filter into a 4 cm diameter aluminum dish. The solvent was evaporated at room temperature in a nitrogen gas stream. The membrane was dried overnight under vacuum. The membrane was colorless, flexible, and freestanding with a thickness of approximately 50 μm. The bromobutyl head groups were then quaternized by immersing the membrane in a 45 wt % aqueous trimethylamine solution at room temperature for 48 hours. The quaternized membrane with bromide counterions was removed from the solution and thoroughly washed with DI water. The membrane was then immersed in a 1 M NaOH solution under nitrogen for 24 hours to convert the bromide ions to hydroxide ions. The membrane was washed three times with DI water and then stored in DI water.

[0091] Morphological characterization: Small-angle X-ray scattering (SAXS) was used to analyze the morphology of AEM. Hydrated films in the bromide ion form were tested in air using either a Malvern Panalytical Empyrean XRD (Netherlands) instrument equipped with a Pixel 3D detector or the NSLS-II beamline at the Center for Functional Nanomaterials (Brookhaven National Laboratory, Upton, NY). The wave vector (q) was calculated using Equation 1 below, where 2θ is the scattering angle.

[0092]

number

[0093] The characteristic separation length or interdomain distance (d) (i.e., Bragg spacing) was calculated using Equation 2 below.

[0094]

number

[0095] Transmission electron microscopy (TEM) was also used to analyze the morphology of the films. TEM was performed using a JEOL JEM-1400 transmission electron microscope. Dried films with bromide counterions were stained by smothering with osmium tetroxide at room temperature prior to TEM examination. The stained films were embedded in epoxy resin and sectioned into approximately 50 nm thick samples using a Leica UC6rt Ultramicrotome and placed on copper grids for observation.

[0096] Hydroxide ion conductivity and alkaline stability: The ionic resistance of the membranes was measured using a four-point in-plane probe and electrochemical impedance spectroscopy (1 Hz to 1 MHz) with a PAR2273 potentiostat. All samples were tested in HPLC-grade water under a nitrogen purge to minimize the deleterious effects of CO2. Samples were equilibrated for 30 minutes before each measurement. The in-plane ionic conductivity was calculated using Equation 3 below.

[0097]

number

[0098] In Equation 3, σ is the ionic conductivity (S / cm), L is the length between the sensing electrodes (cm), W and T are the width and thickness of the membrane (cm), respectively, and R is the resistance measured in ohms. Long-term (up to 1200 hours) alkaline stability tests were performed by storing the membrane in a 1 M NaOH solution at 80°C in a Teflon-lined Parr reactor. The ionic conductivity was measured periodically by removing the membrane from the solution, and the membrane was thoroughly washed with DI water before measuring the conductivity. After each measurement, the membrane was placed back into the reactor containing freshly prepared NaOH solution.

[0099] Ion exchange capacity (IEC), water uptake (WU), hydration number (λ), number of freezable water molecules (N free ) and the number of bound unfreezable water molecules (N bound ): The ion exchange capacity was calculated using NMR data, which will be discussed in detail in the next section. Furthermore, the membrane IEC was also measured by titration (Wang, C. et al., J. Membr. Sci. 556 (2018) 118-125). Br - The membrane in the chloride ion form was first immersed in a 0.1 M NaCl solution for 24 hours to exchange bromide ions for chloride ions. The membrane in the chloride ion form was then thoroughly washed with DI water and dried under vacuum for 24 hours to obtain a dry weight. The dried membrane was then immersed in a fixed volume of 0.5 M NaNO3 aqueous solution for 24 hours. The Cl released from the membrane was - The ions were titrated with 0.05 M AgNO3 using K2CrO4 (10 wt%) as indicator. The IEC was calculated using Equation 4 below.

[0100]

number

[0101] In Equation 4, V AgNO3 (mL) is the volume of the AgNO3 solution, and C AgNO3 (0.05 mol L -1) is the concentration of the AgNO3 solution, M d (g) is the weight of the dry membrane sample.

[0102] The water uptake of the membrane was calculated using Equation 5 below.

[0103]

number

[0104] In Equation 5, M d is the dry mass of the membrane, M w is the wet mass of the membrane after removing excess water from the surface. - The hydration number (λ), the number of water molecules per ionic group, was calculated using Equation 6 below.

[0105]

number

[0106] Number of freezable water molecules (N free ) and the number of bound water (or unfreezable water) (N boundThe solubility of the membranes was determined by differential scanning calorimetry (DSC). DSC measurements were performed on a Discovery DSC using an autosampler (TA Instruments). The membrane samples were fully hydrated by immersing them in deionized water once a week. After the water on the membrane surface was wiped off, 5–10 mg of the sample was placed in an aluminum pan and quickly sealed. The sample was cooled to −50°C and then heated to 30°C at a rate of 5°C / min under N2 (20 mL / min). The amounts of freezable and non-freezable water were determined by the following equations 7 to 9 (Lue, SJ et al., J. Macromol. Sci. Part B: Phys. 48 (2009) 114-127; Mecheri, B. et al., J. Phys. Chem. C 116 (2012) 20820-20829; Moster, AL et al., J. Appl. Polym. Sci. 113 (2009) 243-250).

[0107]

number

[0108] M free is the mass of freezable water, and M tot is the total mass of water absorbed in the membrane. The weight fraction of freezable water was calculated using Equation 8 below.

[0109]

number

[0110] H f is the enthalpy obtained by integration of the DSC freezing peak, and H ice is the enthalpy of fusion of water corrected for freezing points below zero according to Equation 9 below:

[0111]

number

[0112] ΔC p is the difference between the specific heat capacity of liquid water and that of ice. ΔT f is the freezing point depression.

[0113] The thermal stability of the dried films in the bromide ion form was studied using thermogravimetric analysis (TGA) on a TA Instruments Q50 analyzer. The temperature was ramped to 800°C at 10°C / min in a nitrogen atmosphere.

[0114] Fabrication of membrane electrode assembly (MEA) and cell testing: One of the best performing membranes in this study (PNB-X 62 -Y 38) was selected for testing in an alkaline exchange membrane fuel cell (AEMFC). The AEM anode and cathode were identical and fabricated by a slurry method. First, a lower molecular weight (20.5 kg / mol) anion exchange ionomer powder of poly(BuNB-b-BPNB-b-BuNB-b-BPNB) tetrablock copolymer was synthesized using the same method as the membranes discussed in this disclosure. Low molecular weight ionomer materials have previously been found to be advantageous for use as polymer binders in the fabrication of fuel cell and electrolyzer electrodes (Ahlfield, J. et al., J. Electrochem. Soc. 164 (2017) F1648-F1653). The dried ionomer powder and Vulcan XC-72 (carbon)-supported 50% platinum catalyst were ground together in 1.5 mL of isopropyl alcohol (IPA) for 10 minutes using a mortar and pestle to generate finer particles. To achieve a slurry viscosity suitable for spraying, an additional 2 mL of IPA was added, and the mixture was milled for an additional 5 minutes. To ensure uniform dispersion, the catalyst and ionomer slurry was further sonicated in a water bath at room temperature for 30 minutes. The homogenized catalyst and ionomer slurry was sprayed onto 1% waterproof Toray TGPH-060 carbon paper and allowed to dry at room temperature for 24 hours. The platinum loading was approximately 2.1 mg / cm. 2 A 40% ionomer / carbon ratio was used. The high metal loading was intentionally chosen to minimize any kinetic losses caused by a non-optimized catalyst.

[0115] Prior to testing the MEA, the electrodes and membrane were soaked in 1 M NaOH in a nitrogen atmosphere for 1 hour (the solution was replaced every 20 minutes) to convert the membrane and ionomer to the hydroxide ion form. The MEA was placed between single-pass serpentine graphite plates with 6-mil PTFE gaskets from Fuel Cell Technologies Hardware. The MEA was tested in a Scribner 850e fuel cell test station at a cell temperature of 60°C. Humidified H2 and O2 feed gases were delivered to the anode and cathode at 0.5 L / min, respectively. The dew points of the anode and cathode streams were adjusted throughout the test to optimize the moisture balance within the AEMFC.

[0116] Synthesis and characterization of tetrablock copolymers: Monomers (BuNB and BPNB) were synthesized by a previously described procedure (Martinez-Arranz, S. et al., Macromolecules 43 (2010) 7482-7487). The catalyst (η 3 -allyl)Pd( i Pr(P)Cl was prepared in high yield and purity according to previous reports (Lipian, J. et al., Macromolecules 35 (2002) 8969-8977). The reactivity of the BuNB monomer ([M] / [Pd] = 100:1) was higher than that of the BPNB monomer. The reaction time for each block was varied (20 min for BuNB and 3 h for BPNB) to achieve complete conversion for each block. A 1:1 molar ratio of Li[FABA] to catalyst was sufficient to generate the cationic Pd complex to initiate the polymerization. The polymer produced 1 The absence of olefinic protons in the H NMR spectrum indicates that the polymerization reaction proceeds via a vinyl addition pathway, precluding the occurrence of ring-opening metathesis polymerization (ROMP), as shown in Figure 1A. 1The H NMR spectra are shown in Figures 2-6. To avoid branching side reactions, the polymerization time of each monomer was optimized for various monomer-to-initiator feed ratios ([M] / [Pd]) (Kim, DG et al., Chem. Mater. 27 (2015) 6791-6801). Incomplete conversion of polymer to monomer would also pose a problem for the synthesis of block copolymers by sequential addition of various monomers (Kim, DG et al., ACS Macro Lett. 4 (2015) 327-330).

[0117] [ka]

[0118] A series of tetrablock copolymers (PNB-X a -Y b PNB-X (where a is the mole percent of combined hydrophobic block X and b is the mole percent of combined hydrophilic block Y) was synthesized by varying the length of the hydrophobic block (BuNB) and the hydrophilic block (BPNB). The block size was changed by adjusting the feed ratio of monomer to initiator ([M] / [Pd]) in toluene during polymerization, as shown in Scheme 1. 67 -Y 33 A representative GPC trace of is shown in Figure 7, which demonstrates the sequential growth of each block in the formation of the tetrablock copolymer. The number average molecular weight (M n ) was determined by GPC analysis. n was found to be 12.32 kDa as shown in Figure 7. Then, the second monomer was added to the reaction mixture and allowed to react for 3 hours. n is 19.80 kDa, and the M of the second block n Similarly, the M of the third and fourth blocks was 7.48 kDa. nThe M of the synthesized polymers was found to be 9.25 kDa and 9.81 kDa, respectively. The properties of the various membranes are shown in Table 1. n The IEC values ​​ranged from 38 to 114.9 kDa with polydispersities of 1.28 to 1.55. 1 The X and Y values ​​in poly(BuNB-b-BPNB-b-BuNB-b-BPNB) were determined by H NMR spectroscopy and found to be 1.55-2.60 meq / g, as discussed later. The methyl protons of the hydrophilic block resonate at 0.89 ppm. The methylene protons adjacent to the bromine atoms of the hydrophilic block appear at 3.41 ppm. The X and Y values ​​in poly(BuNB-b-BPNB-b-BuNB-b-BPNB) were determined by H NMR as shown in Figure 1A. a and H b The mole % and weight % of combined hydrophilic and hydrophobic blocks in the tetrablock copolymers were calculated by NMR spectroscopy.

[0119] [Table 1] a Measured in the bromopropyl form by gel permeation chromatography in THF at room temperature against polystyrene standards. b IEC (ion exchange capacity) is in bromopropyl form, 1 Calculated from H NMR results. c OH - The conductivity was measured by a four-terminal conductivity cell. d Ionic conductivity / IEC at 80°C. e Water uptake was measured at room temperature. f Interdomain distances were measured using small-angle X-ray scattering (SAXS) in the bromide ion form. ND = not determined. PNB = polynorbornene, X = hydrophobic block, Y = hydrophilic block. The subscripts indicate the molar ratio of each block.

[0120] Morphological Characterization: SAXS and / or TEM were used to study the microstructure of the polynorbornene films synthesized here. The interdomain distance (d), or the average separation length between inhomogeneities in the film, was determined from the Bragg spacing of the first scattering peak in the SAXS spectrum, as shown in Figure 8. The interdomain distance values ​​are listed in Table 1. The domain size ranged from 37.2 to 86.4 nm, which correlated directly with water uptake. More specifically, the number of unbound water molecules was found to track with domain size. Larger domains provide areas where free (unbound) water can reside. For example, PNB-X 54 -Y 46 showed very high water uptake of 133.6% and a d-spacing of 86.4 nm. In comparison, these values ​​were higher for PNB-X, which had a water uptake of 68.8% and a d-spacing of 44.2 nm. 67 -Y 33 is about twice the value of

[0121] PNB-X 74 -Y 26was studied using transmission electron microscopy (TEM) because X-ray scattering is not as reliable as for other samples. TEM analysis was performed in the bromide ion form rather than the hydroxide ion form to avoid accidental decomposition of the membrane due to the concentration of hydroxide ions in the dry membrane. The phase size was observed to increase with membrane hydrophilicity. This is consistent with the increasing interdomain distance observed by SAXS. It also appears that ion channels lose their distinct and well-defined structure as channel size increases. Figure 9 shows five TEM micrographs of the membrane. Dark regions correspond to hydrophilic domains with bromide counterions, and light regions correspond to hydrophobic domains. Also, membranes with higher hydrophilicity contain darker regions in the TEM micrographs. Note that the trends observed using dry TEM would likely be more pronounced if the membranes were observed to be swollen with water, as seen in SAXS measurements. Table 2 shows a comparison of the properties of a free-standing AEM film and a film reinforced with perfluorinated tetrafluoroethylene (PTFE) or polyolefin (PO). Figure 1B shows an image of the two films on a background with text. The films are transparent and colorless.

[0122] [Table 2]

[0123] Ion exchange capacity (IEC), hydroxide ion conductivity: IEC is an important parameter that determines the ionic conductivity and water uptake of the membrane. 1 The PNB-X was estimated by H NMR spectroscopy and found to be 1.55-2.60 meq / g. 54 -Y 46 Using a representative sample, the IEC was calculated by comparing the integral ratio of the methylene protons adjacent to the bromine atoms in the hydrophilic block at 3.41 ppm with the methyl protons in the hydrophobic block at 0.89 ppm. a and H bThe integral ratio of PNB-X to PNB-X was 3.46:2, which is equivalent to 1.153:1 (per proton). To further confirm the extent of the quaternization reaction, the IEC was measured by titration. The titration procedure involved converting the counter anion in the membrane to chloride ion, and then titrating the amount of chloride ion present in the membrane, as described in the Experimental Section. Excellent correlation was found between the two methods, titration and NMR, for the IEC. 67 -Y 33 In this case, the IEC measured by titration and NMR was found to be 1.90 meq / g and 1.92 meq / g, respectively.

[0124] High hydroxide ion conductivity (σ) is desirable in membranes used in electrochemical devices (Wang, YJ et al., Chem. Soc. Rev. 42 (2013) 5768-5787). Figure 10 shows that the hydroxide ion conductivity increased with temperature from 25°C to 80°C and followed the Arrhenius relationship. 68 -Y 32 The conductivity of the membrane (PNB-X) was 122.7 mS / cm at 80°C. 54 -Y 46 ) is PNB-X 68 -Y 32 The membranes had the highest IEC of 2.60 meq / g at 80°C compared to the membranes (IEC = 1.88 meq / g), but the conductivity was moderate at 80 mS / cm. Figure 11 shows the plot of lnσ vs. 1000 / T for all membranes. The hydroxide ion transport activation energy (E a ) was calculated from the slope of Figure 11 and was 9.33 to 15.28 kJ mol -1 These E a The value is 12.75 kJ mol for Nafion-117. -1 (Lin, B. et al., Chem. Mater. 22 (2010) 6718-6725).

[0125] The σ / IEC ratio is a measure of hydroxide ion mobility. By this metric, PNB-X 68 -Y32 Although PNB-X had a milder IEC, it had the highest hydroxide ion mobility (Table 1). 54 -Y 46 Although the hydroxide ion mobility of PNB-X was the highest, it was the lowest among the membranes (Table 1). Higher IEC would be expected to have higher mobility since it would increase the tendency for phase separation. 68 -Y 32 A possible explanation for the high anion mobility of PNB-X is its molecular weight. 68 -Y 32 The fact that the molecular weight of PNB-X is higher than that of the other samples indicates that 68 -Y 32 This was attributed to the lower water uptake and higher degree of chain entanglement compared to the other samples. The effect of molecular weight was particularly evident in PNB-X. 68 -Y 32 (the bottom row of Table 1) to the third and fourth columns (-Y 33 and -Y 38 ) is clear. The number of blocks is the same and the IEC values ​​are close (approximately 1.88 and 2.21). However, 68 -Y 32 For , the σ / IEC is nearly doubled because its block length is longer, which allows for better ion channel formation. Further studies are being conducted on the effect of molecular weight.

