Functionalized polybenzimidazole polymers for ionomer and proton exchange membrane applications

Abstract

The present invention relates to ion exchange functionalized polymer molecules comprising repeating units having a benzimidazole unit as a backbone, a side chain, or at least a portion of both. The ion exchange functionalized polymer molecule further includes an ion exchange group attached to the repeating unit. The ion exchange group may be a tetravalent boron group or a metal fluoride, and the metal fluoride may be a multivalent metal atom.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 302,755, filed on January 25, 2022, which is hereby incorporated by reference in its entirety. Background Art

[0003] In electrochemical cells such as hydrogen fuel cells and water electrolysis systems, proton exchange membranes (PEMs) are used to selectively transport protons. + ) while being impermeable to gases. PEMs are usually composed of a porous framework with highly acidic functional groups. For example, PEMs based on polyfluorosulfonic acid contain a porous framework of poly(tetrafluoroethylene) (PTFE) with sulfonic acid groups. The easily dissociated sulfonic acid groups act as proton transporters in the membrane. In hydrogen fuel cells, hydrogen (H2) is separated into protons (H + ) and electrons. The protons pass through the PEM and combine with oxygen (O2) at the cathode to produce water, while the electrons flow through an external circuit to generate electricity. In a water electrolysis system, electricity decomposes water at the anode into oxygen (O2) and protons (H + The protons pass through the PEM and combine with electrons at the cathode to produce hydrogen (H2).

[0004] A membrane electrode assembly (MEA) may include a PEM between a first catalyst layer and a second catalyst layer. The catalyst layer is a conductive electrode (anode and cathode) having an embedded electrochemical catalyst such as a metal, a metal alloy or a metal oxide. The catalyst may be bonded to a catalyst solid support, which is typically a conductive high surface area carbon (e.g., graphite or graphene). The electrochemical catalyst reduces the activation energy required for an electrochemical reaction at the electrode, such as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in water electrolysis applications and hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in fuel cell applications.

[0005] In some applications, the catalyst layer includes a supported catalyst mixed with an ionomer, an ion-conducting polymer. The ionomer binds the catalyst within the electrode, binds the catalyst layer on the PEM, and provides a pathway for cations (e.g., protons), thereby improving cation conductivity. In some MEAs, the catalyst layer is formed separately from the PEM and is layered on the PEM in the MEA stack. In other MEAs, the catalyst layer is coated on the PEM to form a catalyst-coated membrane (CCM).

[0006] PEM and ionomers and the molecular functional groups responsible for proton transport properties in them should remain robust under harsh reaction conditions of redox stress. In water electrolysis and fuel cell applications, conventional polymers used in PEM and conventional polymers used as ionomers mainly contain sulfonic acid functional groups as proton transport agents. The easily dissociated sulfonic acid groups serve as proton transport agents in the PEM. However, water electrolysis and fuel cell applications involve strong redox chemistry under ambient temperature to high temperature and acidic conditions. Sulfonic acid functional groups have only limited ability to withstand redox stress from electrochemical operations, which is mainly due to the inherent physicochemical properties of sulfur. Summary of the invention

[0007] The following description presents a simplified overview of one or more aspects of the devices, compositions and / or methods described herein in order to provide a basic understanding of these aspects. The summary of the invention is not an extensive review of all expected aspects, and is neither intended to identify the key or important elements of all aspects, nor to describe the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects of the devices, compositions and / or methods described herein in a simplified form as a prelude to the more detailed description presented below.

[0008] In some exemplary examples, the ion exchange functionalized polymer molecule comprises: a repeating unit comprising a benzimidazole group as at least a part of the main chain, the side chain, or both; and an ion exchange group attached to the repeating unit, wherein the ion exchange group comprises a tetravalent boron group or a metal fluoride comprising a multivalent metal atom.

[0009] In some exemplary embodiments, the method of preparing an ion exchange functionalized polymer molecule includes attaching an ion exchanger to a repeating unit of a polymer molecule, wherein the polymer molecule includes a benzimidazole unit as at least a portion of a main chain or a side chain of the polymer molecule, and the ion exchanger includes a trivalent boron compound or a metal fluoride, the metal fluoride including a polyvalent metal atom.

[0010] In some exemplary examples, the polybenzimidazole (PBI) polymer comprises: a main chain comprising benzimidazole units; and ion exchange groups connected to the benzimidazole units; wherein the ion exchange groups include tetravalent boron groups or metal fluoride groups, each metal fluoride group comprising a polyvalent metal atom.

[0011] In some exemplary examples, a polymer composition includes a first polymer cross-linked with a second polymer via a tetravalent boron cross-linking group, the first polymer including a first polybenzimidazole (PBI) polymer.

[0012] In some exemplary instances, a method of cross-linking a first polymer and a second polymer with a tetravalent boron cross-linking group comprises: reacting the first polymer, the second polymer, and a cross-linking agent, wherein the first polymer comprises a first polybenzimidazole (PBI) polymer, the first polybenzimidazole (PBI) polymer comprising a benzimidazole unit as at least a portion of the main chain; and the cross-linking agent comprises boric acid, an organic boronic acid, or a derivative of an organic boronic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to better understand the concepts described herein, various embodiments will be described by way of example only with reference to the accompanying drawings. The accompanying drawings illustrate various embodiments and are a part of this specification. The embodiments shown are examples only and do not limit the scope of the present disclosure. In all drawings, the same or similar reference numerals represent the same or similar elements.

[0014] Figures 1 to 4B Various exemplary reaction schemes for the synthesis of ion exchange functionalized PBI polymer molecules are shown.

[0015] Figure 5 An exemplary reaction scheme for cross-linking two PBI polymer molecules using boronic acid as a cross-linking agent is shown.

[0016] Figure 6 An exemplary reaction scheme for cross-linking PBI polymer molecules with hydroxyl-functionalized PTFE polymer using boric acid as a cross-linking agent is shown.

[0017] Figure 7 An exemplary reaction scheme for cross-linking PBI polymer molecules with hydroxyl-functionalized PTFE polymer molecules using an aminoorganoboronic acid as a cross-linking agent is shown.

[0018] Figure 8 An exemplary reaction scheme for cross-linking PBI polymer molecules with PPA polymer molecules using boronic acid as a cross-linking agent is shown.

[0019] Fig. 9 An exemplary proton exchange membrane water electrolysis system with an ion exchange functionalized PBI polymer is shown.

[0020] Fig.10 An exemplary proton exchange membrane fuel cell having an ion exchange functionalized PBI polymer is shown. DETAILED DESCRIPTION

[0021] Ion exchange functionalized polybenzimidazole (PBI) polymers, methods for preparing ion exchange functionalized PBI polymers, and methods and devices for using ion exchange functionalized PBI polymers are described herein. As described herein, ion exchange functionalized polymer molecules include repeating units and ion exchange groups. The repeating unit includes a benzimidazole unit as at least a portion of a main chain, a side chain, or both. The ion exchange group is connected to the repeating unit. The ion exchange group can be, for example, a tetravalent boron group or a metal fluoride group with a polyvalent metal atom. In some instances, the ion exchange group is directly connected to the secondary amine of the benzimidazole unit, for example, by a covalent bond between the boron atom or metal atom of the ion exchange group and the nitrogen atom of the secondary amine. In other instances, the ion exchange group is indirectly connected to the secondary amine by a linker. In other instances, the ion exchange group is indirectly connected to the phenyl unit of the repeating unit by a linker. The boron atom of the tetravalent boron group or the multivalent atom of the metal fluoride group has an extended valence and is therefore ionic and acidic in nature and can act as an ion (e.g., proton) transport agent. Therefore, the ion exchange functionalized PBI polymer can be used in ionomer applications and PEM applications.

[0022] Also described herein is the use of a tetravalent boron crosslinking group to crosslink a PBI polymer to another polymer, such as another PBI polymer, a functionalized poly(tetrafluoroethylene) (PTFE) molecule, or a poly(phosphoric acid) (PPA) polymer. In the tetravalent boron crosslinking group, the boron atom has a negative formal charge and is therefore ionic and acidic in nature and can act as an ion (e.g., proton) transport agent. Thus, crosslinked polymers having tetravalent boron crosslinking groups can be used in ionomer applications and PEM applications.

[0023] Various definitions will now be provided to aid in understanding the various aspects of the present disclosure. Each term or expression as used herein, such as alkyl, m, n, etc., when used more than once, is intended to be independent of its definition elsewhere in the present disclosure. In the event of a conflict with any patent application or patent incorporated herein by reference, the present specification including the definitions shall prevail.

[0024] As used herein, "polymer" refers to a substance containing polymer molecules of the same or different polymer species, including mixtures of polymer molecules of the same polymer species, which may differ from other polymer molecules within the same sample in terms of chain length and / or specific structural arrangement (e.g., irregularities in the orientation of monomer units, end groups, and / or irregularities in the position and / or length of any side chains or side groups). "Polymer" includes homopolymers, copolymers, terpolymers, interpolymers, etc.

[0025] As used herein, "polymer molecule" or "macromolecule" refers to a molecule of high relative molecular mass whose structure comprises a relatively large number of repetitions of units (e.g., about 100 or more monomeric units) that are actually or conceptually derived from molecules of low relative molecular mass (e.g., monomeric molecules).

[0026] As used herein, "polymerization" refers to the process of converting a monomer or mixture of monomers into a polymer.

[0027] As used herein, "oligomer" refers to a substance composed of oligomeric molecules.

[0028] As used herein, "oligomeric molecule" refers to a molecule of medium relative molecular mass whose structure comprises a relatively small repetition of units (e.g., about 10 to about 100 monomer units) that are actually or conceptually derived from molecules of lower relative molecular mass (e.g., monomer molecules).

[0029] As used herein, "oligomerization" refers to the process of converting a monomer or a mixture of monomers into oligomers.

[0030] As used herein, "ionomer" refers to a polymer composed of ionomer molecules.

[0031] As used herein, "ionomer molecule" refers to a polymer molecule in which a small but relatively significant proportion of structural units have ionizable side groups or ionic side groups (including ion exchange groups described herein) or both. Typically, no more than about 15 mole % of the structural units have ionizable side groups or ionic side groups.

[0032] As used herein, "monomer" refers to a substance composed of monomer molecules.

[0033] As used herein, "monomer molecule" refers to a molecule that can undergo polymerization or oligomerization to form a polymer molecule or an oligomer molecule. A monomer molecule contributes a structural unit to the basic structure of a polymer molecule or an oligomer molecule.

[0034] As used herein, "copolymer" refers to a polymer derived from more than one monomer.

[0035] As used herein, "structural unit" refers to an atom or group of atoms (with pendant atoms or groups, if any) comprising part of the structure of a polymer molecule (or oligomer molecule, block or chain).

[0036] As used herein, "repeating unit" refers to a structural unit, the repetition of which constitutes a polymer molecule (or an oligomer molecule, block or chain).

[0037] As used herein, "monomer unit" refers to the largest structural unit contributed by a single monomer molecule to the structure of a polymer molecule or an oligomer molecule.

[0038] As used herein, "block" refers to a portion of a polymer molecule (or oligomer molecule) that contains a number of structural units and has at least one feature that is not present in adjacent portions.

[0039] As used herein, "chain" refers to all or part of a polymer molecule (or oligomer molecule or block) comprising a linear or branched sequence of structural units between two boundary structural units, each of which may be an end group, a branch point, or other designated feature of the polymer molecule.

[0040] As used herein, "main chain" or "backbone" refers to the chain of a polymer molecule to which all other chains (long or short or both) may be considered pendants (eg, side chains).

[0041] As used herein, "side chain" refers to an oligomeric (short chain) or polymeric (long chain) branch from the backbone of a polymer molecule.

[0042] As used herein, "side group" or "pendant group" refers to a branch from a chain (eg, from the backbone) that is neither oligomeric nor polymeric.

[0043] As used herein, "crosslink" refers to a small region in a polymer molecule from which at least four chains emanate. Crosslinks are typically formed by reactions involving sites or groups on existing polymer molecules or by interactions between existing polymer molecules.

[0044] The term "cross-linked" refers to a state in which polymer molecules that were previously separate polymer molecules are linked to each other at points other than their termini, typically by covalent bonds.

[0045] As used herein, "aliphatic" compounds are hydrocarbons that are saturated or unsaturated, acyclic or cyclic, unbranched or branched, unsubstituted or substituted with one or more substituents or functional groups. As will be appreciated by those of ordinary skill in the art, "aliphatic" is intended to include, but is not limited to, alkyl, alkenyl, and alkynyl moieties in this article. Exemplary aliphatic groups include, but are not limited to, for example, methyl, ethyl, n-propyl, isopropyl, allyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, tert-pentyl, n-hexyl, and sec-hexyl moieties.

[0046] The term "alkyl" as used herein has its ordinary meaning in the art and may include saturated aliphatic groups, including straight chain alkyl, branched chain alkyl, cycloalkyl (alicyclic), cycloalkyl substituted by alkyl, and alkyl substituted by cycloalkyl. Similar conventions apply to other general terms, such as "alkenyl", "alkynyl", etc. In addition, the terms "alkyl", "alkenyl", "alkynyl", etc. as used herein encompass both substituted and unsubstituted groups.

[0047] In some embodiments, the straight or branched alkyl chain may have 1 to 30 carbon atoms in its skeleton, and in some cases may have 1 to 20 or less. In some embodiments, the straight or branched alkyl chain has 1 to 10 carbon atoms (e.g., C1-C10 for straight chain, C3-C10 for branched chain) in its skeleton, has 6 or less carbon atoms, or has 4 or less carbon atoms. Cycloalkyl may have 3 to 10 carbon atoms in their ring structure, or in some cases, may have 3 to 5, 6 or 7 carbon atoms in the ring structure. Examples of non-cyclic alkyl include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, normal-butyl, tert-butyl, normal-pentyl, neopentyl, normal-hexyl, normal-heptyl, normal-octyl, normal-decyl, normal-undecyl and dodecyl. Examples of cyclic alkyl include, but are not limited to, cyclopropyl, cyclobutyl and cyclohexyl.

[0048] The terms "alkenyl" and "alkynyl" refer to unsaturated aliphatic groups similar in length and possible substitution to the above alkyl groups, but containing at least one double bond or triple bond, respectively. Alkenyl groups include, but are not limited to, for example, vinyl, propenyl, butenyl, 1-methyl-2-butene-1-yl, etc. Non-limiting examples of alkynyl groups include ethynyl, 2-propynyl (propargyl), 1-propynyl, etc.