[0126] Water uptake (WU), hydration number (λ), number of freezable water molecules (N free ) and the number of bound unfreezable water molecules (N boundWater uptake is a crucial parameter that determines the conductivity and mechanical stability of AEMs. An appropriate amount of water is required for ionic hydration and conduction. However, excess water in the form of free water can cause membrane softening and channel flooding, leading to swelling and reduced performance of the membrane electrode assembly (MEA). Therefore, an optimal amount of bound water is required in the membrane to form an ionic solvent shell (Liu, L. et al., J. Polym. Sci. Part A: Polym. Chem. 56 (2018) 1395-1403; Liu, L. et al., J. Mater. Chem. A 4 (2016) 16233-16244; Liu, L. et al., J. Mater. Chem. A 6 (2018) 9000-9008). As shown in Table 1, the water uptake of the membrane increased with increasing IEC, reaching a maximum of 133.6%. PNB-X is the membrane with the best performance 68 -Y 32 had a WU of 63% and a conductivity of 122.7 mS / cm at 80°C. 54 -Y 46 had the highest IEC and therefore the highest WU of 133.6%, while PNB-X 68 -Y 32 The ionic conductivity was lower (80 mS / cm at 80 °C) than that of PNB-X. The hydration number (λ) is the number of water molecules per ionic head group. 54 -Y 46The high hydration number of 100 nm was the result of the presence of non-productive water and larger channel size. The interdomain distance was 86.4 nm as measured by SAXS. The amount of free water uptake increased with domain size, as shown in Table 1. More specifically, the number of unbound water molecules was found to track domain size. This indicates that non-productive free water can exist in ion channels when the ion channel is larger than the optimal size (Park, DY et al., J. Phys. Chem. C 117 (2013) 15468-15477). It has previously been shown that ion channels that are too small have low water uptake, resulting in reduced ion mobility and conductivity.

[0127] The number of freezable water molecules in the membrane (N free ) and the number of bound unfreezable water molecules (N bound Differential scanning calorimetry was used to measure the free water content, N. In a DSC thermogram, free water freezes just below 0°C. free can be obtained by subtracting the number of bound waters using the hydration number. The results for all membranes are shown in Table 1. PNB-X 68 -Y 32 In the case of free and N bound The amounts of bound water were 6.7 and 11.9, respectively. This was close to the optimal number of bound water molecules (9-10 per ion pair), as previously reported. Consequently, this membrane also showed the highest conductivity of 122.7 mS / cm at 80 °C. 54 -Y 46 In PNB-X, the conductivity decreased to 80 mS / cm at 80 °C due to the presence of more free water (10.6) and bound water (17.9), while IEC showed a decrease in conductivity to 80 mS / cm at 80 °C. 68 -Y 32 This can be attributed to the formation of excessively large ion-conducting channels, which were flooded with non-productive water. 74 -Y 26The free water uptake was lower (0.9) and not sufficient to support effective ion transport. Therefore, the conductivity was lower (61.3 mS / cm at 80 °C). 67 -Y 33 In the case of PNB-X, free water (7.8) was tolerated, but the higher bound water (12.1) resulted in a greater reduction in conductivity due to the larger number of hydration waters. 70 -Y 30 The lower free water (5.4) and higher bound water (13.3) in the membranes accounted for the lower ionic conductivity in the membranes.

[0128] Alkaline and thermal stability: Membrane durability is essential for a long operational life of electrochemical devices. An assessment of the alkaline stability of the current AEM was performed by immersing the membrane in 1 M NaOH solution at 80 °C. The loss in ionic conductivity was measured versus time for 1200 hours. As shown in Figure 12, no detectable loss in ionic conductivity (<1%) was observed over 1200 hours. Therefore, it can be concluded that non-hydrolyzable polymer backbones with cations tethered by long side chains exhibit adequate alkaline stability compared to hydrolyzable polymer backbones (e.g., polysulfones, polyketones, polyethers) and benzylic attachment of cations to the polymer chains.

[0129] The thermal stability of the membrane was studied by thermogravimetric analysis (TGA), as shown in Figure 13. Four decomposition stages were observed. The first stage, below 100 °C, was attributed to the loss of water from the membrane. The second stage, at approximately 250 °C, was attributed to the decomposition of the quaternary ammonium groups. The third stage, between 300 and 400 °C, resulted from the decomposition of alkyl side chains in the polymer. The fourth stage, above 400 °C, was attributed to the decomposition of the polymer backbone (Price, SC et al., Polym. Chem. 8 (2017) 5708-5717). These results suggest that the membrane was sufficiently stable under the operating conditions of a low-temperature AEM fuel cell or electrolyzer, which is typically operated below 80 °C.

[0130] Fuel cell test: PNB-X 62-Y 38 was selected for single-cell alkaline exchange membrane fuel cell testing due to its high ionic conductivity and excellent alkaline stability. The free-standing membrane was mechanically robust and withstood compression within the fuel cell hardware without damage.

[0131] The fuel cell was operated at 60 °C, which is comparable to many other AEMFCs found in the literature. The MEA underwent a break-in initiation procedure, where the cell was discharged at 0.5 V for 1 hour, followed by an additional 1 hour at 0.2 V. The anode and cathode dew points were set at 50 °C (69.51% RH) to avoid flooding the catalyst layer. The open circuit voltage (OCV) was found to be 1.028 V after break-in.

[0132] After an initial conditioning period, the moisture balance within the cell was optimized by adjusting the dew points of the humidified H2 and O2 streams at a constant cell voltage of 0.2 V. After each dew point adjustment, a discharge curve from open circuit to 0.2 V was recorded. Omasta et al. have previously found that proper water management is important for both the stability and performance of AEMFCs (Omasta, TJ et al., J. Power Sources 375 (2018) 205-213). Because the hydrogen oxidation reaction at the anode produces water, some of which diffuses through the AEM to hydrate the cathode, excessive water uptake (<100% RH) in the H2 inlet stream should be avoided. After adjusting the anode and cathode dew points, it was found that a dew point of 46°C (59.83% RH) for both the anode and cathode resulted in optimal stability and power output. As can be seen in Figure 14, the output was 542.57 mW / cm. 2 The peak power density is 0.43V and 1.26A / cm 2 When corrected for iR loss across the membrane (HFR = 123 mΩ cm 2 ), the iR corrected peak power density of the AEMFC is 713.04 mW / cm 2 This ohmic resistance was higher than the value reported by Omasta et al. (HFR = approximately 50 mΩ cm 2), due to non-optimized ionomer and catalyst layers, and may also be due to other factors, such as membrane thickness (t = 115 μm) and interfacial contact resistance. Nevertheless, these results are promising, and refinement of the MEA could lead to even higher performance.

[0133] In conclusion, a series of tetrablock copolymers containing all hydrocarbon backbones based on the vinyl addition polymerization of norbornene have been synthesized for anion exchange membranes. To the inventors' knowledge, this is the first anion exchange membrane based on vinyl addition polynorbornene. These membranes exhibited high thermal stability up to 400°C. PNB-X 68 -Y 32 The ionic conductivity is 122.7 mS / cm at 80°C, and the IEC (1.88 meq / g) is PNB-X. 54 -Y 46 (2.6 meq / g). This indicates the importance of optimizing the bound and unbound water content in the membrane. 68 -Y 32 The water uptake in PNB-X was measured by DSC analysis, and it was found that 6.7 unbound water molecules and 11.9 bound water molecules in the membrane resulted in the best ionic conductivity among the synthesized samples. Long-term alkaline stability testing in 1 M NaOH solution at 80°C showed exceptional chemical stability, with no detectable degradation (<1%) over 1200 hours. 62 -Y 38 was used to fabricate an MEA for alkaline fuel cell testing, with a voltage of 0.43 V and 1.26 A / cm 2 at 542.57mW / cm 2 Excellent performance was achieved with a peak power density of

[0134] Example 2 Highly conductive anion exchange membranes based on crosslinked poly(norbornene): vinyl addition polymerization Fuel cells are a clean energy conversion technology that has the potential to reduce the use of fossil fuels (Mekhilef, S. et al., Renewable Sustainable Energy Rev. 2012, 16, 981-989). Fuel cells can be used for stationary power generation, portable electronic devices, and transportation (Carrette, L. et al., Fuel Cells 2001, 1, 5-39; Winter, M. et al., Chem. Rev. 2004, 104, 4245-4269). Furthermore, fuel cells are environmentally friendly, easily refueled, and can have high energy conversion efficiency (Steele, B. C. et al., Nature 2001, 414, 345-352). Solid polymer electrolyte membranes, such as anion exchange membranes (AEMs) and proton exchange membranes (PEMs), simplify the fabrication of electrodes with three-phase boundaries because liquid / gas pressure balance is not required as in liquid electrolyte devices. High-pH AEMs have favorable oxygen reaction kinetics compared to acid-conducting PEMs, offering the opportunity for the use of non-precious metal catalysts and reducing fuel crossover (Varcoe, JR et al., Energy Environ. Sci. 2014, 7, 3135-3191; Lu, S. et al., Proc. Natl. Acad. Sci. USA 2008, 105, 20611-20614; Yu, EH et al., Energy Environ. Sci. 2012, 5, 5668-5680; Hickner, MA et al., J. Polym. Sci. Part B: Polym. Phys. 2013, 51, 1727-1735; Zhou, J. et al., J. Electrochem. Soc. 2013, 160, F573-F578).However, early membranes suffered from low ionic conductivity, poor chemical stability at high pH, ​​and high water uptake (Mohanty, AD et al., J. Mater. Chem. A 2014, 2, 17314-17320; Liu, L. et al., J. Mater. Chem. A 2016, 4, 16233-16244; Mandal, M. et al., J. Membr. Sci. 2019, 570-571, 394-402; Mohanty, AD et al., J. Electrochem. Soc. 2017, 164, F1279-F1285). More recently, higher conductivities (e.g., 100 mS / cm at 80°C) and chemical stability (in 1 M NaOH at 80°C) have been achieved by several researchers, as reviewed by Arges (Arges, CG et al. ACS Appl. Energy Mater. 2018, 1, 2991-3012). This significant advancement demonstrates that certain structural moieties can be used to address the deficiencies of past AEMs.

[0135] The structure of the polymer backbone, the location of the cations in the polymer structure, and the nature of the cations determine the conductivity and long-term alkaline stability of the AEM. Polymer backbones containing polysulfone, polyketone, and poly(aryl ether) moieties are susceptible to hydroxide ion attack and polymer backbone degradation (Zhang, X. et al., Polym. Chem. 2018, 9, 699-711; Shi, Q. et al., Polymer 2017, 121, 137-148; Weiber, EA et al., Polym. Chem. 2015, 6, 1986-1996; Akiyama, R. et al., Macromolecules 2016, 49, 4480-4489; Shimada, M. et al., J. Polym. Sci. Part A: Polym. Chem. 2016, 54, 935-944; Fujimoto, C. et al., J. Membr. Sci. 2012, 423-424, 438-449; Nunez, SA et al., ACS Macro Lett. 2013, 2, 49-52; Arges, CG et al., Proc. Natl. Acad. Sci. USA 2013, 110, 2490-2495). The problem of backbone degradation is mitigated by using polymers with all-hydrocarbon backbones and headgroup tethers. Cationic degradation can be mitigated by placing the headgroup at the end of long alkyl chain tethers, typically 4-6 carbons long (Long, H. et al., J. Phys. Chem. C 2012, 116, 9419-9426). Furthermore, alkyl tethers can isolate the cationic headgroup from the electron-withdrawing inductive effect of aromatic groups (if present) in the tether or polymer backbone.Thus, AEMs stable under realistic operating conditions (e.g., 80°C and 1 M KOH) can be synthesized by combining an all-hydrocarbon backbone with a cation tethered on a long alkyl chain (Lee, WH et al., ACS Macro Lett. 2015, 4, 453-457; Ono, H. et al., J. Mater. Chem. A 2017, 5, 24804-24812; Lee, WH et al., ACS Macro Lett. 2015, 4, 814-818).

[0136] In addition to alkaline stability, electrochemical devices require AEMs with high conductivity to minimize loss of ohmic resistance. Hydroxide ion conductivity is a function of ion mobility and ion exchange capacity (IEC). The IEC of AEMs is often maintained at a moderate value to avoid high water uptake, which can lead to membrane swelling and reduced ion mobility. Mobility can be improved by forming efficient ion-conducting channels (e.g., by using block copolymers) and by preventing excess water uptake in the membrane (Park, DY et al., J. Phys. Chem. C 2013, 117, 15468-15477). Thus, membranes attempting to achieve high IEC face the challenge of suffering from the consequences of ion-attracted water. Crosslinking can be used to address excess water uptake, but often at the expense of reduced ion mobility.

[0137] Phase separation within the block copolymer contributes to the formation of hydrophobic and hydrophilic regions within the polymer. The quaternary ammonium head groups within the hydrophilic phase are where hydroxide ion transport occurs. It is now clear that carbonate ion conductivity (relative to hydroxide ion conductivity) is crucial in AEMs due to the uptake of carbon dioxide from the ambient air. In fuel cells, carbon dioxide at the air cathode is readily absorbed and converts hydroxide ions produced at the cathode to bicarbonate or carbonate ions. When the bicarbonate or carbonate ions are transported to the hydrogen anode of the fuel cell, the generated carbon dioxide accumulates in the recycled hydrogen fuel along with water produced at the anode. Both carbon dioxide and water can diffuse back through the membrane to continue the hydroxide ion neutralization and carbonate ion migration process. Fuel cell testing using a fresh hydrogen supply avoids encountering this crucial issue of carbon dioxide accumulation and carbonate ion transport. Therefore, it is essential that the IEC and ion mobility are as high as possible for efficient carbonate ion transport. Carbonate ion mobility is significantly lower than hydroxide ion mobility.

[0138] One of the remaining challenges in designing stable, high-conductivity AEMs is water uptake. Excessive water uptake can occur at high IECs, flooding the channels and causing the membrane to swell. This leads to mechanical distortion and softening of the membrane. Materials with high IECs tend to adsorb large amounts of water. Some water is needed to form an ion-solvent shell and dilute hydroxide salts in the membrane. The absorbed water must be suitable for ion solvation, but excess free water is unproductive or undesirable. Therefore, water uptake can be divided into bound water (to form the solvent shell) and free water. Therefore, to obtain maximum ion mobility (i.e., conductivity) while maintaining the mechanical properties of the AEM, it is necessary to select an IEC that balances the amount of free and bound water in the membrane. Although this study did not address polymers with varying numbers of blocks, there is certainly an effect on conductivity (Chen, XC et al., Nano Lett. 2014, 14, 4058-4064; Inceoglu, S. et al., ACS Macro Lett. 2014, 3, 510-514; Sun, J. et al., J. Am. Chem. Soc. 2014, 136, 14990-14997; Sun, J. et al., Macromolecules 2016, 49, 3083-3090; Price, SC et al., Macromolecules 2013, 46, 7332-7340; Meek, KM et al., Macromolecules 2015, 48, 4850-4862).

[0139] Previous reports using vinyl-added poly(norbornene) in AEMs yielded very low conductivity (4 mS / cm at 80 °C) and showed a modest decrease in conductivity after immersion in 6 M NaOH at room temperature (He, X. et al., RSC Adv. 2015, 5, 63215-63225). The ion-exchange capacity (1.83 meq / g) was significantly lower than that reported in this literature, noting that the backbone was not a block copolymer and the headgroup tether contained ether linkages known to be susceptible to hydroxide ion attack. In another report, a block copolymer form of poly(norbornene) was synthesized by vinyl-addition polymerization for use as a pervaporation membrane (Kim, D.-G. et al., Chem. Mat. 2015, 27, 6791-6801). That form is not ionically conductive, does not have a tethered cationic head group, and does not face the same challenges of balancing ionic conductivity, water uptake, and chemical stability in base.