[0049] The term "heteroalkyl" refers to an alkyl group in which one or more hydrogen atoms or one or more carbon atoms bonded to any carbon of the alkyl group are replaced by a heteroatom. A heteroatom is any atom other than carbon. In some instances, a heteroatom is an atom selected from N, O, P, B, S, Si, Sb, Al, Sn, As, Se, and Ge. Examples of heteroalkyl groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, methylthio, ethylthio, propylthio, isopropylthio, n-butylthio, methoxymethyl, and cyano.

[0050] The terms "heteroalkenyl" and "heteroalkynyl" refer to unsaturated aliphatic groups analogous in length and possible substitution to the heteroalkyls described above, but that contain at least one double or triple bond, respectively.

[0051] The term "aryl" refers to an aromatic carbocyclic group, which is unsubstituted or substituted, having a monocyclic (e.g., phenyl), polycyclic (e.g., biphenyl) or multiple fused rings, wherein at least one ring is aromatic (e.g., 1,2,3,4-tetrahydronaphthyl, naphthyl, anthracenyl or phenanthrenyl). That is, at least one ring may have a conjugated Pi electron system, while the other adjacent (adjoining) rings may be cycloalkyl, cycloalkenyl, cycloalkynyl, aryl and / or heterocyclic groups. "Carbocyclic aryl" refers to an aryl group in which the ring atoms on the aromatic ring are carbon atoms. Carbocyclic aryl groups include monocyclic carbocyclic aryl groups and polycyclic or fused compounds (e.g., two or more adjacent (adjacent) ring atoms are common to two adjacent rings), such as naphthyl. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, tetrahydronaphthyl, indanyl and indenyl.

[0052] The term "heteroaryl" refers to an aryl group, such as a heterocycle, comprising at least one heteroatom as a ring atom. Non-limiting examples of heteroaryl include, but are not limited to, pyridyl, pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl, isoxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl, quinolinyl, and isoquinolinyl.

[0053] As used herein, the term "alkoxyl" or "alkoxy" refers to an alkyl group having an oxy group attached to the alkyl group and has the general formula RO. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, and tert-butoxy.

[0054] The term "aryloxy" refers to an aryl group having an oxy group attached to the aryl group. Examples of aryloxy groups include, but are not limited to, phenoxy groups.

[0055] Any of the above groups may be optionally substituted. Examples of substituents include, but are not limited to, aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxy, alkoxy, amino, nitro, sulfhydryl, imino, amino, phosphonate, phosphinate, carbonyl, carboxyl, alkoxycarbonyl, silyl, ether, alkylthio, heteroalkylthio, heteroarylthio, sulfonyl, sulfonamido, keto, aldehyde, ester, heterocyclic, aromatic or heteroaromatic moieties, -CF3, -CN, aryl, aryloxy, perhaloalkoxy, aralkyloxy, heteroaryl, heteroaryloxy, heteroarylalkyl , heteroarylalkyloxy, azido, amino, halide, alkylthio, oxo, acylalkyl, carboxy ester, -acylamino, acyloxy, aminoalkyl, alkylaminoaryl, alkylaryl, alkylaminoalkyl, alkoxyaryl, arylamino, aralkylamino, alkylsulfonyl, -acylaminoalkylaryl, -acylaminoaryl, hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxy-, aminoacylaminoalkyl-, cyano, alkoxyalkyl, perhaloalkyl, arylalkyloxyalkyl, (e.g. SO4(R′)2), phosphate (e.g. PO4(R′)3), silane (e.g. Si(R′)4), urethane (e.g. R′O(CO)NH R In addition, the substituent may be selected from F, Cl, Br, I, -OH, -NO2, -CN, -NCO, -CF3, -CH2CF3, -CHCl2, -CH2ORx, -CH2CH2ORx, -CH2N(Rx)2, -CH2SO2CH3, -C(O)Rx, -O2(Rx), -CON(Rx)2, -OC(O)Rx, -C(O)OC(O)Rx, -OCO2Rx, -OCON(Rx)2, -N(Rx)2, -S(O)2Rx, -OCO2Rx, -NRx(CO)Rx, -NR x (CO)N(R x )2, where each occurrence of R x Independently include, but are not limited to, hydrogen, aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, aryl, heteroaryl, alkylaryl, or alkylheteroaryl, wherein any aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, alkylaryl, or alkylheteroaryl substituents described above and herein may be substituted or unsubstituted, branched or unbranched, cyclic or acyclic, and wherein any aryl or heteroaryl substituents described above and herein may be substituted or unsubstituted.

[0056] Polybenzimidazole (PBI) polymers are a class of polymers consisting of PBI polymer molecules. PBI polymer molecules have repeating units that contain benzimidazole units as at least a portion of the backbone. The benzimidazole units include benzimidazole groups or their derivatives. Benzimidazole is a heterocyclic aromatic organic compound having a phenyl group and an imidazole group that share two carbon atoms in their ring structure. The general structure of benzimidazole is shown in the following formula (I):

[0057]

[0058] An example of a PBI polymer having one benzimidazole unit per repeating unit in the main chain is poly(2,5-benzimidazole) (AB-PBI), as shown in formula (II) below, and an example of a PBI polymer having two benzimidazole units per repeating unit in the main chain is poly[2,2′-(meta-phenylene)-5,5′-dibenzimidazole] (m-PBI), as shown in formula (III) below, and 4F-PBI (a fluorinated derivative of m-PBI), as shown in formula (IV) below.

[0059]

[0060] Other examples of PBI polymers include, but are not limited to, poly{2,6-(2,6-naphtyliden)-1,7-dihydrobenzo[1,2-d;4,5-d′]diimidazole}; poly-2,2′-(2,6-naphtyliden)-5,5′-dibenzimidazole; poly-2,2′-(2,6-pyridine ... 5-pyridine) 5,5'-bibenzimidazole; poly-2,2'-(2,2'-bipyridine-5,5')-5,5'-bibenzimidazole); poly-2,2'-(3,5-pyrazole)-5,5'-bibenzimidazole; poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole; poly-2,2'-(pyridylene-3",5")-5,5'-bibenzimidazole; poly-2,2'-(furanylene-2",5")-5,5'-bibenzimidazole; poly-2,2-(naphthalene-1",6")-5,5'-bibenzimidazole; poly-2 ,2′-(biphenylene-4",4")-5,5′-dibenzimidazole; poly-2,2′-pentylene-5,5'-dibenzimidazole; poly-2,2′-octylene-5,5'-dibenzimidazole; poly-2,6-(m-phenylene)-diimidazole benzene; poly-2,2′-cyclohexenyl-5,5'-dibenzimidazole; poly-2,2′-(m-phenylene)-5,5'-dibenzimidazole ether; poly-2,2′-(m-phenylene)-5,5-di(benzimidazole) sulfide; poly-2,2′-(m-phenylene)-5,5-di(benzo imidazole) sulfone; poly-2,2'-(m-phenylene)-5,5-di(benzimidazole)methane; poly-2-2"-(m-phenylene)-5",5"-(di(benzimidazole)propane 2.2; poly-2,2"-(m-phenylene)-5',5"-di(benzimidazole)ethylene-1,2; and derivatives (e.g., substituted (fluorinated) and / or branched derivatives) of any of the foregoing.

[0061] In some examples, the PBI polymer is a copolymer comprising one or more additional repeating units, which may or may not comprise benzimidazole units in the backbone, in the side chains, or in both.

[0062] In the PBI polymer molecule, the secondary amine group (e.g., N of the C-NH-C group) of the benzimidazole unit can be used to connect directly or indirectly with an ion exchanger to form an ion exchange functionalized PBI polymer molecule, wherein the PBI polymer molecule is functionalized with an ion exchange group. In a direct connection, the boron atom or metal atom of the ion exchange group is covalently bonded to the nitrogen atom of the secondary amine group. In some examples of indirect connection, the ion exchange group is connected to the secondary amine through a linker (e.g., an alkyl chain). In other examples of indirect connection, the ion exchange group is connected to the phenyl group of the benzimidazole unit through a sulfonic acid linker.

[0063] Exemplary ion exchange functionalized PBI polymer molecules and oligomer molecules, and methods of preparing ion exchange functionalized PBI polymer molecules and oligomer molecules will now be described. In the following description, discussion of polymer molecules and reference to polymer molecules are equally applicable to oligomer molecules, and discussion of polymer molecules and reference to polymer molecules can be extended to polymers (and oligomers) composed of the polymer molecules described herein.

[0064] Ion exchange functionalized PBI polymers and polymer molecules will now be described. However, the principles and concepts described herein are not limited to PBI polymers and polymer molecules, but can be applied to any polymer and polymer molecule having a benzimidazole unit, an imidazole unit, or a phenyl unit (in the case of indirect attachment) as at least a portion of the backbone, side chain, or both.

[0065] In some aspects, the ion exchange functionalized PBI polymer molecule (or oligomer molecule) comprises: (i) a repeating unit comprising a benzimidazole unit and optionally a phenyl unit; and (ii) at least one secondary amine attached to the benzimidazole unit and / or an ion exchange group attached to the phenyl unit.

[0066] The repeating unit of the ion exchange functionalized PBI polymer molecule comprises a benzimidazole unit as at least a portion of the main chain, as at least a portion of the side chain, or both. The benzimidazole unit comprises a benzimidazole group or its derivative, as explained above with reference to formula (I). The repeating unit may comprise any additional moieties and / or groups that can be used for a specific implementation. In some aspects, the repeating unit comprises a repeating unit of the above-mentioned PBI polymer molecule or its derivative. In some examples, for example in m-PBI (see formula (III)) and its derivatives, the repeating unit also comprises a single phenyl as at least a portion of the main chain, as at least a portion of the side chain, or both.

[0067] At least one ion exchange group includes a tetravalent boron group or a metal fluoride group containing a polyvalent metal atom. As used herein, "polyvalent" means that the atom is not limited to a specific number of valence bonds, but can have multiple different valence states, each of which has a different number of valence bonds. Therefore, a polyvalent trivalent atom can "expand its valence state", for example 1 to 3, to form a tetravalent, pentavalent or hexavalent structure with a negative one (-1), negative two (-2) or negative three (-3) formal charge. For example, boron has three valence electrons and has a 1s 2 2s 2 2p 1 The ground state electronic configuration of . Boron usually forms trivalent neutral compounds in which boron has three covalent bonds. Therefore, the boron atom is sp 2 Hybridized with an empty p-orbital, this makes trivalent boron compounds electron deficient. However, boron is multivalent due to the empty p-orbital, thus enabling boron to form negatively charged tetravalent compounds with four covalent bonds. Similarly, multivalent metal atoms can extend their valence to form one or more additional covalent bonds, thereby acquiring a formal negative charge, which can be balanced by an appropriate number of cations.

[0068] The tetravalent boron group has the general formula -BX3, wherein each X is independently an alkyl, alkoxy, alkoxycarbonyl, aryl, aryloxy, hydroxyl, fluoro, cyano or pentafluorophenyl. In the embodiment where each X is a fluoro group, the tetravalent boron group is a boron trifluoride group having the general formula -BF3.

[0069] The boron atom of the tetravalent boron group is covalently bonded to each X of the tetravalent boron group and to the secondary amine group of the benzimidazole unit or to the linker chain connecting the tetravalent boron group to the secondary amine group. Thus, the boron atom has four covalent bonds, making the boron atom ionic in nature. Therefore, the tetravalent boron group can act as an ion exchange group (e.g., a proton transporter).

[0070] The metal fluoride group has the general formula -MF3 or -MF4, wherein M is a polyvalent metal atom. As used herein, a "metal atom" may be a transition metal atom, a metal atom, or a metalloid atom. In some examples, M includes a Group 4 metal atom (e.g., zirconium (Zr)), a Group 13 metal atom (e.g., aluminum (Al), gallium (Ga) or indium (In)), or a Group 14 metal atom (e.g., silicon (Si), germanium (Ge) or tin (Sn)).

[0071] As mentioned, in some instances, the boron atom of the tetravalent boron group or the metal atom of the metal fluoride group is connected to the secondary amine group through a linker, such as an alkyl linker. In some instances, the linker is an alkyl group having 1 to 10 atoms, and optionally may be substituted with one or more side groups or side chains, each of which may independently be hydrogen, hydroxyl, fluoro, chloro, dialkylamino (NR2, wherein R may represent hydrogen or an organic binding group, such as methyl (CH3)), cyano, carboxylic acid, carboxyamide, ester, alkyl, alkoxy, or aryl.

[0072] In another example, the boron atom of the tetravalent boron group or the metal atom of the metal fluoride group is indirectly connected to the phenyl group of the repeating unit through a linker such as a sulfonate linker (e.g., a derivative of sulfonic acid). As will be explained below, the phenyl group can be activated by sulfonation with a pendant sulfonic acid group, which can be combined with an ion exchanger to form an ion exchange group.

[0073] The ion exchange functionalized PBI polymer molecules can be synthesized in any suitable manner. In some examples, the ion exchange functionalized PBI polymer molecules are synthesized by a post-polymerization process (eg, after the synthesis of the PBI polymer molecules).

[0074] In some examples, the post-polymerization process can be performed in a single step, wherein an ion exchanger is reacted with the PBI polymer molecules. The ion exchanger includes a trivalent boron compound or a metal fluoride and forms an ion exchange group when attached to the PBI polymer molecules.

[0075] The trivalent boron compound has the general formula BX3, wherein X is as described above. In the reaction, the boron atom of the trivalent boron compound expands its valence and covalently bonds with the nitrogen atom of the secondary amine of the benzimidazole unit, thereby forming an ion exchange group, wherein the boron atom is directly connected to the secondary amine of the benzimidazole unit.

[0076] The metal fluoride has the general formula MF3 or MF4, wherein M comprises a polyvalent metal atom, as described above. In the reaction, the polyvalent metal atom of the metal fluoride expands its valence and covalently bonds with the nitrogen atom of the secondary amine of the benzimidazole unit, thereby forming an ion exchange group, wherein the metal atom is directly connected to the secondary amine of the benzimidazole unit.

[0077] In other examples, the post-polymerization process for indirect attachment to secondary amines can be performed in a multi-step process. In the first step, a linker is reacted with a PBI polymer molecule. The linker bonds to the secondary amine of the benzimidazole unit and, when attached to the PBI polymer molecule, forms an intermediate linker having a chain length of 2 to 10 carbon atoms and presenting a pendant acid group or a pendant hydroxyl group.