[0140] A strategy to avoid the problem of undesirable water swelling is to utilize cross-linking to increase mechanical stability. Several research groups have already reported the synthesis of crosslinked AEMs with improved alkali stability, dimensional stability, and expansion resistance (He, SQ et al., J. Membr. Sci. 2016, 509, 48-56; Xu, W. et al., Adv. Funct. Mater. 2015, 25, 2583-2589; Wang, J. et al., J. Membr. Sci. 2012, 415-416, 205-212; Tibbits, AC et al., J. Electrochem. Soc. 2015, 162, F1206-F1211; Gu, S. et al., Chem. Commun. 2011, 47, 2856-2858; Zhu, L. et al., Polym. Chem. 2016, 7, 2464-2475; Cheng, J. et al., J. Membr. Sci. 2016, 501, 100-108; Hu, EN et al., ACS Appl. Energy Mater. 2018, 1, 3479-3487). Many of these cases showed high hydroxide ion conductivity, but the reported AEMs did not have adequate long-term alkaline stability. Zhang et al. synthesized a crosslinked AEM with a hydroxide ion conductivity of approximately 200 mS / cm at 80 °C, but the long-term alkaline stability was not measured (Zhang, W. et al., J. Polym. Sci. Part A: Polym. Chem. 2018, 56, 618-625). Recently, Zhu et al. reported a cross-linked AEM with high ionic conductivity (200 mS / cm at 80 °C), but the membrane degraded by 27% when aged in 1 M NaOH solution at 80 °C for 500 h (Zhu, L. et al., Polym. Chem. 2016, 7, 2464-2475).Recently, Wang et al. synthesized an AEM with high conductivity (>200 mS / cm at 80 °C), but after 500 hours at 80 °C in a 1 M hydroxide ion solution, it lost 6.2% of its conductivity (Wang, L. et al., J. Mater. Chem. A 2018, 6, 15404-15412).

[0141] Achieving very high conductivity in fuel cell membranes requires additional considerations. Conductivity tests are often performed using only hydroxide ion conducting ions. Hydroxide ions can be produced in alkaline fuel cell cathodes under steady-state operating conditions, but carbonate ions rapidly form due to the accumulation of carbon dioxide in the recycled hydrogen at the anode. The only means to remove carbon dioxide is to vent unused hydrogen (a highly undesirable process) or to diffuse carbon dioxide back into the membrane, thereby converting hydroxide ions to carbonate ions. Therefore, under steady-state conditions, carbonate ion conductivity dominates. Carbonate ion mobility is significantly lower than hydroxide ion mobility. Therefore, extra conductivity is required.

[0142] This study explores the benefits of light polymer crosslinking as a means of implementing polymers with very high IEC while maintaining high hydroxide ion mobility (with proven stability) without excessive water uptake or membrane swelling. Poly(norbornene) is a preferred polymer backbone for low-cost AEMs due to its all-hydrocarbon backbone and the low cost of the starting material, dicyclopentadiene. This study demonstrates that light crosslinking can yield very high IEC polymers (by using low molecular weights for the norbornene monomer) and can be used to achieve record hydroxide ion conductivity. Poly(norbornene) can be polymerized via several different synthetic routes. This study explores the results of vinyl addition polymerization of norbornene. Results from ring-opening metathesis polymerization (ROMP) of norbornene are disclosed herein (Chen, W. et al., ACS Appl. Energy Mater. 2019). The synthesis methods and resulting properties of ROMP and vinyl addition polymers vary. It is worth noting that the glass transition temperature (T g). The inventors note that several types of ion-conducting polymers can be useful in electrochemical devices (e.g., fuel cells, electrolyzers, flow batteries). The membrane separating the two electrodes should have the highest possible ionic conductivity and low fuel crossover. The ionomer used to fabricate the electrodes should be compatible with the catalyst and electrode fabrication methods. An ion-conducting adhesive layer is also required between the electrode and the membrane. Therefore, ion-conducting polymers with different properties are of interest. Vinyl-addition polymerized norbornene has a high glass transition temperature (Grove, NR et al., J. Polym. Sci., Part B: Polym. Phys. 1999, 37, 3003-3010; Shin, B.-G. et al., Macromol. Res. 2007, 15, 185-190; Tetsuka, H. et al., Polym. J. 2009, 41, 643-649; Dorkenoo, KD et al., J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 797-803). Vinyl-addition poly(norbornene) itself has a T of 390°C. g whereas poly(hexylnorbornene) has a T of 265°C. g Various norbornene copolymers have a melting point of 340°C to 355°C. 47 203℃~331℃, 48 T 293℃~360℃ g and for poly(methylnorbornene) T exceeds 380°C. g It has been shown that

[0143] The vinyl addition polymerization route has previously been shown to produce AEM with high hydroxide ion conductivity (123 mS / cm) and excellent alkaline stability (<1% conductivity loss in 1,200 h at 80 °C in 1 M NaOH). For AEM, there is no compromise between block polydispersity, overall polymer molecular weight, and product yield. Tetrablock copolymers were chosen for this study because they have sufficiently high molecular weight and good yield. In this study, it was found that mild crosslinking of norbornene after polymerization extended the usable IEC range to very high values ​​without undesirable water uptake or swelling. To the best of our knowledge, the hydroxide ion conductivity reported here (198 mS / cm at 80 °C) is the highest reported value for a chemically stable polymer (in 1 M NaOH at 80 °C).

[0144] Materials: The chemicals used in this study are as follows: 1-Hexene, 5-bromo-1-pentene, and dicyclopentadiene were obtained from Alfa Aesar (used as received). Butylnorbornene (BuNB) and bromopropylnorbornene (BPNB) monomers were prepared by Diels-Alder reaction according to previously published procedures (Martinez-Arranz, S. et al., Macromolecules 2010, 43, 7482-7487). The monomers were purified by distillation over sodium with three freeze-degassing cycles. The synthesis reaction was carried out in a dry argon glove box, taking care to limit exposure to air and moisture. Toluene was heated to reflux over sodium and benzophenone for 6 hours to remove water. Freshly distilled toluene was used in the synthesis. Triisopropylphosphine and [(η 3 -allyl)Pd(Cl)]2 (Sigma-Aldrich) was used as received. (Allyl)palladium(triisopropylphosphine) chloride ((η 3 -allyl)Pd( iPrP)Cl) was used as a catalyst and was prepared as previously described (Lipian, J. et al., Macromolecules 2002, 35, 8969-8977). Lithium tetrakis(pentafluorophenyl)borate·(2.5EtO) (Li[FABA]) (Boulder Scientific Co.) was used as received. N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA), α,α,α-trifluorotoluene (TFT), anhydrous, ≥99%, and tetrahydrofuran (THF) (Sigma-Aldrich) were used as received.

[0145] Synthesis of tetrablock copolymer [poly(BuNB-b-BPNB-b-BuNB-b-BPNB)]: tetrablock PNB-X 34 -Y 66 (PNB = polynorbornene, X 34 = mole percent of combined hydrophobic blocks, Y 66 = mole percent of combined halogenated blocks) was prepared as described in Example 1. The catalyst was 3 -allyl)Pd( iThis polymer was prepared by dissolving Pr(P)Cl (26 mg, 0.074 mmol) and Li[FABA] (65 mg, 0.074 mmol) in 0.5 g of TFT and 0.5 g of toluene. Next, BuNB (0.28 g, 1.86 mmol) and toluene (6 mL) were added and stirred. The catalyst was added with vigorous stirring. The polymerization reaction of BuNB was completed in 10 min. The product was checked by gel permeation chromatography (GPC). BPNB (1.6 g, 7.44 mmol) and toluene (32 mL) were added to the catalyst-containing solution and stirred for 3 h to add the BPNB block to the BuNB block. After the BPNB was consumed, the product was checked by GPC analysis. The third block was formed by adding BuNB (0.28 g, 1.86 mmol) and toluene (6 mL) and allowing the reaction to proceed for 10 min. Finally, BPNB (1.6 g, 7.44 mmol) and toluene (32 mL) were added and stirred for 3 hours to form the fourth block on the polymer. The reaction product was quenched by precipitation in methanol. The polymer was purified over activated carbon and filtered to remove catalyst residues. The polymer product was precipitated twice in methanol and dried under vacuum at 60°C.

[0146] Nuclear Magnetic Resonance (NMR) and GPC: Polymers are 1 PNB-X was studied in CDCl3 using H NMR (Bruker Avance 400 MHz instrument). 34 -Y 66 Number average molecular weight (M n ) and polydispersity index (M w / M n ) was found by GPC (Shimadzu, equipped with an LC-20AD HPLC pump and a refractive index detector, RID-20A, 120V). GPC samples were loaded into THF with polystyrene standards at 30°C with an eluent flow rate of 1.0 mL / min.

[0147] Membrane casting and ion exchange: Tetrablock copolymer PNB-X 34 -Y 66(0.1 g) was dissolved in 5 mL of chloroform. When films were cast and reacted after casting, in situ crosslinking was performed by adding a crosslinker to the polymer / solvent mixture. The crosslinker, TMHDA, was added to the solution at different molar ratios relative to the moles of brominated monomer (i.e., monomer capable of forming a quaternary ammonium head group) in the polymer: 4 mol%, 5 mol%, 7 mol%, 10 mol%, 20 mol%, and 50 mol%. Crosslinker concentrations in this application are described in terms of the mole % of TMHDA crosslinker added to the polymer. For example, 5 mol% TMHDA means that up to 10% of the available head groups are consumed by the TMHDA crosslinker. It is noted that even if all the crosslinker reacts, the fraction of intramolecular versus intermolecular crosslinks would be difficult to assess. The solution was filtered through a 0.45 μm poly(tetrafluoroethylene) (PTFE) membrane syringe filter, and a film was cast and dried at 60° C. for 24 hours. The film was colorless, transparent, and flexible. The membrane was aminated by immersion in a 50 wt % aqueous trimethylamine solution (room temperature for 48 hours). The quaternized membrane was washed with DI water. Bromide ions were converted to hydroxide ions by immersing the membrane in a 1 M NaOH solution under nitrogen for 24 hours.

[0148] Hydroxide ion conductivity: Membrane conductivity was measured using four-point probe electrochemical impedance spectroscopy with a PAR2273 potentiostat. Membrane conductivity was measured in HPLC-grade water under a nitrogen atmosphere. The membrane was allowed to rest for 30 minutes before each measurement. In-plane ionic conductivity was calculated using Equation 1 below.

[0149]

number

[0150] In Equation 1, σ is the ionic conductivity (S / cm), L is the length between the sensing electrodes (cm), W and T are the width and thickness of the membrane (cm), respectively, and R is the resistance measured in ohms. Long-term (>1000 h) alkaline stability tests were performed by immersing the membrane in a 1 M NaOH solution at 80 °C in a Teflon-lined Parr reactor. Before each measurement, the membrane was removed from the solution and thoroughly washed with DI water. After each measurement, the membrane was stored in the reactor with freshly prepared NaOH solution. The change in ionic conductivity was used to evaluate long-term alkaline stability. During the measurements, each data point was measured in triplicate, and the average value was reported. The deviation of the measurements for each data point was <1%. Furthermore, alkaline stability was further analyzed by characterizing the chemical structure using a Nicolet 6700 FT-IR spectrometer.

[0151] Ion exchange capacity (IEC), water uptake (WU), number of freezable water molecules (N free ) and the number of bound unfreezable water molecules (N bound ), and hydration number (λ): 1 H NMR was performed on preaminated samples to determine the IEC of the membranes. Furthermore, titration was used to demonstrate that the quaternization reaction was quantitative. The titration involved converting the counteranion to chloride ions and then titrating the chloride ions present in the membranes. 1 It has been found that IEC measurements obtained by H NMR (pre-aminated sample) and titration (post-aminated sample) were identical (within experimental error). For example, PNB-X 67 -Y 33 The IEC of 1.90 meq / g and 1.92 meq / g were found by titration and NMR, respectively. The agreement indicates that each bromoalkyl group was quantitatively converted to a quaternary ammonium head group. That is, each available bromoalkyl group was reacted with trimethylamine. 1H NMR was found to be a more reliable method and is reported here for the materials. The water uptake of the membranes was calculated using Equation 2 below.

[0152]

number

[0153] In Equation 2, M d is the dry mass of the membrane, M w is the wet mass of the membrane after removing the surface water. - The number of water molecules per ionic group (λ) was calculated using Equation 3 below.

[0154]

number

[0155] The number of freezable water molecules per ion pair in the membrane (N free ) and the number of bound water molecules (N bound ) was found by differential scanning calorimetry (DSC). DSC measurements were performed on a Discovery DSC using an autosampler (TA Instruments). The film was hydrated and excess water was removed from the surface. 5–10 mg of sample was placed in a sealed DSC pan. The sample was cooled to −50°C and then heated to 30°C at a rate of 5°C / min under N2 (20 mL / min). The amounts of freezable and unfreezable water were calculated using the following equations 4 to 6 (Lue, SJ et al., J. Macromol. Sci. Part B: Phys. 2009, 48, 114-127; Mecheri, B. et al., J. Phys. Chem. C 2012, 116, 20820-20829; Moster, AL et al., J. Appl. Polym. Sci. 2009, 113, 243-250).

[0156]

number

[0157] M free is the mass of freezable water, and M tot is the total mass of water in the membrane. The weight fraction of freezable water was calculated using Equation 5 below.

[0158]

number

[0159] M w is the mass of the wet membrane, M d is the dry mass of the membrane. H f is the enthalpy found by integration of the DSC freezing peak, and H ice is the enthalpy of fusion of water corrected for freezing points below zero by Equation 6 below:

[0160]

number

[0161] ΔC p is the difference in specific heat capacity between liquid water and ice. ΔT f is the freezing point depression.

[0162] Small-angle X-ray scattering (SAXS): SAXS was used to analyze the phase separation of the block copolymer AEM. Hydrated films in the bromide ion form were tested in air using the NSLS-II beamline at the Center for Functional Nanomaterials (Brookhaven National Laboratory, Upton, NY). The wave vector (q) was calculated using Equation 7 below, where 2θ is the scattering angle.

[0163]

number

[0164] The characteristic separation length or interdomain distance (d) (i.e., Bragg spacing) was calculated by Equation 8 below.

[0165]

number

[0166] Fuel cell test: XL5-PNB-X 34 -Y 66 The membrane was selected for electrochemical testing in an alkaline electrolyte membrane fuel cell (AEMFC). The anode and cathode were fabricated using a slurry method as previously described. A low molecular weight form (20.5 kDa) of poly(BuNB-b-BPNB-b-BuNB) polymer was used as the ionomer based on results from a previous study (Ahlfield, J. et al., J. Electrochem. Soc. 2017, 164, F1648-F1653). The ionomer and Vulcan XC-72-supported 50% platinum catalyst were ground together in isopropanol. The catalyst / ionomer slurry was then sonicated at room temperature to ensure uniform mixing. The slurry was spray-coated onto 1% waterproof Toray TGPH-060 carbon paper and allowed to dry at ambient temperature. The platinum loading was 2.1 mg / cm. 2 and the ionomer to carbon ratio was 40%. This metal loading was intentionally used to avoid kinetic losses in non-optimized electrodes.

[0167] The membrane-electrode assembly was immersed in 1 M NaOH for 1.5 hours to convert bromide ions to hydroxide ions. A Fuel Cell Technologies test station with a single-pass serpentine graphite plate and PTFE gasket was used. Tests were conducted on a Scribner 850e fuel cell test station operated at 60°C using humidified H2 and O2 gases at 0.5 L / min each. The dew points of the anode and cathode gas streams were adjusted during the experiment.

[0168] Result: Catalyst (η 3 -allyl)Pd( i (PrP)Cl and two monomers, butylnorbornene (BuNB) and bromopropylnorbornene (BPNB), were prepared in a 1:1 ratio (η) sufficient to produce cationic Pd to initiate the polymerization. 3 -allyl)Pd( i The catalyst was synthesized using Pr(P)Cl and Li[FABA]. The BuNB to catalyst ratio was 25:1 ([M] / [Pd]=25). The reaction was allowed to proceed for 10 minutes. The second block of the tetrablock polymer was formed by adding BPNB at a monomer to catalyst ratio of 100:1 ([M] / [Pd]=100) and allowed to react for 3 hours. The final two blocks of the tetrablock polymer were synthesized by repeating the above two steps.

[0169] PNB-X 34 -Y 66 The number average molecular weights (M n ) were 5.17 kDa, 11.16 kDa, 5.34 kDa, and 10.68 kDa, respectively, based on GPC analysis of polymer samples extracted during synthesis according to Figure 15. n The molecular weight was 32.35 kDa and the polydispersity index (PDI) was 2.04.

[0170] The IEC is based on the terminal methyl protons (H) of the hydrophobic block, which resonate at 0.89 ppm. a ) and the methylene proton (H b ) by integrating 1 The results were evaluated by H NMR analysis. Because solution NMR is quantitative, 1 H NMR is a more accurate means of determining IEC. a and H b The integral ratio of H was used to calculate the IEC (Fig. 16). a :H bThe ratio was 1.55:2 as shown in Figure 16. This value was used to calculate the molar ratio of the hydrophobic block to the halogenated block, by recognizing the fact that the hydrophobic block has three methyl protons and the halogenated block has two methylene protons. 1 Using H NMR spectroscopy, the combined fractions of the hydrophobic and halogenated blocks were found to be 34 mol% and 66 mol%, respectively. The IEC was then calculated from the mass ratio of the two types of blocks. The IEC was calculated from the mass ratio of the block copolymer PNB-X in its hydroxide ion form without crosslinking. 34 -Y 66 The IEC was 3.46 meq / g. This IEC was slightly lower when crosslinker was added, as shown in Table 2. The IEC values ​​obtained by titration and NMR were previously found to be the same, indicating quantitative conversion of the bromoalkyl end groups to the quaternary ammonium form, as discussed above.

[0171] PNB-X, the precursor polymer 34 -Y 66 was crosslinked with N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) at different crosslinker concentrations (4-50 mol%) by adding specific mole percent of TMHDA relative to the total moles of halogenated monomers in the tetrablock polymer (Scheme 2). Without light crosslinking, the membranes were soft and could not be handled in membrane form without fracture. This result demonstrates one reason why the IEC of uncrosslinked polymers must be maintained at moderate values. High IEC values ​​do not result in usable membranes. Attempts to form and handle membranes without any crosslinking were unsuccessful because the membranes became too weak. Therefore, one direct benefit of light crosslinking was that usable high-IEC membranes could be fabricated and tested. Table 3 contains a summary of membrane properties.

[0172] [ka]

[0173] [Table 3] a OH - The conductivity was measured by a four-terminal conduction cell. b The IEC 1 Determined by 1 H NMR. c Ionic conductivity / IEC at 80°C. d The ionic ASR was calculated using the following formula: ASR=L / σ, where L=film thickness (cm) and σ=ionic conductivity (S / cm) (at 80° C.). e Water uptake was measured at room temperature. XL = crosslinked, PNB = polynorbornene. * The d-spacings were estimated by linear interpolation. X = hydrophobic block, Y = halogenated block. The subscripts indicate the molar ratio of each block.

[0174] Glass transition temperature (T g ): Vinyl-added poly(norbornene) copolymers have high T g (250℃-400℃). The addition of flexible alkyl side chains to the polymer T g DSC experiments were performed on the tetrablock copolymers used in this study. AEM samples were heated from 25°C to 400°C. However, below the decomposition temperature of the polymer (<300°C), T g The quaternary ammonium head group is known to decompose below 250°C. 12 The formation of ionic head groups and the absorption of water contribute to the T g The T of other forms (e.g., non-quaternized forms) of the polymer may affect g is not important.

[0175] Hydroxide ion conductivity (σ) and area specific resistance (ASR): High hydroxide ion conductivity is required for membranes used in electrochemical devices. Figure 17 shows the increase in conductivity at temperatures between 25°C and 80°C. This phenomenon is due to the greater thermal motion of ions at elevated temperatures (Li, Q. et al., Chem. Commun. 2014, 50, 2791-2793). The apparent activation energy (E a ) was estimated from the slope of ln(σ) vs. 1 / T and was found to be 11.7–14.9 kJ / mol. E a These values ​​are comparable to those of previously reported high-performance AEMs and PEMs, such as Nafion-117 (Dang, H.-S. et al., Macromolecules 2015, 48, 5742-5751; Pan, J. et al., Adv. Funct. Mater. 2010, 20, 312-319; Lin, B. et al., Chem. Mater. 2010, 22, 6718-6725).

[0176] Figure 18 shows the effect of crosslinker concentration on ionic conductivity. A high degree of crosslinking can stabilize the polymer membrane and inhibit excessive water swelling, but often at the expense of ionic mobility. It was observed that ionic conductivity increased slightly at a light crosslinking level of 5 mol% crosslinker concentration, and then decreased with higher crosslinking levels. XL5-PNB-X 34 -Y 66 (at a crosslinker concentration of 5 mol%), the hydroxide ion conductivity was 95.2 mS / cm and 198 mS / cm at 25°C and 80°C, respectively. 34 -Y 66The 4% crosslinker sample (50 mol %) had a lower ionic conductivity, 29 mS / cm and 74 mS / cm at 25°C and 80°C, respectively. Without crosslinking, the water uptake was so high that stable films could not be produced due to excessive swelling. A trend toward slightly lower conductivity and higher water uptake can be seen in the 4% crosslinker sample, but the water uptake values ​​are nearly the same for the 4% and 5% samples. At high crosslinker concentrations, the membranes are too densely crosslinked, limiting mechanical deformation and inhibiting ionic mobility.

[0177] The hydroxide ion conductivity normalized by IEC (σ / IEC) represents the mobility of hydroxide ions in the membrane. Hydroxide ion conductivity measures the average availability of cations in the membrane to contribute to hydroxide ion conduction. Because the IEC values ​​for each membrane are nearly identical (the mass change is due only to the added crosslinker), the hydroxide ion mobility follows the conductivity trajectory. The data in Table 3 are for XL5-PNB-X. 34 -Y 66 had the highest efficiency, while XL50-PNB-X 34 -Y 66 showed the lowest efficiency.

[0178] Finally, ionic ASR is a very important membrane metric. Based on the polymer conductivity and membrane thickness at 80°C, the ionic ASR was calculated using the following formula: ASR = L / σ, where L is the film thickness and σ is the ionic conductivity. 34 -Y 66 The ASR of the film is 0.032 ohm-cm 2 which is ≦0.04 ohm-cm 2 Meets the ARPA-E IONICS (Department of Energy, USA) target of 1000 kJ / cm². The ionic ASR values ​​of other membrane samples can be found in Table 3.

[0179] Water uptake (WU), hydration number (λ), number of freezable water molecules (N free ) and the number of bound unfreezable water molecules (N bound): For each polymer, there is an optimum amount of water uptake required for ion hydration and efficient channel conduction. Excess water in the form of free water can lead to excessive swelling of the ion-conducting channels and performance degradation due to membrane softening and channel flooding. As shown in Table 3, the WU of the membranes had a power law relationship with the crosslinker concentration. The membrane with the best performance, XL5-PNB-X 34 -Y 66 The XL4-PNB-X had a WU of 69.1% and a conductivity of 198 mS / cm at 80°C. 34 -Y 66 The membrane with the slightly lower crosslinker concentration had a slightly higher WU (73.7%) and also a lower conductivity (184 mS / cm at 80°C). The membrane with the highest crosslinker concentration, XL50-PNB-X 34 -Y 66 had the lowest WU (42%) due to its low ionic mobility and also had the lowest conductivity (74 mS / cm at 80°C).

[0180] The number of water molecules per ion pair (head group and mobile counterion) and the hydration number (λ) are determined by the number of water molecules that cannot be bound or frozen (N bound ) water, and unbound or freezable (N free ) water. The amount of each can be determined by DSC freezing point measurement. As shown in Table 3, the hydration number of the tested samples increased with decreasing crosslinker concentration, similar to WU. Bound water was calculated by subtracting free water from the hydration number. The results for all membranes are shown in Table 3. All of the membrane samples, regardless of their conductivity, had 6 to 7 bound water molecules per ion pair, while the number of free water molecules ranged from 0 to 6.20 per ion pair. The membrane with the highest conductivity (XL5-PNB-X 34 -Y 66 , 198 mS / cm at 80°C) is 5.21 N per ion pair free of water molecules and 6.00N bound On the other hand, the membrane with the lowest performance (XL50-PNB-X 34 -Y66 , 70.4 mS / cm at 80°C) is 0.00 N per ion pair in the membrane free and 7.40N bound The DSC curves for the samples with high and low crosslinking concentrations are shown in the Supporting Information (Figures 42-43). The enthalpy integrals of the peaks in the cooling curves are annotated in Figures 42-43. These peaks were used to calculate the number of freezable water molecules.

[0181] PNB-X 54 -Y 46 As shown in previous reports, water can freely exist in high IEC membranes without cross-linking, and the number of water molecules, N free and N bound can be as high as 10.6 and 17.9, respectively. At high crosslinking densities, the lack of flexibility in densely crosslinked membranes makes it increasingly difficult for water molecules, especially free water, to reside in the membrane. Non-crosslinked membranes that had less than six free water molecules per ion pair had conductivities below 70 mS / cm. XL50-PNB-X 34 -Y 66 The conductivity of the membrane was low due to the lack of free water. This indicates that some free water is essential for channel hydration and high ion mobility. The number of free water molecules also decreased with higher crosslinking density, likely due to limited connectivity between hydrophilic domains. The domain distance also showed little change for samples with different crosslinking densities. Therefore, optimization of the free and bound water molecules in the membrane is necessary to achieve maximum efficiency (Liu, L. et al., J. Polym. Sci. Part A: Polym. Chem. 2018, 56, 1395-1403; Liu, L. et al., J. Mater. Chem. A 2018, 6, 9000-9008).

[0182] Alkaline Stability: The long-term alkaline resistance of AEM is of particular interest for electrochemical devices operated at high pH and high temperature for thousands of hours. Stability measurements were performed by immersing the membrane in a freshly prepared 1 M NaOH solution at 80°C for over 1000 hours. Conductivity was measured periodically during the aging process. As shown in Figure 19 (left side), AEM was found to lose 1.22% to 1.40% conductivity over an aging period of >1000 hours. Each data point in Figure 19 is the average of three individual measurements. There was a deviation of <1% between the individual measurements for each data point. The three measurements differed only to the third significant digit. This conductivity loss value is low and acceptable for ARPA-E IONICS targets. PNB-X without crosslinking 68 -Y 32 The loss of conductivity for XL10-PNB-X containing 10 mol % crosslinker is 34 -Y 66 The loss in conductivity was 0.81%, compared to 1.22% for the uncrosslinked poly(norbornene) AEM. Although the loss in conductivity is slightly higher for the samples tested here compared to values ​​previously reported for uncrosslinked poly(norbornene) AEM, the crosslinked AEM in this study has a significantly higher IEC per ion pair and lower water uptake, resulting in a higher intramembrane pH than the uncrosslinked samples. Thus, although all samples were immersed in 1 M NaOH, the local hydroxide ion concentration in the membrane differs. The hydroxide ion concentration in the membrane is determined by λ, the number of hydroxide ions per water molecule. -1 This comparison shows that hydroxide ions are 68% more concentrated in the crosslinked AEM than in the previous non-crosslinked AEM. A lower WU per ion pair can create a more alkaline environment in the membrane, thereby accelerating decomposition. Further attempts were made to analyze the AEM for hydroxide ion decomposition. FTIR analysis of the chemical structure before and after alkaline aging showed no new peaks, as shown in Figure 19 (right side). -1 , 913cm -1 , 968cm -1 and 1060cm -1The C–N stretching frequency at 1000 kJ / cm indicates that the chemical structure of the film is indeed intact (Amel, A. et al., J. Electrochem. Soc. 2018, 165, F1133–F1138; Amel, A. et al., J. Electrochem. Soc. 2015, 162, F1047–F1055). However, FTIR is only semiquantitative, and structural changes at the 1% level are difficult to analyze by this method. Furthermore, quantitative solution NMR analysis is impossible because the sample is no longer soluble due to crosslinking.

[0183] Morphological Characterization: SAXS was used to study the phase separation and microstructure of crosslinked poly(norbornene) membranes. During casting, the poly(norbornene) block copolymer phase separates into ion-conducting channels based on the thermodynamic differences between the halogenated and hydrophobic blocks. Once crosslinking begins, the crosslinker further restricts self-assembly, thereby fixing the membrane's microstructure upon curing. The interdomain distance (d-spacing), or the average separation length between inhomogeneities in the membrane, was determined from the Bragg spacing of the first diffusion peak in the SAXS spectrum, as shown in Figure 20. The interdomain distance values ​​were determined by Lorentzian curve fitting and are listed in Table 3. The domain distances of polymers with different crosslinking densities were all found to be similar, ranging from only 48.6 to 51.8 nm. This differs from the domain distance of uncrosslinked membranes, which can range from 37.2 to 86.4 nm without any disorder.

[0184] Fuel cell test: XL5-PNB-X 34 -Y 66was selected for alkaline fuel cell demonstration because it had high ionic conductivity and was chemically stable. The membrane was mechanically robust and easily integrated into fuel cell hardware. Fuel cell testing was conducted at a typical operating temperature of 60°C. The fuel cell was first conditioned at a cell voltage of 0.5 V for 1 hour, followed by conditioning at 0.2 V for 1 hour. After conditioning, the open-circuit voltage (OCV) was 1.042 V. Current-voltage voltammograms and impedance spectra at 0.4 V were recorded periodically. The dew points of the anode and cathode feed gases were set at 52°C (i.e., 74.8% RH) and 56°C (i.e., 86.6% RH), respectively.

[0185] Figure 21 shows the cell voltage and power output as a function of current density. The peak power density was 0.534 V and 954 mA / cm. 2 510mW / cm 2 Figure 21 also shows the voltage as a function of current density after correcting for the iR drop across the membrane. The membrane resistance was 95 mΩ cm, as obtained from the high frequency intercept of the impedance plot. 2 The iR correction cell output was 573mW / cm 2 The output power was 2 W / cm reported by Wang et al. 2 Although this is mild compared to the previous cell, the membrane electrode assembly used here was not optimized for ionomer and catalyst layer content, so the operating temperature was lower (60 °C here versus 80 °C according to Wang et al.) and the membrane was 64 μm thicker than required (Wang, L. et al., J. Mater. Chem. A 2018, 6, 15404-15412). These fuel cell results demonstrate that membranes can be successfully integrated into working electrochemical devices.

[0186] In summary, crosslinked anion-conducting polymers synthesized by vinyl addition polymerization of norbornene were studied. The membranes possessed very high ionic conductivities, up to 198 mS / cm, at 80°C. It was found that only light crosslinking was necessary to alleviate the water swelling problem that plagued other high-IEC AEMs. Light crosslinking was sufficient to avoid the problems encountered with highly crosslinked AEMs. Dimensional stability was attributed to crosslink density, which can be adjusted to balance the free and bound water content in the membrane. In the optimized membrane, there were 5.21 free water molecules and 6.00 bound water molecules per ion pair. Excellent alkaline stability in 1 M NaOH solution at 80°C was demonstrated (<1.5% conductivity loss in >1000 hours at 80°C). Hydrogen / oxygen fuel cell testing at 60°C yielded a current of 0.534 V and 954 mA / cm. 2 510mW / cm 2 These tetrablock copolymers, with their very high ionic conductivity and alkaline resilience, are excellent candidates for high performance electrochemical devices.

[0187] Example 3 Highly conductive anion exchange membranes based on crosslinked poly(norbornene): Ring-opening metathesis polymerization Because various monomers can be synthesized via the Diels-Alder reaction, poly(norbornene) is an attractive polymer backbone for AEM (Yang, Z. et al., Polymer 2008, 49, 5128-5136). The low molecular weight of norbornene monomers allows for high IEC. Norbornene can be polymerized via vinyl addition polymerization or ring-opening metathesis polymerization (ROMP). Coates et al. performed ROMP of dicyclopentadiene and tetraalkylammonium-functionalized norbornene to synthesize an AEM with a hydroxide ion conductivity of 18 mS / cm and an IEC of 1.4 meq / g at 20 °C (Clark, TJ et al., J. Am. Chem. Soc. 2009, 131, 12888-12889). The polymer was crosslinked via a metal cation-based route using a bis(terpyridine)Ru(II) complex. The resulting hydroxide ion conductivity was 28.6 mS / cm at 30°C, with an IEC of 1.4 meq / g (Zha, Y. et al., J. Am. Chem. Soc. 2012, 134, 4493-4496; Wang, C. et al., J. Membr. Sci. 2018, 556, 118-125). In studies to enhance conductivity, the IEC was increased and crosslinking was introduced to enhance its properties. Wang et al. reported an alkyl-bridged AEM with an IEC of 2.89 meq / g and a resulting hydroxide ion conductivity of 64.79 mS / cm at 25°C, but no long-term alkaline stability was demonstrated. The IEC of 2.79 meq / g and an OH conductivity of 40 mS / cm at 30°C were also reported. -Conductive diphenyloxide-crosslinked AEMs exhibited poor alkaline stability (34% conductivity loss after immersion in 2 M NaOH at 50 °C for 16 days) along with material brittleness (Wang, C. et al., Macromol. Mater. Eng. 2018, 303, 1700462). Another hydrogenated poly(norbornene) membrane with ether linkages and flexible tethers was prepared by Price et al. (Price, SC et al., Polym. Chem. 2017, 8, 5708-5717). The resulting conductivity was 69 mS / cm at 20 °C and 133 mS / cm at 80 °C. However, after immersion in 0.1 M NaOH at 90 °C for 239 hours, the conductivity decreased by approximately 50%. In summary, state-of-the-art AEMs based on poly(norbornene) prepared by ROMP generally exhibited low conductivity and / or poor long-term alkaline stability.