[0078] In some instances, the linker includes a sulfonated compound. The sulfonated compound is an ester of sulfonic acid and has the general formula -S(=O)2OR, where R is an electron pair, hydrogen, alkyl or aryl. The sulfonated compound is connected to the secondary amine of benzimidazole to form a linker chain with a terminal sulfonic acid group. Exemplary examples of sulfonated compounds include, but are not limited to, methanesulfonate (mesylate), trifluoromethanesulfonate (trifluoromethanesulfonate), ethanesulfonate (esilate, esylate), toluenesulfonate (p-toluenesulfonate), benzenesulfonate (benzenesulfonate), chlorobenzenesulfonate (closilate) (chlorobenzenesulfonate (closylate), chlorobenzenesulfonate), camphorsulfonate (camsilate, camphorsulfonate (camsylate)) and pipsylate (p-iodobenzenesulfonate (ester) derivative).

[0079] In some examples, the sulfonated linker includes sultones. Sultones are cyclic sulfonate esters, many of which are 4- to 6-membered rings (having 2 to 4 carbon atoms), although some sultones are 7-membered rings or larger (having 5 or more carbon atoms). Sultones can react with primary and secondary amines, including the secondary amines of benzimidazoles. Illustrative examples of sultones include, but are not limited to, β-sultone, 1,3-propane sultone; 1,4-butane sultone; prop-1-ene-1,3-sultone; 3,4,4-trifluoro-3-(trifluoromethyl)oxathiane 2,2-dioxide; 3,3,4,4-tetrafluoro-1,2-oxathiane 2,2-dioxide; naphth[1,8-cd]-1,2-oxathiole, 2,2-dioxide; 5-methyl-1,2-oxathiolane 2,2-dioxide; 3-methyl-1,2-oxathiolane 2,2-dioxide; 2,2-dioxide); 1,2-oxathiine, 6-dodecyl-, 2,2-dioxide; 4,6-dimethyl-1,2-oxathiine 2,2-dioxide; acetyl fluoride, difluoride (fluorosulfonyl). The reaction of sultones with the secondary amine of the imidazole unit opens the alkyl linker chain with a terminal sulfonic acid group.

[0080] In other examples, the linking agent includes an alkyl linking agent, which reacts with a secondary amine and forms a linking group with a side acid group (e.g., a terminal carboxylic acid group, a phosphate group, a phosphonic acid group, a sulfonic acid group, a sulfate group, etc.) or a hydroxyl group (e.g., an alcohol linking group). In some examples, the alkyl linking agent has a carbon chain length of 2- to 10-. Exemplary alkyl linking agents include, but are not limited to, halogenated acids, alcohols, aldehydes, and ketones with side acid groups or terminal acid groups. In some examples, the alkyl linking agent includes a halogenated carboxylic acid, wherein the halogen is selected from chlorine, bromine, and iodine. Examples of halogenated carboxylic acids include, but are not limited to, bromoacetic acid and chloroacetic acid. The linking agent may be unsubstituted or substituted in whole or in part, as described above for the linking group. In some examples, the linking agent is substituted by fluorine (e.g., tetrafluoro β-sultone).

[0081] In the second step, an ion exchanger is reacted with the pendant acid group or the pendant hydroxyl group of the intermediate linker. The ion exchanger is easily reactive with the pendant acid group or the pendant hydroxyl group. The ion exchanger is as described above and forms an ion exchange group when connected to the PBI polymer molecule through the linker chain.

[0082] In some examples, the alkyl linker includes a halogenated alkylsulfonyl fluoride, such as a chloroalkylsulfonyl fluoride or a bromoalkylsulfonyl fluoride, which forms a first intermediate sulfonyl fluoride-terminated alkyl linker. Prior to performing the second step, the sulfonyl fluoride-terminated alkyl linker is activated to a sulfonic acid (by any suitable method), and then the second step is performed to react the ion exchanger with the sulfonic acid group.

[0083] In other examples, the post-polymerization process for indirectly connecting the phenyl of the ion exchange group to the PBI polymer (e.g., m-PBI) can be carried out with a multi-step process. In the first step, the PBI polymer is sulfonated (e.g., activated with sulfonic acid) at the phenyl unit to introduce the intermediate side sulfonic acid group. The PBI polymer can be sulfonated in any suitable manner. In some instances, by the direct sulfonation of the PBI polymer and a sulfonating agent such as sulfur trioxide (SO3) and / or sulfuric acid (H2SO4) combination, the PBI polymer is sulfonated.

[0084] In the second step, as described above, an ion exchanger is reacted with the pendant sulfonic acid groups. The ion exchanger readily reacts with the pendant sulfonic acid groups. The ion exchanger is as described above, and when attached to the PBI polymer molecule through the pendant sulfonic acid groups, an ion exchange group is formed.

[0085] The degree of functionalized PBI polymer molecules with ion exchange groups can be controlled as required. In some instances, the PBI polymer molecules include ionomer molecules, wherein about 15 mole % of repeating units (or benzimidazole units or phenyl units) are functionalized with ion exchange groups. In other examples, about 10 mole % of repeating units (or benzimidazole units or phenyl units) are functionalized with ion exchange groups. In other examples, about 5 mole % of repeating units (or benzimidazole units or phenyl units) are functionalized with ion exchange groups. In other examples, more than 15 mole % of the repeating units (or benzimidazole units or phenyl units) are functionalized with ion exchange groups, for example 20 mole % or more, 30 mole % or more, 50 mole % or more or 75 mole % or more.

[0086] In the above examples, the ion exchange functionalized PBI polymer is formed by post-polymerization functional modification of the PBI polymer. In other examples, the ion exchange functionalized PBI polymer can be formed by pre-polymerization functional modification of a monomer molecule comprising a benzimidazole group and optionally a phenyl group.

[0087] refer to Figures 1 to 4B, illustrative examples of ion exchange functionalized PBI polymers and reaction routes for synthesizing ion exchange functionalized PBI polymers will now be shown and described. The following examples are exemplary and non-limiting. In the accompanying drawings, only the benzimidazole unit in the repeating unit of the PBI polymer molecule is shown, but the repeating unit can have any other units and structures that can be used for a specific implementation.

[0088] Figure 1 An exemplary reaction route for synthesizing ion exchange functionalized PBI polymer molecules is shown. In the first step, a tetrafluoro β-sultone linker reacts with a secondary amine of a benzimidazole unit to form an intermediate linker chain. The intermediate linker chain is a perfluorinated 2-carbon chain with a terminal sulfonic acid group. In the second step, the sulfonic acid group is converted into a tetravalent boron group using BF3 (in the form of BF3 etherate (Et2O)), thereby producing an ion exchange functionalized PBI polymer molecule. The boron atom of the tetravalent boron group has a negative formal charge, and thus the ion exchange group is ionic in nature, thereby enabling ion (e.g., proton) exchange. Although Figure 1 The use of perfluorinated sultones is shown, but in alternative examples the sultone is non-fluorinated.

[0089] Figure 2 Another exemplary reaction route for the synthesis of ion exchange functionalized PBI polymer molecules is shown. Figure 2 Similar to Figure 1 , except in Figure 2 In the process, the linker is 1,3-propane sultone. In the first step, the 1,3-propane sultone linker reacts with the secondary amine of the benzimidazole unit to form an intermediate linker chain. The intermediate linker chain is a 3-carbon chain with a terminal sulfonic acid group. In the second step, the sulfonic acid group is converted into a tetravalent boron group using BF3 (in the form of BF3 etherate). The boron atom of the tetravalent boron group has a negative formal charge, so the ion exchange group is ionic in nature, thereby enabling ion (e.g., proton) exchange. Although Figure 2 The use of unsubstituted sultones is shown, but in alternative examples the sultones may be substituted, for example, with one or more fluorine atoms.