[0188] In this study, AEMs with all-hydrocarbon backbones were produced by two different synthetic routes using bromopropylnorbornene (BPNB) and butylnorbornene (BuNB). Both vinyl addition polymerization and ROMP routes were investigated. ROMP of norbornene homopolymers and diblock copolymers, as well as flexible alkyl tethers and trimethylammonium cations, was disclosed and used in this study. The combination of a hydrocarbon poly(norbornene) backbone and tethered quaternary ammonium headgroups was shown to provide excellent alkaline stability and high ionic conductivity. In this study, polymers with high IECs up to 4.73 meq / g were synthesized and cast into membranes using N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) as a crosslinker. Consequently, conductivities of 99 mS / cm at 25°C and 195 mS / cm at 80°C were achieved after 792 h in 1 M NaOH at 80°C, without any loss of conductivity. This is higher than the hydroxide ion conductivity of membranes previously reported for chemically stable AEMs at 80°C.

[0189] Materials: Dicyclopentadiene, 5-bromo-1-pentene, and 1-hexene were purchased from Alfa Aesar and used as received. Functionalized monomers, i.e., bromopropylnorbornene (BPNB) and butylnorbornene (BuNB), were synthesized as previously described (Martinez-Arranz, S. et al., Macromolecules 2010, 43, 7482-7487; Mandal, M. et al., J. Membr. Sci. 2019, 570-571, 394-402). Polymerization was carried out in a glovebox (dry nitrogen atmosphere) to avoid moisture and air. Prior to polymerization, the monomers were purified by distillation over sodium and degassed by three freeze-degassing cycles. Tetrahydrofuran (THF), dichloromethane (anhydrous, DCM), sodium bicarbonate (NaHCO3), methanol, tosylhydrazide, sodium hydroxide, N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA), ethyl vinyl ether, trimethylamine solution (TMA, 50 wt%), and toluene were purchased from Sigma-Aldrich and used as received. Grubbs third-generation catalyst (Grubbs third generation, G3) was synthesized from Grubbs second-generation catalyst (purchased from Sigma-Aldrich) and pyridine (Bates, C.M. et al., Macromolecules 2015, 48, 4967-4973).

[0190] Synthesis of diblock copolymer and poly(BPNB) homopolymer: Poly(BuNB-b-BPNB) diblock copolymer was synthesized by sequential addition of monomers in a glove box at room temperature as shown in Scheme 3. The material was rPNB-X. m -Y n (rPNB represents norbornene by ROMP, X and Y are the hydrophobic BuNB and hydrophilic BPNB monomers in the polymer, respectively, and m and n are the 1 (The mole % of BuNB and BPNB monomers are calculated by H NMR.) The homopolymer is rPNBY100 and rPNB-LY 100 (Y 100 represents the homopolymer of BPNB, and LY 100 represents a homopolymer of BPNB with a higher molecular weight).

[0191] [ka]

[0192] All monomers were purified by distillation and degassing using three freeze-pump cycles prior to polymerization. Grubbs 3rd generation was dissolved in DCM to prepare a 0.01 g / ml solution and then stirred for 10 minutes. A monomer solution (0.01 M) was obtained by dissolving BuNB or BPNB in ​​DCM and stirring for 10 minutes. To prepare the first block, poly(BPNB), the catalyst solution was injected into the BPNB monomer solution with vigorous stirring. After a 10-minute reaction time, the BPNB polymerization was complete. A small aliquot was removed and quenched with ethyl vinyl ether for gel permeation chromatography (GPC) analysis. Next, to attach the BuNB block onto poly(BPNB), the BuNB solution was added to the reaction solution and stirred for 5 minutes. After the reaction was complete, ethyl vinyl ether was added to the reaction mixture to quench the polymerization. The mixture was stirred for 30 minutes. The excess solvent was evaporated in air, and the concentrated polymer solution was precipitated in methanol. The resulting product was precipitated twice in methanol and dried overnight at room temperature. The procedure for poly(BPNB) homopolymer was similar to that for the diblock polymer, except for the addition of a second BuNB block.

[0193] Hydrogenation of double bonds: The unsaturated polymer (0.4 g) prepared by ROMP was dissolved in toluene (50 mL) at room temperature in a two-neck round-bottom flask equipped with a reflux condenser (Hayes, C.O. Directly-Patternable Benzocyclobutene Dielectric Materials. Ph.D. Thesis, The University of Texas at Austin, Texas, USA, 2016; Yoon, K.-H. et al., Polymer 2012, 53, 2290-229). A stoichiometric amount of tosylhydrazide (1:6 ratio of double bond to hydrazide) was added to the polymer solution. The solution was purged with nitrogen gas for 30 minutes to remove dissolved oxygen. The mixture was stirred under nitrogen gas at 110 °C for 24 hours. The solution was then cooled to room temperature and washed three times with saturated NaHCO3 solution (500 mL each time) until the reaction solution became clear. The polymer solution was concentrated by removing toluene overnight at room temperature and the product was precipitated in methanol.

[0194] Preparation of crosslinked AEM: The hydrogenated polymer (0.15 g) was dissolved in 6 mL of toluene. The crosslinking reagent, TMHDA, was dissolved in 1.5 mL of toluene and added to the polymer solution. The mixture was stirred at room temperature for 30 minutes, then filtered through a 0.45 μm poly(tetrafluoroethylene) membrane syringe filter and placed in an aluminum dish. The solution was dried at 60 °C for 24 hours, by which time the crosslinking reaction was complete. The term "crosslinker concentration" refers to the mole percent of crosslinking compound (i.e., TMHDA) added to the polymer mixture relative to the number of crosslinkable sites in the polymer. It was determined that the crosslinker could completely react with sites on the polymer, but it was not determined what fraction of the crosslinking reaction occurred between intramolecular sites versus intermolecular sites. The film was peeled from the aluminum dish and immersed in TMA at room temperature for 48 hours to quaternize the bromopropyl head groups. The quaternized film in the bromide ion form was thoroughly washed with DI water and Br - ions to OH -To convert the ions, the membranes were immersed in 1 M NaOH under nitrogen for 24 hours. The cross-linked AEMs were XLp-rPNB-X for the diblock and homopolymer membranes, respectively. m -Y n and XLp-rPNB-Y 100 where XL stands for cross-linking and p is the cross-linker concentration.

[0195] Material characterization: 1 H NMR spectroscopy was performed using a Bruker Avance 400 MHz NMR spectrometer, tetramethylsilane as an internal standard, and CDCl3 as the solvent. The number average molecular weight (M n ) and polydispersity index (M w / M n ) were obtained by GPC analysis (Shimadzu) equipped with an LC-20CE HPLC pump and a refractive index detector (RID-20A, 120V). All measurements were performed in THF with the eluent at 1.0 mL min -1 The measurements were performed at 30°C using a flow rate of 1000 kJ / min. Standard polystyrene was used. In-plane hydroxide ion conductivity was measured using a PAR2273 potentiostat with four-electrode probes and electrochemical impedance spectroscopy (1 Hz to 1 MHz). A nitrogen purge was used with HPLC-grade water. Water uptake (WU), swelling ratio (SR), and hydration number (λ) were determined as described in the package insert. Bound water number (unfreezable, N bound ) and the number of freezable water molecules (N free ) was determined by differential scanning calorimetry (DSC). DSC measurements were performed on a Discovery DSC using an autosampler (TA Instruments). bound and N free To determine the glass transition temperature (T), fully hydrated films (5–10 mg) with no surface water were placed in an aluminum pan, sealed, cooled to −50°C, and then heated to 30°C at a rate of 5°C / min under a 20 mL / min N2 flow. gDSC was also used to measure the T g The material was subjected to a temperature cycle from 20°C to 200°C to obtain

[0196] Thermogravimetric analysis (TGA) was performed on a TA Instruments Q50 analyzer using 5–10 mg of dried membrane in bromide ion form. The temperature was increased from room temperature to 800 °C at a heating rate of 10 °C / min in a nitrogen atmosphere. The mechanical properties of fully hydrated and dried membranes were measured using a SANS CMT8102 tensile tester (Xinsansi Co., China) at a stretching rate of 5 mm / min. Alkaline stability was tested by immersing the AEM in a 1 M NaOH solution at 80 °C in a Teflon-lined Parr reactor. The conductivity of the treated AEM was measured at 25 °C versus time after complete removal of residual NaOH. Furthermore, to further confirm the chemical structure, the AEM was also studied by FTIR before and after alkali treatment.

[0197] Transmission electron microscopy (TEM): TEM is used to qualitatively observe the phase-separated microstructure of a membrane. - The experiments were performed on dried AEM samples in the form of a membrane. Each membrane was embedded in epoxy and sectioned using a Microtone. The membranes were then immersed in a NaI solution (2.0 M) at 80 °C for 2 days to obtain I. - and measured using a JEOL JEM-2000EX microscope (Lee, KH et al., Energy Environ. Sci. 2017, 10, 275-285).

[0198] Small angle X-ray scattering (SAXS): SAXS was also used to analyze the phase separation of the block copolymer AEM. Hydrated films in the bromide ion form were tested in air using the NSLS-II beamline at the Center for Functional Nanomaterials (Brookhaven National Laboratory, Upton, NY). The wave vector (q) was calculated using Equation 1 below, where 2θ is the scattering angle.

[0199]

number

[0200] The characteristic separation length or interdomain distance (d) (i.e., Bragg spacing) was calculated using Equation 2 below.

[0201]

number

[0202] H2 / O2 Fuel Cell Measurements: AEM anodes and cathodes were fabricated by a previously used slurry method and were identical in composition (Ahlfield, J. et al., J. Electrochem. Soc. 2017, 164, F1648-F1653). First, a lower molecular weight (20.5 kDa) poly(norbornene) ionomer powder was synthesized according to previous work. The dried ionomer powder and Vulcan XC-72 (carbon)-supported 50% platinum catalyst were ground together in isopropyl alcohol (IPA) using a mortar and pestle to achieve a slurry suitable for spraying. After sonication for 30 minutes, the homogenized catalyst and ionomer slurry was sprayed onto 1% waterproof Toray TGPH-060 carbon paper and allowed to dry at room temperature for 24 hours. The metal loading on the electrode was approximately 2.1 mg / cm. 2A 40% ionomer / carbon ratio was used. The electrodes were pre-treated with OH by immersion in 1 M NaOH for 2 hours with a N purge. - The NaOH solution was refreshed every 20 minutes. The electrodes and ROMP poly(norbornene) diblock AEM were placed in Fuel Cell Technologies hardware for testing at 60 °C in a Scribner 850e fuel cell test station. H2 and O2 feed gas (0.5 L min-1) were added. -1 The dew point of the fuel cell was adjusted throughout the test to optimize the water balance within the fuel cell.

[0203] Experimental results: rPNB-X m -Y n Diblock copolymer and rPNB-Y 100 / rPNB-LY 100 A hydrophilic homopolymer (poly(BPNB)) was synthesized in this study. The monomers (BuNB and BPNB) were prepared according to previous studies. The Grubbs third generation catalyst (G3) was synthesized from the Grubbs second generation catalyst and pyridine. To grow the diblock copolymer, BPNB ([M] / [G3] = 100:1) was reacted for 10 minutes, and BuNB ([M] / [G3] = 20:1) was reacted for 5 minutes. The polymerization time was optimized for the individual monomer additions and their feed ratios. To demonstrate the sequential growth of each block during the formation of the diblock copolymer, Figure 22 shows the rPNB-X 60 -Y 40 A representative GPC trace of M is shown. After completion of the first block, n is 18.34 kDa, and M n / M w The addition of the second monomer resulted in a higher M of 24.68 kg / mol. n and 2.19 M n / M w GPC traces of the diblock copolymer before and after hydrogenation showed similar trends and M n(24.68 vs. 25.96 kg / mol), indicating that no side reactions occurred during the hydrogenation. n The values ​​were kept constant to study the relationship between different copolymers. 100 ) had poor mechanical properties. Therefore, as shown in Table 4, the higher M n Homopolymer of (rPNB-LY 100 ) was also synthesized. For a [BPNB] / [G3] ratio of 200:1, the length consisted of 129 repeating units (25 min reaction time). Higher molecular weight homopolymers were produced by using a higher BPNB to G3 ratio (i.e., 500:1) and extending the reaction time to 2 h. The resulting homopolymer had 198 repeating units.

[0204] [Table 4] a Calculated from the monomer feed ratio. b GPC results. c mol% and IEC are 1 Determined by 1 H NMR. d GPC data in THF vs. standard polystyrene.

[0205] of diblock copolymer before and after hydrogenation 1 The H NMR spectrum is shown in Figure 23. 5.33 ppm (H a ) arises from the protons at the double bonds on the polymer backbone. The characteristic signal of the protons at the terminal methyl groups of the butyl side chains is at 0.89 ppm (H c ) and the methylene proton (-CHBr) adjacent to the bromine atom in the bromopropyl side chain is present at 3.40 ppm (H b The molar ratio of BuNB to BPNB blocks (R) is c and H b NMR integral ratio of protons (R = 2I(H c ) / 3I(H b)) was calculated by comparing OH - The IEC value of the polymer in the form NMR = 1000 / (150R + 213), where 150 and 213 are the quaternized BPNB (OH) and quaternized BPNB (OH), respectively. - The molecular weight of the repeating unit of the polymer. NMR ranged from 2.31 to 4.73 meq / g (Table 4).

[0206] The carbon-carbon double bonds in the poly(norbornene) backbone were hydrogenated to improve the chemical stability of the polymer (Zhu, T. et al., Angew. Chem., Int. Ed. 2018, 57, 2388-2392). After hydrogenation, the NMR peaks corresponding to the protons in the double bonds (H a ) was not present, indicating complete hydrogenation of the double bond.

[0207] Microphase separation: The separation of hydrophilic and hydrophobic domains of the crosslinked polymer was studied by SAXS and TEM (Figures 24 and 25, respectively). The interdomain distance (d) was established to be 2π / q and is listed in Table 5. Crosslinked diblock rPNB-X 60 -Y 40 Well-resolved peaks were observed in the films. When the cross-linker concentration was changed from 10 mol% to 45 mol%, the SAXS peaks increased from 0.08 nm to 1.08 nm. -1 to 0.10 nm -1 This corresponds to a decrease in domain size (d) from 78.64 nm to 62.71 nm (Table 5). This suggests that the higher crosslinker concentration slightly narrows the size of the ion channel. 60 -Y 40 Close examination of the XL-rPNB-X shows that there are two peaks and the q-vector ratio is 1:2, indicating a layered polymer morphology. 22 -Y 78 The film had only one peak at a higher q value (approximately 0.30 nm -1) This corresponds to a smaller domain size (approximately 21 nm) and less microphase separation. These results are consistent with the TEM images shown in Figure 25, where the dark regions correspond to hydrophilic domains and the lighter regions correspond to hydrophobic domains.

[0208] [Table 5] XL is the crosslinker concentration. IEC is 1 Calculated based on H NMR (including mass of TMHDA). λ is the hydration number. N free is the number of water molecules that can be frozen. N bound is the number of bound non-freezable water molecules. SR is the swelling ratio. d-spacings (nm) were calculated from SAXS data.

[0209] As expected, the homopolymer XL-rPNB-LY 100 showed minimal signs of phase separation. Only one weak peak (forming a shoulder in SAXS) was observed. These small peaks are attributed to isolated ion clusters, as shown in Figure 24. This lack of apparent phase separation contrasts with the results of block copolymers, which can be very effective in creating phase-separated, high-mobility ion-conducting channels. This was also concluded in the literature for vinyl-added poly(norbornene). When the crosslinker concentration was increased from 15 mol% to 25 mol%, the size of the ion clusters decreased from 25.68 nm to 23.05 nm, which is larger than that of AEM, which has a low IEC value (Chen, W. et al., J. Membr. Sci. 2016, 514, 613-621; Wu, X. et al., J. Mater. Chem. A 2014, 2, 12222-12231).

[0210] 3.1.9. Ion Exchange Capacity (IEC) and Water Uptake (WU): High IEC can contribute to high anion conductivity in the membrane, which leads to ionization of anion-cation pairs and high anion mobility. Unfortunately, high IEC can also lead to high and unacceptable water uptake, potentially flooding the ion channels and reducing hydroxide ion mobility. The IEC of the polymers in this study varied from 2.31 to 4.73 meq / g, as shown in Table 4. The relatively low molecular weight of bromopropylnorbornene allowed for the synthesis of all-hydrocarbon polymer backbones with very high IEC. Lower crosslinking degrees generally tend to result in higher WU. Polymers with high IEC and low crosslinker concentrations were soluble in aqueous TMA solutions during amination. Therefore, the focus of this study is on crosslinked polymers.

[0211] WU is required for ion solvation and conduction. As shown in Figure 26, there is a general correlation between WU and swelling ratio for a specific polymer backbone at a specific crosslinker concentration. WU has a higher inverse correlation with crosslinking. WU also correlates with IEC (at the same crosslinker concentration), but to a lesser extent than crosslinking. For each series of AEM, WU values ​​were similar for the same crosslinker concentration. For example, at a crosslinker concentration of 20 mol%, the highest water uptake was observed for XL20-rPNB-X. 22 -Y 78 The lowest value was 157% of that of XL20-rPNB-LY (3.78 meq / g). 100 However, for AEMs based on the same polymer, the WU changed dramatically with crosslinker concentration. For example, for XL-rPNB-LY, 100 showed the lowest WU of 79% at a cross-linker concentration of 25 mol%, while the highest WU was 224% at a cross-linker concentration of 15 mol%. For all prepared AEMs, the WU varied from 40% to 400%, and the swelling ratio varied from 18% to 53% at room temperature. Due to the fragility of the membranes, XL-rPNB-Y 100 It was not possible to test the expansion ratio of the AEM.

[0212] The hydration number (λ), which is the average number of water molecules per ion pair per polymer, is listed in Table 5. Figure 26 shows the solvation degree of each ion pair within the polymer to crosslinker concentration. The solvation degree of different AEMs (i.e., XL-rPNB-X) at similar molecular weights and crosslinker concentrations was also observed. 60 -Y 40 , XL-rPNB-X 22 -Y 78 and XL-rPNB-Y 100 The λ values ​​of the diblocks XL-rPNB-X with the lowest IEC were analyzed. 60 -Y 40 The AEM of XL-rPNB-X had the highest λ value compared to the other two AEMs. 60 -Y 40 This indicates that the well-ordered hydrophilic lamellar domains of XL-rPNB-Y facilitate water uptake. 100 had the lowest λ, indicating that the ion channel did not expand as readily as the others.

[0213] The hydration number is determined by DSC freezing point measurement to determine the number of freezable (or free) water molecules (N free ) and the number of bound water molecules (N bound ) was further analyzed. The higher the cross-linking degree, the free and N bound Both water and water were reduced, which is consistent with established trends. For each polymer, there is an optimal crosslinker concentration to achieve the highest mobility. Insufficient WU (i.e., high crosslinker concentration) results in low mobility, while excessive WU (low crosslinker concentration) can flood the ion channel (Liu, L. et al., J. Mater. Chem. A 2018, 6, 9000-9008). For example, XL15-rPNB-LY 100 (15 mol% crosslinker concentration) is 4.98 N free and 22.31 N boundThe high WU flooded the ion channels and diluted the hydroxide ions, resulting in a conductivity of only 75 mS / cm and a relatively low ion mobility as measured by σ / IEC = 31.14. Increasing the crosslinker concentration from 15 mol% to 20 mol% resulted in approximately the same N free (5.68) as a result, but N bound was lower (8.48), thereby resulting in a higher conductivity of 99 mS / cm at 25 °C. The increased conductivity is attributed to a higher ionic mobility of σ / IEC = 43.24. Further increasing the cross-linker concentration to 25 mol% resulted in a higher N free = 3.72 and N bound This resulted in an insufficient WU with σ / IEC = 6.14. This level of WU was not very effective in terms of mobility, with σ / IEC reduced to 33.71. The results are similar to those of the sample with a 15 mol% crosslinker concentration.

[0214] XL35-rPNB-X, the diblock AEM with the highest conductivity 60 -Y 40 and XL20-rPNB-X 22 -Y 78 is similar to N free (5.76 and 6.59 respectively) and N bound (19.49 and 16.48, respectively). However, the lowest N free (5.68) and N bound (8.48) with the homopolymer (XL20-rPNB-LY 100 ) had the highest conductivity of all AEMs. The mobility was high, as evidenced by σ / IEC = 43.24. This indicates that the ROMP homopolymer with a crosslinker concentration of 20 mol% effectively utilized WU without flooding the channel with water, suitable for high mobility.

[0215] Conductivity versus cross-linker concentration data is summarized in Figure 27. Hydroxide ion mobility (and hydroxide ion conductivity) is highly affected by the amount of cross-linker. As the amount of cross-linker in the sample increases, the conductivity decreases.100 XL20-rPNB-Y showed a peak of 103 mS / cm (at 25°C) at a cross-linker concentration of 20 mol%. 100 Although XL20-rPNB-LY had the highest conductivity of all AEMs reported in this study, its mechanical properties were poor. 100 The conductivity was improved by increasing the molecular weight of the polymer, and the polymer had excellent conductivity (99 mS / cm at 25 °C and 195 mS / cm at 80 °C). The conductivity reported here is higher than that reported in the literature for ROMP-based AEM, which is largely due to the high IEC value of poly(norbornene) (Zhao, Y. et al., Int. J. Hydrogen Energy 2016, 41, 16264-16274).

[0216] Hydroxide ion transport activation energy (E a ) (Li, X. et al., ACS Appl. Mater. Interfaces 2014, 6, 7585-95; Chen, W. et al., J. Mater. Chem. A 2017, 5, 15038-15047) were calculated and are shown in Figure 27. 60 -Y 40 As the cross-linker concentration increases from 10 mol% to 45 mol%, E a The ion exchange rate (IEE) increased from 9.46 kJ / mol to 13.25 kJ / mol. 100 and XL20-rPNB-X 22 -Y 78 ) then, those E a The values ​​are nearly identical (10.94 kJ / mol and 10.40 kJ / mol, respectively), indicating that the hydroxide ion environments of the AEMs are similar.

[0217] A different way to examine the data is to plot the conductivity as a function of λ at 25°C, as shown in Figure 28. Figure 28 shows regions of insufficient water (low λ) and excess swelling (high λ). High λ values ​​flood the ion channels and reduce conductivity. For λ < 20, the homopolymer AEM exhibits a higher conductivity than the diblock AEM (XL-rPNB-X). 22 -Y 78 and XL-rPNB-X 60 -Y 40 ) had a relatively high conductivity compared to XL20-rPNB-LY. 100 (λ=14) has a hydroxide ion conductivity of 99 mS / cm, and XL40-rPNB-X 22 -Y 78 had a conductivity of 77 mS / cm. Comparisons with other AEMs have been reported in the literature (Liu, L. et al., J. Mater. Chem. A 2016, 4, 16233-16244; Zhu, M. et al., J. Membr. Sci. 2018, 554, 264-273; Zhang, M., et al., ACS Appl. Mater. Interfaces 2016, 8, 23321-23330; Abouza-ri-lotf, E. et al., J. Mater. Chem. A 2017, 5, 15326-15341; Olsson, J. S. et al., Adv. Funct. Mater. 2018, 28, 1702758; He, G. et al., ACS Appl. Mater. Interfaces 2017, 9, 28346-28354; Zhang, X. et al., Polym. Chem. 2018, 9, 699-711; Olsson, JS et al., Macromolecules 2017, 50, 2784-2793; Ge, Q. et al., ACS Appl. Mater. Interfaces 2015, 7, 28545-53), the AEM of XL-rPNB had higher conductivity at moderate λ (10-30), suggesting that the AEM of XL-rPNB is a promising candidate for electrochemical applications.

[0218] Thermal Stability: The thermal stability of AEM by ROMP was evaluated using thermogravimetric analysis (TGA) as shown in Figure 29A. There are three mass loss steps in the TGA. The first step is the loss below 100°C, which corresponds to the loss of water and any remaining organic solvent in the film. The second step at about 200°C is the loss of quaternary ammonium groups (N) since the weight loss is close to the QA mass of AEM. + (CH3)3, corresponds to the loss of QA (quaternary ammonium). For example, XL35-X 60 -Y 40 The weight loss of XL35-rPNB-X is about 12 wt % in the second step, with the QA group remaining at about 13 wt %. The third mass loss is most likely due to the decomposition of the polymer backbone. Therefore, the poly(norbornene) backbone prepared by ROMP is sufficiently stable at 80 °C for electrochemical devices, such as fuel cells. Furthermore, Figure 29B shows that XL35-rPNB-X 60 -Y 40 , XL20-rPNB-X 22 -Y 78 and XL20-rPNB-LY 100 Material T g The higher the number of ionic repeat units, the higher the T g Corresponds to.

[0219] Mechanical stability: Fully hydrated and dry XL-rPNB-X 60 -Y 40 , XL-rPNB-X 22 -Y 78 and XL-rPNB-LY 100 The mechanical properties of the membranes are shown in Figure 30. The elongation at break values ​​of the hydrated AEM are greater than 14.0%, but the respective tensile strengths are relatively low, <2.6 MPa. 60 -Y 40 The elongation at break (tensile stress = 2.5 MPa, strain = 51.7%) was the highest value obtained. 22 -Y 78This suggests that the higher ion content in the AEM reduces the mechanical properties. 100 (1.9 MPa, 24.5%) was higher than that of XL20-rPNB-Y due to its higher molecular weight. 100 The dry AEM had higher tensile strength (>10 MPa) than the hydrated membrane, indicating that the presence of absorbed water reduces the mechanical strength.

[0220] Alkaline stability: XL20-rPNB-LY 100 (4.51meq / g), XL20-rPNB-X 22 -Y 78 (3.78 meq / g) and XL35-rPNB-X 60 -Y 40 The alkaline stability of the (2.20 meq / g) membranes was evaluated by immersing them in 1 M NaOH at 80°C for 500 hours, as shown in Figure 31A. All tested AEMs maintained their mechanical properties, flexibility, and strength after immersion in NaOH. There was a slight increase in conductivity after 24 hours, which may be due to a more complete conversion of either bromide or carbonate ions to hydroxide ion form. Most membranes showed little or no decrease in conductivity from the initial value. XL20-rPNB-LY, which had a high IEC (4.51 meq / g), 100 However, it retained its initial conductivity value (within experimental error) after 792 hours at 80 °C in 1 M NaOH, confirming its excellent chemical stability. 60 -Y 40 ) the conductivity decreased by 1.44% after 576 hours. 22 -Y 78 The membrane showed a 4.77% reduction after 672 hours. As shown in Figure 31B, FT-IR analysis showed a peak at 1490 cm after alkaline treatment. -1 , 1260cm -1 and 1142 cm -1(Mohanty, A. D et al., Macromolecules 2015, 48, 7085-7095; Chen, D et al., ACS Appl. Mater. Interfaces 2012, 4, 5775-5781), suggesting that the AEM chemical structure remains intact and that the loss of conductivity may be caused by cracks along the AEM edges.

[0221] Fuel Cell Testing: To ensure that the membrane was robust, conductive, and stable enough to be used in a membrane electrode assembly (MEA) and electrochemical device, the AEM from ROMP was tested in an AEM fuel cell. The MEA was XL20-rPNB-LY. 100 , XL20-rPNB-X 22 -Y 78 and XL35-rPNB-X 60 -Y 40 Each of the membranes was constructed and operated at 60 °C in a H / O fuel cell as shown in Figure 32. 22 -Y 78 The open circuit voltage of the cell with the membrane was a modest 0.60 V. The poor mechanical properties of the membrane caused small cracks, leading to fuel crossover and / or cell short circuit. 100 Although the membrane was more robust, its open cell voltage was still somewhat low (0.70 V), which was most likely due to high gas crossover resulting from high water uptake. 60 -Y 40 had a lower IEC and the best mechanical properties. The open circuit voltage was 0.83 V. 100 and XL35-rPNB-X 60 -Y 40 The maximum power density of the fuel cell is 333mA / cm 2 at 126mW / cm 2 and 401mA / cm 2 at 172mW / cm 2These tests indicate that the conductivity and mechanical properties must be optimized for the intended application of the membrane. Variables to be considered include the operating temperature and transmembrane pressure. Optimization and further testing of these materials may be the subject of future reports.

[0222] In summary, a series of ROMP-crosslinked poly(norbornene)s were synthesized and evaluated for their potential use in electrochemical devices. The polymers were all composed of a hydrocarbon backbone and flexible alkyl side chains with quaternary ammonium head groups. By selecting an appropriate ratio of hydrophobic and halogenated monomers for G3, a polymer with a very high IEC (4.73 meq / g) was synthesized. Mild crosslinking (20 mol% crosslinker concentration) was used to achieve high hydroxide ion conductivities of 99 mS / cm at 25 °C and 195 mS / cm at 80 °C, higher than previously reported ROMP-based AEMs (XL20-rPNB-LY). 100 ) Furthermore, XL20-rPNB-LY 100 The membrane had excellent alkaline stability. Further optimization and enhancement of the membrane properties may lead to higher fuel cell performance.

[0223] Example 4 3.4W / cm 2 Achieving alkaline polymer fuel cells: Composite crosslinked poly(norbornene) anion-conducting membranes for high power output, durability, and water management Energy conversion devices using solid polymer electrolytes, such as fuel cells and electrolyzers, are promising options for clean energy generation and storage because they have high thermodynamic efficiency and are designed in a solid state (Steele, BC et al., Nature 2001, 414, 345). These devices are also scalable and can be used for transport, remote and distributed power generation, and large-scale facilities for electricity and hydrogen production.

[0224] Polymer electrolyte membranes for fuel cells and electrolyzers are broadly divided into two categories: proton exchange membranes (PEMs) and anion exchange membranes (AEMs), based on the predominant charge-carrying ion. While commercial fuel cell vehicles and stationary generators based on PEM membranes exist, significant costs are associated with platinum-based electrocatalysts and perfluorinated membranes. Because a high-pH environment favors the oxygen reduction reaction (ORR) kinetics in fuel cells (and water oxidation kinetics in electrolyzers) and allows the use of non-Pt catalysts, AEM-based devices have the potential for lower cost of ownership compared to PEM-based devices (McLean, GF et al., International Journal of Hydrogen Energy 2002, 27 (5), 507-526; Dekel, DR, et al., Journal of Power Sources 2018, 375, 158-169). Also, a variety of low-cost monomers can be used to synthesize hydrocarbon-based hydroxide ion-conducting polymers that are stable in alkaline conditions compared to the perfluorinated polymers required for PEM-based electrochemical devices (Varcoe, JR et al., The Journal of Physical Chemistry B 2006, 110 (42), 21041-21049; Varcoe, JR et al., Energy & Environmental Science 2014, 7 (10), 3135-3191). Perfluorinated polymers are expensive and hazardous to synthesize.