[0090] Figure 3 Another exemplary reaction route for the synthesis of ion exchange functionalized PBI polymer molecules is shown. Figure 3 Similar to Figure 1 , except in Figure 3In the process, the linker is 1,4-butane sultone. In the first step, the 1,4-butane sultone linker reacts with the secondary amine of the benzimidazole unit to form an intermediate linker chain. The intermediate linker chain is a 4-carbon chain with a terminal sulfonic acid group. In the second step, the sulfonic acid group is converted into a tetravalent boron group using BF3 etherate. The boron atom of the tetravalent boron group has a negative formal charge, so the ion exchange group is ionic in nature, thereby enabling ion (e.g., proton) exchange. Although Figure 3 The use of unsubstituted sultones is shown, but in alternative examples the sultone may be substituted, for example with one or more fluorine atoms.

[0091] Figure 4A Another exemplary reaction route for synthesizing ion exchange functionalized PBI polymer molecules is shown. Figure 1 4, except that the linker is boron trifluoride (in the form of BF3 etherate) and the boron trifluoride reacts directly with the secondary amine of the benzimidazole unit to form an ion exchange group (a tetravalent boron group having the general formula -BF3). The boron atom of the ion exchange group has a negative formal charge, so the ion exchange group is ionic and acidic in nature, thereby enabling ion (e.g., proton) exchange.

[0092] Figure 4B Another exemplary reaction route for the synthesis of ion exchange functionalized PBI polymer molecules is shown. Figure 4B Similar to Figure 4A , except in Figure 4B In, the ion exchange group is a trivalent boron compound with the general formula BXYZ, wherein X, Y and Z are identical or different, and each independently represents an alkyl, alkoxy, alkoxycarbonyl, aryl, aryloxy, hydroxyl, fluoro, cyano or pentafluorophenyl. The trivalent boron trifluoride directly reacts with the secondary amine of the benzimidazole group to form an ion exchange group (a tetravalent boron group with the general formula -BXYZ). The boron atom of the ion exchange group has a negative formal charge, so the ion exchange group is essentially ionic and acidic, thus ion (e.g., proton) exchange can be performed. The acidic properties of the tetravalent boron group can be adjusted by partially or completely replacing X group, Y group and Z group with a highly electronegative fluorine atom.

[0093] In other examples, the reaction routes of Examples 1 to 4B can be modified by using a metal fluoride (such as MF3 or MF4) instead of boron trifluoride or a trivalent boron compound as an ion exchanger. The metal fluoride can be any of the above-mentioned metal fluorides.

[0094] In some aspects, the first polymer molecule and the second polymer molecule can be cross-linked to form a cross-linked polymer composition using a tetravalent boron cross-linking group. The first polymer molecule can be any PBI polymer molecule, including any PBI polymer molecule described herein. In some instances, the second polymer molecule is the second PBI polymer molecule, which can be identical or different from the first PBI polymer molecule. In other examples, the second polymer molecule is a polymer molecule functionalized with an acid group (such as sulfonic acid, carboxylic acid, phosphoric acid, phosphonic acid) or hydroxyl. The example of acid-functionalized and hydroxyl-functionalized polymer molecules includes but is not limited to functionalized poly (tetrafluoroethylene) (PTFE) molecules, poly (phosphoric acid) (PPA) molecules, cellulose, lignin, etc.

[0095] The tetravalent boron crosslinking group has the general formula -BX2-, wherein each X is different or identical and independently is a hydroxyl or a halogen, such as fluorine or chlorine. The boron atom is covalently bonded to the secondary amine of the first PBI polymer molecule, and to the secondary amine, acid group or hydroxyl of the second polymer molecule. In this configuration, the boron atom is tetravalent and has a formal negative charge, thereby making the tetravalent boron crosslinking group ionic and acidic in nature. The tetravalent boron crosslinking group can therefore also serve as an ion (e.g., cation) exchange group.

[0096] In some examples, a method of cross-linking a PBI polymer molecule and a second polymer molecule includes combining the first PBI polymer molecule, the second polymer molecule, and a cross-linking agent comprising a trivalent boron compound.

[0097] Any suitable crosslinking agent that produces a tetravalent boron crosslinking group can be used. In some examples, the crosslinking agent is a boronic acid having the general formula B(OH)3, or an organic boronic acid having the general formula RB(OH)2, or a derivative of an organic boronic acid. Illustrative examples of the cross-linking agent include, but are not limited to, trimethyl borate, triethyl borate, tributyl borate, n-octyl borate, tridecyl borate, tritetradecyl borate, triisopropyl borate, trihexafluoroisopropyl borate, trimethoxycyclotriboroxane, triphenyl borate, tri-o-tolyl borate, tris(trimethylsilyl)borate, tetraacetyl diborate, tris(2,2,2-trifluoroethyl)borate, bis-pinacol diboronate, pinacolboronate, allylboronic acid pinacol ester, and diisopropoxymethylborane. The boron atom of the crosslinking agent is covalently bonded to the secondary amine of the first PBI polymer molecule and covalently bonded to the secondary amine, acid group or hydroxyl group of the second polymer molecule. Specifically, the boron atom extends its valence to covalently bond to the nitrogen of the secondary amine of the first PBI polymer molecule. The boron atom also reacts with the nitrogen atom of the secondary amine, acid group or hydroxyl group of the second polymer molecule by substitution reaction.

[0098] In some examples, fluoride treatment may be performed after cross-linking to replace hydroxyl groups with fluorine groups.

[0099] refer to Figures 5 to 7 , illustrative examples of cross-linked PBI polymer molecules and reaction routes for cross-linking PBI polymer molecules with another polymer molecule will now be shown and described. The following examples are exemplary only and not limiting. In the accompanying drawings, only the benzimidazole unit in the repeating unit of the PBI polymer molecule is shown, but the repeating unit may have any other units and structures that can be used for a specific implementation.

[0100] Figure 5 An exemplary reaction scheme for intramolecular crosslinking of two PBI polymer molecules using boric acid (B(OH)3) as a crosslinking agent is shown. Figure 5The reaction route is to crosslink the PBI polymer layer or sheet. In the first step, the PBI polymer molecule is combined with boric acid. Boric acid reacts with the secondary amine of the PBI polymer molecule to form a tetravalent boron crosslinking group with the general formula -B(OH)2-. The boron atom has four covalent bonds and thus obtains a negative formal charge, thereby making the tetravalent boron crosslinking group essentially ionic and acidic and capable of acting as an ion (e.g., cation) transport agent. In some instances, boric acid is a limiting agent to control the degree of crosslinking and the proton exchange capacity of the resulting ion exchange functionalized PBI polymer composition.

[0101] In an optional second step, the acidity of the tetravalent boron crosslinking groups is increased by fluoride treatment. The fluoride treatment can be performed in any suitable manner, such as by combining the crosslinked PBI polymer molecules with sodium fluoride (NaF).