[0225] Critical metrics for AEMs include (i) high anion (e.g., hydroxide ion) conductivity, (ii) long-term alkaline stability at operating temperatures, (iii) robust mechanical properties to withstand pressure differentials during use, and (iv) control of excessive water uptake that could interfere with ion transport within the electrodes and membranes (Gottesfeld, S. et al., Journal of Power Sources 2018, 375, 170-184). There have been several reports of AEMs with hydroxide ion conductivities (at 60°C to 80°C) exceeding 100 mS / cm (Mandal, M. et al., Journal of Membrane Science 2019, 570-571, 394-402; Dang, H.-S. et al., Journal of Materials Chemistry A 2016, 4 (30), 11924-11938; Liu, L. et al., Journal of Materials Chemistry A 2018, 6 (19), 9000-9008; Liu, L. et al., Journal of Materials Chemistry A 2016, 4 (41), 16233-16244). More recent reports of AEMs show conductivities of 200 mS / cm or close to 200 mS / cm at 80°C (Mamlouk, M. et al., International Journal of Hydrogen Energy 2012, 37 (16), 11912-11920; Zhu, L.; Zimudzi, TJ et al., Polymer Chemistry 2016, 7 (14), 2464-2475). High conductivity AEMs have conductivities >1 W / cm. 2These have been combined with optimized electrodes (using either Pt or non-Pt catalysts) to obtain AEM-based fuel cells with a power output of 2 W / cm (Wang, L. et al., Chemical Communications 2017, 53 (86), 11771-11773; Omasta, TJ et al., Journal of Power Sources 2018, 375, 205-213; Omasta, TJ; Peng, X. et al., J Electrochem Soc 2018, 165 (15), J3039-J3044; Wang, L. et al., Green Chemistry 2017, 19 (3), 831-843). The current record for AEM fuel cell power is 2 W / cm. 2 (Omasta, T. et al., Energy & Environmental Science 2018, 11 (3), 551-558; Wang, L. et al., Journal of Materials Chemistry A 2018, 6 (31), 15404-15412)). AEM fuel cells are known to be sensitive to the relative humidity in the fuel and oxidant streams and to water uptake in the AEM membrane and ionomer. Proper water management in the membrane and electrodes is crucial for achieving high power density. Water is electrochemically generated at the anode during the hydrogen oxidation reaction (HOR) and consumed at the cathode by the ORR in AEM fuel cells. Water is transported from the cathode to the anode by electroosmotic drag as hydration water for the conducting anions. Water also diffuses back from the anode to the cathode. Without adequate water uptake in the membrane and electrodes, ionic conductivity is impaired and polymer degradation is accelerated due to higher effective hydroxide ion concentrations in the AEM. On the other hand, too much water can easily flood the thin catalyst layer, hindering efficient ion flow in the electrodes and membrane. Mechanical degradation of the membrane can also occur due to higher internal stress and expansion in the AEM.

[0226] Atmospheric carbon dioxide interferes with the performance of hydroxide-based AEM devices. While this issue is not directly studied herein, it is worth noting that carbonate or bicarbonate ions can be formed by the reaction of CO with hydroxide ions. The mobility of carbonate and bicarbonate ions is lower than that of hydroxide ions, reducing the conductivity of ostensibly high-conductivity AEMs (Pandey, TP et al., Physical Chemistry Chemical Physics 2015, 17 (6), 4367-4378). In contrast to PEM devices, the conductivity and peak power density for AEM fuel cells are often reported under CO2-free conditions so that they can be matched for performance comparisons. It is also clear that AEMs with very high hydroxide ion conductivity are required, as values ​​decrease when operated in the presence of carbon dioxide.

[0227] Because the number of ions cannot be increased independently, achieving high conductivity would be disadvantageous due to excessive water uptake, and therefore requires efficient ion channels (i.e., higher ion exchange capacity (IEC)) in AEMs. It has been shown that high-mobility ion channels can be formed through phase separation achieved by the use of block copolymers (BCPs) (Huang, G. et al., J Electrochem Soc 2017, 164 (14), F1648-F1653; Pan, J. et al., Energy & Environmental Science 2014, 7 (1), 354-360; Wang, J. et al., ChemSusChem 2015, 8 (24), 4229-4234). Nanochannels were created by nanophase separation between the hydrophobic and hydrophilic blocks of BCP (Park, D.-Y. et al. The Journal of Physical Chemistry C 2013, 117 (30), 15468-15477; Wang, L. et al. Soft Matter 2016, 12 (24), 5359-5371; Li, Y. et al. Macromolecules 2015, 48 (18), 6523-6533). It is important to note that not all BCP morphologies result in high conductivity, as the channels must be interconnected for efficient ion conduction (Chen, C. et al. Journal of Materials Chemistry A 2016, 4 (11), 4071-4081). The nature of the polymer backbone and the type and location of hydrophilic groups within the polymer are important for long-term AEM stability at high pH.Polar moieties within polymers or side groups, such as ether, ketone, or ester linkages, have been experimentally shown to be susceptible to nucleophilic attack and backbone degradation (Mohanty, AD et al. Macromolecules 2016, 49 (9), 3361-3372; Mohanty, AD et al. Journal of Materials Chemistry A 2014, 2 (41), 17314-17320; Arges, CG et al. ACS Applied Energy Materials 2018, 1 (7), 2991-3012). Placing a cationic head group at the end of a long pendant alkyl tether (C4-C6) has also been found to be an effective strategy for mitigating polymer degradation (Pan, J. et al., Energy & Environmental Science 2013, 6 (10), 2912-2915). Quaternary ammonium head groups, particularly the trimethylammonium cation, have been found to provide an excellent balance of conductivity and stability, although other conductive groups also offer advantages (Hibbs, MR et al., Journal of Polymer Science Part B: Polymer Physics 2013, 51 (24), 1736-1742; Liu, L. et al. Journal of Polymer Science Part A: Polymer Chemistry 2018, 56 (13), 1395-1403).

[0228] In this example, poly(norbornene) (PNB) BCP synthesized by vinyl addition polymerization is used as the AEM. PNB is synthesized from a low-cost precursor material (dicyclopentadiene) and has a high glass transition temperature (T g) PNB also has a compact monomer size and an all-hydrocarbon backbone, which allows for the creation of AEMs with very high IEC (Martinez-Arranz, S. et al. Macromolecules 2010, 43 (18), 7482-7487). This material has previously been shown to form extremely stable polymers with higher IEC values ​​approaching 4 meq / g (JA Kaitz, et al., Macromolecules. 46 (2013) 608-612). Light crosslinking was used to control water uptake and provide additional mechanical strength without encountering the problem of high crosslink density. Thin films are desirable to minimize ohmic loss in AEMs. Thin polytetrafluoroethylene (PTFE) reinforcements were used to cast the membranes and make them mechanically tough (Merle, G. et al. Journal of Membrane Science 2011, 377 (1), 1-35; Quartarone, E. et al., Materials (Basel, Switzerland) 2017, 10 (7), 687). In the past, similar techniques have been used to fabricate composite AEMs for fuel cells, achieving <350 mW / cm 2 (Zhang, F. et al. Journal of Materials Chemistry 2010, 20 (37), 8139-8146; Zhao, Y. et al. Journal of Power Sources 2013, 221, 247-251). The membrane used in this study achieved a peak power density of up to 3.4 W / cm at 80 °C using H2 / O2. 2 Conductivity, water uptake, and toughness were balanced to produce a fuel cell with a peak power density of 1000 kW, significantly higher than the highest AEM fuel cell reported to date. The membrane was also shown to be stable with a runtime of 545 hours, also the longest runtime of any AEM fuel cell reported to date.

[0229] Synthesis of Block Copolymer and Membrane Formation: The synthesis of the tetrablock PNB copolymer GT64 with 64 mol % hydrophilic monomer was carried out according to the examples previously described herein. The IEC of the polymer was determined as described in the examples herein. 1 The number average molecular weight (M) of the tetrablock copolymer was calculated based on H NMR analysis using a Bruker Avance 400 MHz NMR instrument and CDCl3 as the solvent. n ) and polydispersity index (M w / M n ) was determined by GPC (Shimadzu) equipped with an LC-20 AD HPLC pump and a refractive index detector (RID-20A, 120V). GPC measurements were performed at 30°C using eluent in THF at a flow rate of 1.0 mL / min and calibrated against polystyrene standards, as previously described herein in previous examples.

[0230] Light crosslinking was achieved by adding the crosslinker N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) to the polymer / solvent solution. The mole percentages of crosslinker relative to available headgroup sites were 2.5 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, and 25 mol%. For example, GT64-5 has 5 mol% TMHDA relative to the moles of headgroups in the BCP. The polymer solution was then solvent-cast onto a PTFE reinforcement layer by Xergy, Inc. (Harrington, DE, United States) to form a composite film. The composite membrane was immersed in a 50 wt% aqueous trimethylamine solution at room temperature for at least 48 hours to convert the bromoalkyl tethers to quaternary ammonium headgroups. The quaternized membrane was thoroughly rinsed with DI water and stored in DI water until ready for use.

[0231] Water uptake, dimensional swelling ratio, hydration number (λ): The water uptake of the membrane is calculated by the following formula 1 (where M d is the dry mass of the membrane, and M wis the mass of the fully hydrated membrane after removing the surface excess water).

[0232]

number

[0233] The swelling ratio is calculated by the following formula 2 (where V d is the dry volume of the membrane, and V w is the volume of the fully hydrated membrane after removing the excess water on the surface).

[0234]

number

[0235] Mechanical Properties: The storage modulus of the reinforced composite membranes was measured by dynamic mechanical analysis (DMA) using a TA Instruments Q800 in 1 Hz single-frequency strain mode at 30 °C in air. Fully hydrated rectangular specimens were mounted in the DMA using tension clamps after removing surface water. The DMA experimental parameters were set to 0.1% strain with 125% force follow-up and a preload force of 0.01 N.

[0236] Fabrication of membrane electrode assemblies (MEAs): Gas diffusion electrodes (GDEs) were prepared by manually spraying catalyst layers onto gas diffusion layers (GDLs, Toray TGP-H-060 with 5% or 20% PTFE dewetting) using a method similar to that described by Omasta et al. (Omasta, TJ et al. Energy & Environmental Science 2018, 11 (3), 551-558). Radiation-grafted AEI ionomers based on ETFE-[poly(ethylene-co-tetrafluoroethylene)] were provided by Varcoe and Poynton et al. (Poynton, SD et al. Journal of Materials Chemistry A 2014, 2 (14), 5124-5130). To form the cathode catalyst ink mixture (20 wt% ionomer), ETFE AEI solid ionomer was finely ground using a mortar and pestle and then mixed with Vulcan carbon-supported Pt (Alfa Aesar HiSPEC 4000). A small amount of DI water (1 ml) was then added to the solid mixture, and the mixture was ground for an additional 10 minutes to avoid particle agglomeration and then transferred to a vial. 2-Propanol was added to the mortar (total of 9 ml) to rinse any remaining powder, which was then transferred to the mixture. The mortar was rinsed with 2-propanol two to three more times to ensure that most of the ink mixture was collected. The final ground ink mixture was sonicated for 20 seconds using a sonic probe, followed by an additional 20 minutes in an ice bath, followed by 25 cm sonication. 2 The platinum and platinum-ruthenium metal loadings of these GDEs were determined by X-ray fluorescence (XRF) and are shown in Table 6. The oversized 5 cm 2 GDEs were used to fabricate the MEAs. This process was repeated using Vulcan carbon-supported PtRu catalyst and 8% PTFE (20 wt. % ionomer) for the anode catalyst ink mixture. 2To assemble using PNB composite AEM, 25cm 2 5cm from the GDE 2 Two GDEs (anode and cathode) were cut out.

[0237] MEA assembly and fuel cell testing: The anode and cathode GDEs and membranes were ion-exchanged in 1 M KOH solution for a total of 60 minutes (base solution was refreshed every 20 minutes) before assembling the cell. The membrane was sandwiched between two GDEs and compressed together, separating them by 5 cm. 2 The cell was mounted between two single-pass serpentine flow graphite plates and a PTFE gasket on Fuel Cell Technologies hardware. The total torque applied to the cell was 40 in-lb at a compression ratio of 25%.

[0238] The fuel cell was placed in a test station with the cell temperature set to 60°C or 80°C. H2 and N2 were flowed through the anode and cathode, respectively, until the desired temperature was achieved. Once the desired temperature was reached, N2 was switched to O2, and a constant voltage of 0.5 V was applied to break in the cell. After a stable exchange current density was established, the anode and cathode dew points were increased or decreased to optimize the relative humidity (RH) of the inlet gas on both sides of the cell. After the cell was equilibrated at the intended RH for both electrodes, voltage polarization curves were measured by sweeping the voltage from OCV to 0.1 V. Once all of the initial performance at various RHs was achieved, the cell was subjected to a cell durability test at 600 mA / cm2 in air without O2 or CO2. 2 The current density was held constant at 1000 kJ / s. The cell performance was monitored over time for a minimum of 24 hours.

[0239] Electrochemical properties: High frequency resistance (HFR) was analyzed by electrochemical impedance spectroscopy (EIS) using a booster with a Metrohm Autolab potentiostat / galvanostat. Area specific resistance (ASR) of the membrane was calculated using HFR. Hydrogen crossover was measured using the same instrument, with H2 and N2 flowing through the anode and cathode, respectively.

[0240] Results: The AEMs used in this study were composite films fabricated from solvent-cast high-IEC vinyl-added poly(norbornene) BCP with a thin polytetrafluoroethylene (PTFE) reinforcement layer manufactured by Xergy, Inc. The PTFE reinforcement provides mechanical strength, so thin films (<20 μm) can be used. The same base polymer was used to fabricate all composite membranes. This polymer was synthesized according to previous reports and had a molecular weight (M n The molecular weight (MW) of the polymer was 51.0 kDa with a polydispersity index (PDI) of 2.02. This range of molecular weight and polydispersity has been found to result in cast membranes with conductivity and mechanical strength. Previous reports have shown that a light degree of crosslinking is beneficial for membrane ionic conductivity, especially for high IEC materials. A high degree of crosslinking can inhibit ionic mobility and cause brittleness. The crosslinker (TMHDA) concentration of the membrane was investigated by preparing composite AEMs with 0 mol%, 2.5 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, and 25 mol% crosslinker (i.e., mol % relative to the bromine ion head groups in the polymer). The IEC of the final polymer decreased slightly with crosslinker concentration (from 3.37 meq / g to 3.28 meq / g) due to the mass of crosslinker added, but the number of cationic head groups per monomer did not change. The membrane properties are summarized in Table 6.

[0241] The mechanical properties of the membranes were affected by the degree of crosslinking, as shown in Table 6. The storage modulus and resulting stiffness of the membranes were improved by crosslinking. The uncrosslinked membrane (GT64-0) had a storage modulus of only 66.8 MPa, which is similar to that of PTFE itself. Very light crosslinking (2.5 mol%) slightly increased the modulus to 75.4 MPa. The storage modulus of the membrane with the highest crosslinker concentration (25 mol%) was 553.5 MPa, eight times higher than that of the uncrosslinked sample. The higher modulus of the crosslinked membrane provides the necessary stiffness and toughness, allowing it to be handled and used in very thin forms, thereby minimizing ohmic losses during device operation.

[0242] [Table 6] a M of precursor polymer determined by GPC n . b M of precursor polymer determined by GPC w / M n . c IEC calculated after adding the molecular weight of TMHDA. d Area specific resistivity measured by EIS at 60 °C. e Storage modulus determined by DMA.

[0243] The water uptake and swelling ratio of the composite films decreased with crosslinker concentration, as shown in Table 6. The water uptake was relatively high (88%) for the uncrosslinked membrane, with a swelling ratio of 68%. Even a very low crosslinker concentration (2.5 mol%) significantly reduced the swelling ratio due to a more densely bonded structure within the crosslinked polymer network. At higher crosslinker concentrations of ≥10%, both the water uptake and swelling ratio were well below 50%, which is advantageous for reducing physical deformation when integrated into a membrane electrode assembly. The water uptake values ​​of the composite films have been found to be lower than those of free-standing films without PTFE support, as previously reported. For example, 10 mol% crosslinker resulted in a water uptake of 53% for the unreinforced polymer and only 35% for GT64-10. At 20 mol% crosslinking, the effect was even more dramatic: the water uptake was 51% for the unreinforced polymer, compared with 24% for the reinforced polymer. This indicates that the hydrophobic PTFE reinforcement contributes to the limited water uptake in these membranes.

[0244] The high frequency resistance (HFR) and area specific resistance (ASR) were evaluated using electrochemical impedance spectroscopy (EIS). A Nyquist plot obtained from EIS measurements of the MEA at 60°C is shown in Figure 33. The high frequency intercept (HFR) of the plot represents the total series ohmic resistance of the membrane, as well as any other series resistance, such as contact resistance and hardware resistance. The membrane thickness used here helps reduce the overall HFR, thereby maximizing fuel cell power output.