[0102] Figure 6 An exemplary reaction route for crosslinking PBI polymer molecules with hydroxy-functionalized PTFE polymer molecules using boric acid as a crosslinking agent is shown. As shown, PTFE (represented by open circles) is functionalized with an acid group represented by X-OH, wherein X is a substituent containing a sulfur (S) atom, a carbon (C) atom, or a phosphorus (P) atom covalently bonded to an oxygen (O) atom of a hydroxyl group. The acid group X-OH can be any suitable acid group, such as, but not limited to, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a phosphonic acid group, or an alcohol. In some instances, the substituent X includes C1 to C 30 The alkyl group links the chain and optionally has one or more side groups, which can be the same or different and can be independently selected from hydrogen, hydroxyl, fluoro, chloro, dialkylamino, cyano, carboxylic acid, carboxyamide, ester, alkyl, alkoxy, and aryl. In some examples, the substituent X can be omitted so that the PTFE is functionalized only with hydroxyl groups. Although Figure 6 The PTFE is shown functionalized with only one acid group, X-OH, but the PTFE can have any degree of functionalization useful for a particular implementation.

[0103] In the first step, PBI polymer molecules and acid-functionalized PTFE polymer molecules are combined with boric acid. Boric acid reacts with the secondary amine of the first PBI polymer molecule and reacts with the hydroxyl of the functionalized PTFE to form a tetravalent boron crosslinking group with the general formula -B(OH)2-. The boron atom has four covalent bonds and thus obtains a negative formal charge, thereby making the tetravalent boron crosslinking group essentially ionic and acidic and capable of acting as an ion (e.g., cation) transport agent. In some instances, boric acid is a limiting agent to control the degree of crosslinking and the proton exchange capacity of the resulting ion exchange functionalized PBI / PTFE polymer composition.

[0104] In an optional second step, the acidity of the tetravalent boron crosslinking groups is increased by fluoride treatment, for example by combining the crosslinked PBI / PTFE polymer molecules with sodium fluoride (NaF).

[0105] Although Figure 6 The PBI polymer molecules are shown crosslinked with functionalized PTFE polymer molecules, but the PBI polymer molecules can be crosslinked in a similar manner with any other suitable acid- or hydroxyl-functionalized polymer, such as synthetic polymers such as poly(phosphoric acid) (PPA) or natural polymers such as lignin, cellulose, chitin, etc. For example, the PBI polymer can be crosslinked with a polymer doped with PPA. The crosslinked PBI polymer prevents or reduces leaching of the PPA dopant from the polymer doped with PPA.

[0106] exist Figure 5 and Figure 6 In the example of , boric acid is used to crosslink two polymer molecules. In variations of these reaction routes, a boronic acid derivative such as an organic boronic acid (e.g., (RB(OH)2 or (R 1 -B(OH)-R 2 ) or trivalent boron having the general formula BXYZ, can crosslink two polymer molecules, as described above with respect to Figure 4B described.

[0107] Figure 7 An exemplary reaction scheme for cross-linking PBI polymer molecules with functionalized PTFE polymer molecules using an aminoorganoboronic acid as a cross-linking agent is shown.

[0108] In the first step 702, sulfonyl fluoride functionalized PTFE 704 (PTFE backbone is represented by open circles) is combined with 4-aminophenyl organoboric acid 706. Sulfonyl fluoride functionalized PTFE 704 forms a strong covalent bond with the amino organoboric acid to form an intermediate amino organoboric acid functionalized PTFE polymer molecule 708. Non-aqueous bases may optionally be added to capture hydrogen fluoride (HF), thus helping to shift the reaction equilibrium to the right (towards the product). It will be appreciated that any other suitable amino organoboric acid or its derivatives may be used, including but not limited to aminophenyl, aminoaryl and aminoalkyl organoboric acids or organoboric acid substitutes, such as boronic acid pinacolates.

[0109] In a second step 710, the aminoboronic acid functionalized PTFE polymer molecules 708 are combined with PBI polymer molecules 712. The boronic acid groups of the aminoboronic acid functionalized PTFE polymer molecules 708 react with the secondary amines of the PBI polymer molecules 712, thereby crosslinking the PBI polymer molecules 708 with the functionalized PTFE polymer molecules 704. The boron atom of the tetravalent boron crosslinking group has four covalent bonds and thus acquires a negative formal charge, thereby making the tetravalent boron crosslinking group ionic and acidic in nature and capable of acting as an ion (e.g., cation) transport agent.

[0110] In an optional third step 714, the acidity of the tetravalent boron crosslinking groups can be increased by fluoride treatment, for example by combining the crosslinked polymer molecules with sodium fluoride (NaF).

[0111] Although Figure 7 PBI polymer molecules 712 are shown cross-linked with functionalized PTFE polymer molecules 704, but PBI polymer molecules 712 may be cross-linked in a similar manner with any other suitable activated polymer molecules, including but not limited to synthetic or natural polymer molecules.

[0112] like Figure 7 As shown, the reaction route starts with a sulfonyl fluoride functionalized PTFE polymer molecule 704. In other examples (not shown), the reaction route can start with a sulfonic acid functionalized PTFE polymer molecule (or other polymer molecule). However, since the sulfonic acid group is usually not directly covalently bonded to the primary amine of the aminoorganoboric acid, the sulfonic acid group is activated as a sulfonyl fluoride group (SO2F) for the reaction with the primary amine of the aminoorganoboric acid. Alternatively, the sulfonic acid group can be activated as a sulfonyl chloride group (SO2Cl) for the reaction with the primary amine of the aminoorganoboric acid.

[0113] Figure 8 An exemplary reaction route for intramolecular crosslinking of PBI polymer molecules with PPA polymer molecules using boric acid as a crosslinking agent is shown. PPA has a general structure as shown in the following formula (V):

[0114]

[0115] In some examples, PPA is used as a dopant to improve the cation conductivity of PBI polymers such as 4F-PBI. However, direct attachment of PPA to PBI occurs through only weak, balanced acid-base interactions between the acidic phosphates of PPA and the basic imidazole nitrogen atoms of PBI. As a result, acidic phosphate residues are leached from the PEM and ionomer, thereby reducing the cation exchange properties of the PBI polymer. To improve the performance of PBI / PPA polymers, the PBI polymer can be crosslinked with the PPA polymer using tetravalent boron crosslinking groups, such as Figure 8 Note that Figure 8 In the example of FIG. 1 , only the repeating units of the PPA polymer molecule are shown. However, the degree of cross-linking can be controlled as desired.

[0116] like Figure 8 As shown, in the first step, the PBI polymer molecule and the PPA polymer molecule are combined with boric acid. Boric acid reacts with the secondary amine of the PBI polymer molecule and reacts with the hydroxyl of the PPA polymer molecule to form a tetravalent boron crosslinking group with the general formula -B(OH)2-. In addition to two hydroxyl groups, the boron atom is also bonded to the nitrogen of the secondary amine and the oxygen atom of the PPA molecule. Therefore, the boron atom has four covalent bonds and obtains a negative formal charge. As a result, the tetravalent boron crosslinking group is essentially ionic and acidic and can act as an ion (e.g., cation) transport agent. In addition, the crosslinking by the tetravalent boron atom occurs through multiple boron-oxygen bonds, thereby strongly binding to PPA and increasing robustness and minimizing the leaching of PPA. In some instances, boric acid is a limiting agent to control the degree of crosslinking and the proton exchange capacity of the resulting ion exchange functionalized PBI / PPA composition.

[0117] In an optional second step, the acidity of the tetravalent boron crosslinking groups is increased by fluoride treatment, for example by combining the crosslinked PBI / PPA polymer molecules with sodium fluoride (NaF).