[0245] The ASR was calculated using the HFR of the MEA as measured by EIS. This value represents the in-plane area resistance of the membrane, which is especially important for composite membranes since the support material does not contribute to ionic conductivity. The in-plane hydroxide ion mobility depends on the orientation of the reinforcement layer and the pores of the packed membrane. The ASR values ​​of the membranes in this study are listed in Table 6. All of the membranes except GT64-2.5 had an ASR of ≤ 0.04 Ω-cm. 2 The ASR of 1.0% was 0.01, which exceeds the fuel cell integration guidelines set by the ARPA-E IONICS (U.S. Department of Energy) program. Table 6 also shows how mild cross-linking of these polymers significantly reduced water uptake. The swelling ratio was reduced to only 7%, and high conductivity was achieved without excessive water, as indicated by the reduced WU / ASR values. Achieving high conductivity by increasing WU has been shown to result in reduced mechanical stability of the membranes and devices fabricated from them.

[0246] Two sets of fuel cells were constructed using the reinforced membranes in Table 6. The fuel cells were operated with humidified H2 and O2 and 5% dewetting Toray-H-60GDL at a cell temperature of 60°C, as summarized in Table 7. After a short break-in period during which the anode and cathode RH were optimized, forward and reverse polarization scans were performed on each cell to determine the peak power density. The optimized anode and cathode dew points are listed in Table 7 using the notation (A / C), where the value of A represents the anode dew point (in degrees Celsius) and the value of C represents the cathode dew point (in degrees Celsius). This notation is used throughout this specification. Performance based on crosslinker concentration is shown in Figure 34. The cell voltage at peak power at 60°C for all samples was approximately 0.55 V. The specific power and specific current were calculated based on the peak power density, the current generated at peak power, and the metal loading of the electrodes.

[0247] In Table 7, three distinct power tiers of current density can be seen, with peak power increasing with crosslinker concentration. Among the membranes tested, the cells with the lowest performance contained membranes with 0 mol% and 2.5 mol% crosslinker concentrations, which were only 1241-1386 mW / cm, respectively. 2 The films with 5 mol% and 10 mol% crosslinker concentrations had a peak power of 1894 mW / cm, respectively. 2 and 1902 mW / cm 2 For the cell containing the GT64-15 membrane, the highest power density was observed, 2200 mW / cm at both the anode and cathode dew points at 40 °C (47.54% RH). 2 This cell achieved a peak power density of 2.02 W / cm at 60 °C, exceeding the 2.02 W / cm at 80 °C reported by Wang et al. 2 This surpasses the previous highest power output AEM fuel cell (Wang, L. et al., Journal of Materials Chemistry A 2018, 6 (31), 15404-15412).

[0248] [Table 7] a Beginning of life crossover measured by EIS. b High frequency resistance measured by EIS. c Metal loading for specific power and current determined by XRF. All other values ​​measured or calculated are based on test station data. XL = bridge. A / C = anode (A) and cathode (C) dew points (in degrees Celsius), respectively. CD (current density) = current density. PPD (peak power density) = peak power density.

[0249] As summarized in Table 8, fuel cell performance at 80°C was significantly increased. Samples with higher crosslinker concentrations were selected for testing at 80°C because of their performance at lower temperatures. The GDE used in these tests was further optimized (20% dewetting Toray-H-60), and additional care was taken to optimize the relative humidity of the anode and cathode feeds. As shown in Figure 35, there was little power density separation among the four cells tested. All cells achieved a peak power of approximately 0.53 V. Both the GT64-10 and GT64-20 achieved a peak power of approximately 3 W / cm. 2 The GT64-25 achieved a peak power output of 3.265 W / cm and had similar anode and cathode dew points. 2 , which may be due to tighter control of the physical deformation due to water swelling, but its hydroxide ion conductivity was lower than the other membranes. GT64-15 again performed best among all the membranes tested, with a peak power density of 3.368 W / cm, similar to the results obtained at 60 °C. 2 The individual polarization curves for GT64-15 are shown in Figure 36. To the inventors' knowledge, this is the highest performance reported for an AEM fuel cell, surpassing the highest previously reported value by 70%. The resulting power densities were found to be relatively similar over a relatively wide range of crosslinker concentrations. This is likely the result of the countervailing trends of mechanical stability (better at higher crosslinker concentrations) and lower conductivity, both caused by the lower WU.

[0250] [Table 8] a Early life crossover measured by EIS. All other values ​​measured or calculated are based on test station data. XL = bridge. A / C = anode (A) and cathode (C) dew points (in degrees Celsius), respectively. CD = current density. PPD = peak power density.

[0251] Previous ex-situ testing of reinforced membranes with similar IECs showed that the highest hydroxide ion conductivity occurred at a crosslinker concentration of 5 mol%. This contrasts with the results of this study, where a 15 mol% crosslinker concentration yielded the highest power density at both 60 and 80 °C. In Table 6, water uptake is normalized by ASR (WU / ASR), and IEC is normalized by ASR (IEC / ASR). These quantities provide some insight into why certain crosslinker concentrations perform better than others. IEC / ASR is similar to the conductivity per IEC (σ / IEC), which has previously been used to measure how efficiently conducting groups transport hydroxide ions. For the membranes in this study, the ion conduction efficiencies were all very similar, ranging from only 3.20 to 3.33. This is due to the minimal variation in ASR and IEC among the samples tested. An additional parameter to investigate was WU / ASR, which showed that although hydroxide ion conductivity decreased with crosslinker concentration, minimum WU (and resulting expansion) provided significant benefits so that cell performance was not significantly compromised.

[0252] One drawback of using thin composite membranes is higher hydrogen crossover, especially at low temperatures. Prior to the break-in procedure, hydrogen crossover tests were performed by applying H2 to the anode and N2 to the cathode. The cathode current measured at a cell voltage of 0.5 V corresponds to the hydrogen crossover from the cathode to the anode. The hydrogen crossover values ​​are listed in Tables 6 and 7. Crossover does not appear to be a function of membrane thickness or crosslinker concentration, with a maximum of 54 mA / cm2 for GT64-10. 2 The crossover was as high as 1.1 V. It is suspected that crossover occurred primarily at unforeseen weak or thin spots in the membrane, but no obvious areas were identified. The enhanced crossover effect of GT64-10 can be seen in the lower open circuit voltage (OCV) values. The OCV ranged from 0.881 V to 0.950 V. Other fuel cells using the same electrode formulation had OCV values ​​of approximately 1.1 V.

[0253] The relative humidity at the anode and cathode inlets is known to play a crucial role in the performance of alkaline exchange membrane fuel cells. Water uptake in the hydrogen and oxygen inlet streams must be carefully balanced with water production at the anode, water diffusion through the membrane, and water consumption at the cathode. Factors such as catalyst activity and loading can affect each individual electrode differently, thereby affecting overall cell performance. As previously mentioned, three tiers of power output can be seen in Figure 34 versus the amount of crosslinker in each membrane. However, additional trends can be seen in this data. Not only does performance actually increase with crosslinker concentration, but the amount of humidity required also decreases. As previously reported, water uptake decreases with increasing crosslinker concentration in the polymer network. (JM Schwartz, et al., J. Polym. Sci. Part A Polym. Chem. 56 (2018) 221-228) As can be seen from the water uptake data in Table 6, higher crosslinker concentration reduces WU. However, a denser and more rigid polymer network may also trap water within the film, limiting the rate of dryout, which was particularly problematic for the thin films in this study and may indicate that a critical crosslinker concentration is required to maintain proper hydration.

[0254] Cells with a crosslinker concentration of ≥10% operated at 60°C had peak power densities at 40°C or 47.5% RH anode and cathode dew points. Figure 37 shows the RH optimization for the GT64-15 membrane. At 50 / 50 anode and cathode dew points, there is clearly too much water in the system, flooding the electrodes and reducing power output. Performance steadily increases as humidity is reduced to 40 / 40.

[0255] This trend continued at a moderate amount of crosslinker (5 mol%), where the required RH was 64.5% RH and 74.8% for the anode and cathode, respectively. At crosslinker concentrations ≦2.5 mol%, the anode and cathode RH needed to be 69.5% RH to achieve the highest peak power. RH optimization for GT64-2.5 is shown in Figure 37. At 100% RH, lower power was observed due to cell flooding. At the opposite end of the spectrum (50 / 50 dew point), the membrane became too dry and low power was also observed. At a 55 / 55 dew point, significantly higher power could be achieved due to the optimal balance of inlet and product water.

[0256] Figure 38 shows the RH optimization behavior of a membrane without any crosslinker. While the separation of the data is not clear, the optimal dew point for this cell is between 50 / 50 and 55 / 55. When the dew point was set to 45 / 45, lower power output was observed due to lack of hydration.

[0257] The long-term stability of the cells tested here was studied using a 5% anti-wetting GDL. The durability of GT64-15 was tested at 80°C using CO2-free air. Before switching to CO2-free air, the cell achieved a power dissipation of 2.3 W / cm2 at 80°C in H2 / O2, as shown in Figure 40. 2 Figure 41 shows that a constant current density of 600 mA / cm 2Figure 1 shows hourly data on cell voltage at 1000 kJ / s over time. Overall, the cell operated for 545 hours without detectable membrane degradation. To the inventors' knowledge, 545 hours is also the longest durability test of an AEM fuel cell to date. During the first 300 hours, cell performance was observed to decline by approximately 17% over this time. However, the origin of the degradation can be attributed to the radiation-grafted ETFE AEI ionomer in the electrode, which was reported to have degraded by approximately 6.2% after 500 hours. This change in performance likely resulted from a change in water dynamics in the electrode over time. Therefore, the humidity was adjusted to 78 / 78 after 300 hours, restoring the initial level of performance. After the next 150 hours, the anode and cathode dew points were increased to 79 / 79 for the final 95 hours of the durability test. After adjusting for water uptake, the cell voltage and HFR also returned to their initial values, indicating that an appropriate hydration level had been achieved. Indeed, the initial HFR (0.043 Ω-cm) 2 ) and final HFR (0.042 Ω-cm 2 ) shows that the performance was unchanged, indicating that a longer break-in period is required for the AEM membrane and electrodes.

[0258] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, changes, or improvements thereon may be made by those skilled in the art, and are intended to be encompassed by the following claims.

Claims

1. A multi-block copolymer, (a) one or more norbornene-based hydrophilic blocks comprising hydrophilic monomers having a norbornene structure substituted with a branched or unbranched, saturated C2-C20 alkyl chain having a cationic head group; and (b) one or more norbornene-based hydrophobic blocks, the norbornene-based hydrophobic block comprising a hydrophobic monomer having a norbornene structure substituted with a branched or unbranched saturated C1-C20 alkyl chain, the alkyl chain being optionally halogenated; The multi-block copolymer comprising:

2. The one or more norbornene-based hydrophobic blocks comprise hydrophobic monomers having a norbornene structure substituted with a branched or unbranched saturated C1-C20 alkyl chain, and have a structure represented by formula (I): 【Chemistry 1】 where: R １ is a branched or unbranched saturated C1-C20 alkyl chain or halogenated alkyl chain; n is an integer from 1 to about 1,000; The multi-block copolymer of claim 1 .

3. R １ The multi-block copolymer of claim 2, wherein is a C4 to C10 alkyl chain.

4. The one or more norbornene-based hydrophilic blocks (a) comprise one or more hydrophilic monomers having a structure represented by formula (III): 【Transformation 3】 where: R ４ is a branched or unbranched saturated C2-C20 alkyl chain substituted with one or more cationic head groups; m is an integer from about 10 to about 1,000; The multi-block copolymer according to any one of claims 1 to 3.

5. R ４ 5. The multi-block copolymer of claim 4, wherein is a branched or unbranched, saturated C3 or C4 alkyl chain substituted with one or more cationic head groups.

6. 6. The multi-block copolymer of claim 4 or 5, wherein the one or more cationic head groups comprise a quaternary ammonium head group.

7. 7. The multi-block copolymer of claim 6, wherein the cationic head group is a terminal quaternary ammonium head group.

8. The multi-block copolymer of any one of claims 1 to 7, wherein the copolymer comprises from 2 to 8 blocks.

9. The multi-block copolymer of claim 8 , wherein the copolymer comprises four blocks.

10. The multi-block copolymer according to any one of claims 1 to 9, (i) the mole percentage of the one or more norbornene-based hydrophobic blocks (b) is from about 30% to about 40%; and / or (ii) the mole percentage of the one or more norbornene-based hydrophilic blocks (a) is from about 60% to about 70%; and / or (iii) the mole percentage of the one or more norbornene-based hydrophobic blocks (b) is from about 10% to about 30%; and / or (iv) the mole percent of the one or more norbornene-based hydrophilic blocks (a) is from about 70% to about 90%; The multi-block copolymer.

11. An anion exchange membrane (AEM) comprising the multi-block copolymer of any one of claims 1 to 10.

12. 12. The AEM of claim 11, wherein the one or more norbornene-based hydrophilic blocks are crosslinked with a crosslinking agent.

13. 13. The AEM of claim 12, wherein the crosslinker is a branched or unbranched saturated C2-C10 alkyl chain, or a saturated C6 alkyl chain.

14. 14. The AEM of claim 12 or 13, wherein the crosslinker is an alkyldiamine comprising a branched or unbranched, saturated C2-C10 alkyl chain, or a multiamine alkyl comprising a branched or unbranched, saturated C2-C10 alkyl chain having at least two amine functional groups.

15. 15. The AEM of any one of claims 12 to 14, wherein one or more cationic head groups of the one or more norbornene-based hydrophilic blocks in the multi-block copolymer are crosslinked to each other via the crosslinking agent.

16. The AEM of any one of claims 12 to 15, wherein the concentration of the cross-linking agent is about 5 mol% to 50 mol%.

17. 17. The AEM of any one of claims 12 to 16, wherein the multi-block copolymer comprises a crosslinker having one or more branched or unbranched saturated C2-C20 alkyl chains attached to one or more cationic head groups of one or more norbornene-based hydrophilic monomers.

18. The AEM of any one of claims 12 to 17, comprising a structure represented by the following formula: 【Chemistry 4】 where: R ４ is a branched or unbranched saturated C1-C20 alkyl chain; R １ is a branched or unbranched saturated C2-C20 alkyl chain; X is a cationic head group containing a cationic charged heteroatom; R ５ is a crosslinker comprising a branched or unbranched saturated C2-C10 alkyl chain; Each R ５ are independently present or absent, and at least one of the cationic norbornene-based monomers in said AEM is R ５ is crosslinked by a group, n, m, o, and p are integers independently selected from about 10 to about 1,000.

19. The AEM of any one of claims 12 to 18, further comprising a stabilizer.

20. 20. The AEM of claim 19, wherein the stabilizer is perfluorinated tetrafluoroethylene (PFTE) or polyolefin (PO).

21. 21. The AEM of any one of claims 12 to 20, comprising one or more anion-conducting channels.

22. (a) having a tensile strength of about 10 to about 500 MPa; (b) having an elongation at break percentage of about 10 to about 200; (c) having a Young's modulus of about 0.005 to about 1 GPa; (d) having an ion exchange capacity of about 1.5 to about 4.5 meq. / g; (e) having a hydroxide ion conductivity of about 35 to about 250 mS / cm at 80°C; (f) having a water uptake percentage of about 10% to about 70%; and / or (g) having a hydration number λ of about 6 to about 30.

23. A method for making the multi-block copolymer of any one of claims 1 to 10, comprising vinyl addition polymerization.

24. 10. A method for making the multi-block copolymer of claim 1 comprising ring-opening metathesis polymerization (ROMP).

25. 11. A method for producing a crosslinked multi-block copolymer, comprising crosslinking one or more norbornene-based hydrophilic blocks in the multi-block copolymer of any one of claims 1 to 10 with one or more crosslinking agents.

26. 26. The method of claim 25, wherein the crosslinker is a multiamine alkyl chain comprising a branched or unbranched saturated C2-C10 alkyl chain having at least two amine functional groups.

27. 27. The method of claim 25 or 26, wherein the cross-linking agent is an alkyldiamine containing a branched or unbranched, saturated C2 to C10 alkyl chain.

28. A device comprising a multiblock copolymer according to any one of claims 1 to 10 and / or an anion exchange membrane (AEM) according to any one of claims 11 to 22.

29. 30. The device of claim 28 which is an electrochemical device.

30. 30. The device of claim 29, wherein the electrochemical device is selected from a fuel cell, an electrolyzer, and a redox flow battery.

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