[0118] exist Figure 8 In the example of the present invention, boric acid is used to crosslink the PBI polymer molecules and the PPA polymer molecules. In a variation of this reaction route, a boronic acid derivative such as an organic boronic acid (e.g., (RB(OH)2 or (R 1 -B(OH)-R 2 ) or trivalent boron having the general formula BXYZ, can crosslink the PBI polymer molecules and the PPA polymer molecules, as described above with respect to Figure 4B described.

[0119] The ion exchange functionalized PBI polymers and polymer compositions described herein include tetravalent boron-crosslinked polymer compositions that can be formed into porous polymer networks and / or can be used as ionomers, membranes and / or PEMs. The polymers, ionomers and membranes (e.g., PEMs) described herein can be used in water electrolysis systems and fuel cells, as well as in batteries (e.g., as separation membranes) and in the production of ammonia (e.g., for the production of H2 as a precursor for the Haber-Bosch process and / or for the generation of electricity for separation of nitrogen from air and / or for use during the Haber-Bosch process). Reference will now be made to Fig. 9 and Fig.10 To describe exemplary applications of the ion exchange functionalized PBI polymer.

[0120] Fig. 9 An exemplary proton exchange membrane water electrolysis system 900 (PEM water electrolysis system 900) is shown. The PEM water electrolysis system 900 uses electricity to decompose water into oxygen (O2) and hydrogen (H2) via an electrochemical reaction. The configuration of the PEM water electrolysis system 900 is exemplary only and not limiting, as other suitable configurations and other suitable water electrolysis systems may incorporate a boron-containing porous membrane.

[0121] like Fig. 9 As shown in FIG. 9 , the PEM water electrolysis system 900 includes a membrane electrode assembly 902 (MEA 902), porous transport layers 904-1 and 904-2, bipolar plates 906-1 and 906-2, and a power supply 908. The PEM water electrolysis system 900 may also include Fig. 9 Additional or alternative components not shown may be used in particular implementations.

[0122] MEA 902 includes a PEM 910 located between a first catalyst layer 912-1 and a second catalyst layer 912-2. PEM 910 electrically isolates the first catalyst layer 912-1 from the second catalyst layer 912-2, while providing cations such as protons (H + ) and at the same time is impermeable to gases such as hydrogen and oxygen. PEM 910 can be implemented by any suitable PEM, including any PEM described herein. For example, PEM 910 can be implemented by an ion exchange functionalized PBI polymer described herein.

[0123] The first catalyst layer 912-1 and the second catalyst layer 912-2 are conductive electrodes with embedded electrochemical catalysts (not shown) such as platinum, ruthenium, and / or cerium (IV) oxide. In some examples, the first catalyst layer 912-1 and the second catalyst layer 912-2 are formed using ionomers in combination with catalyst nanoparticles. The ionomers used to form the first catalyst layer 912-1 and the second catalyst layer 912-2 may include ion exchange functionalized PBI polymers as described herein.

[0124] MEA 902 is positioned between porous transport layers 904 - 1 and 904 - 2 , which in turn are positioned between bipolar plates 906 - 1 and 906 - 2 , with flow channels 914 - 1 and 914 - 2 located between bipolar plate 906 and porous transport layer 904 .

[0125] In MEA 902, the first catalyst layer 912-1 acts as an anode and the second catalyst layer 912-2 acts as a cathode. When the PEM water electrolysis system 900 is powered by power supply 908, an oxygen evolution reaction (OER) occurs at the anode 912-1 represented by the following electrochemical half-reaction:

[0126] 2H2O→O2+4H + +4e -

[0127] Protons are conducted from anode 912-1 to cathode 912-2 through PEM 910, and electrons are conducted from anode 912-1 to cathode 912-2 through a conduction path bypassing PEM 910. PEM 910 allows protons (H + ) and water are transported from the anode 912-1 to the cathode 912-2, but is impermeable to oxygen and hydrogen. At the cathode 912-2, the protons combine with electrons in a hydrogen evolution reaction (HER) represented by the following electrochemical half-reaction:

[0128] 4H + +4e - →2H2

[0129] The OER and HER are two complementary electrochemical reactions for splitting water by electrolysis, represented by the following overall water electrolysis reaction:

[0130] 2H2O→2H2+O2

[0131] Fig.10An exemplary proton exchange membrane fuel cell 1000 (PEM fuel cell 1000) including a boron-containing porous membrane is shown. The PEM fuel cell 1000 generates electricity due to an electrochemical reaction. In this example, the electrochemical reaction involves reacting hydrogen (H2) and oxygen (O2) to produce water and electricity. The configuration of the PEM fuel cell 1000 is exemplary only and not limiting, as other suitable configurations and other suitable proton exchange membrane fuel cells may incorporate the boron-containing porous membrane.

[0132] like Fig.10 As shown in FIG. 1 , PEM fuel cell 1000 includes membrane electrode assembly 1002 (MEA 1002), porous transport layers 1004-1 and 1004-2, bipolar plates 1006-1 and 1006-2. Electrical load 1008 may be electrically connected to MEA 1002 and driven by PEM fuel cell 1000. PEM fuel cell 1000 may also include Fig.10 Additional or alternative components not shown may be used in particular implementations.

[0133] MEA 1002 includes a PEM 1010 located between a first catalyst layer 1012-1 and a second catalyst layer 1012-2. PEM 1010 electrically isolates the first catalyst layer 1012-1 from the second catalyst layer 1012-2, while providing cations such as protons (H + ) and at the same time is impermeable to gases such as hydrogen and oxygen. PEM 1010 can be implemented by any suitable PEM, including any PEM described herein. For example, PEM 1010 can be implemented by an ion exchange functionalized PBI polymer described herein.

[0134] The first catalyst layer 1012-1 and the second catalyst layer 1012-2 are conductive electrodes with embedded electrochemical catalysts (not shown). In some examples, the first catalyst layer 1012-1 and the second catalyst layer 1012-2 are formed using ionomers in combination with catalyst nanoparticles. In some examples, the ionomers used to form the first catalyst layer 1012-1 and the second catalyst layer 1004-2 include ion exchange functionalized PBI polymers as described herein.

[0135] MEA 1002 is placed between porous transport layer 1004-1 and porous transport layer 1004-2, which are further placed between bipolar plate 1006-1 and bipolar plate 1006-2, with flow channel 1014 located therebetween. In MEA 1002, first catalyst layer 1012-1 acts as a cathode, and second catalyst layer 1012-2 acts as an anode. Cathode 1012-1 and anode 1012-2 are electrically connected to load 1008, and load 1008 is driven by electricity generated by PEM fuel cell 1000.

[0136] During operation of the PEM fuel cell 1000, hydrogen (H2) flows into the anode side of the PEM fuel cell 1000, while oxygen (O2) flows into the cathode side of the PEM fuel cell 1000. At the anode 1012-2, hydrogen molecules are catalytically split into protons (H + ) and electron (e - ):

[0137] 2H2→4H + +4e -

[0138] The protons are conducted from the anode 1012-2 to the cathode 1012-1 through the PEM 1010, and the electrons are conducted from the anode 1012-2 to the cathode 1012-1 through the conduction path and the load 1008, bypassing the PEM 1010. At the cathode 1012-1, the protons and electrons combine with oxygen according to the following oxygen reduction reaction (ORR):

[0139] O2+4H + +4e - →2H2O

[0140] Therefore, the overall electrochemical reaction of the PEM fuel cell 1000 is:

[0141] 2H2+O2→2H2O

[0142] In the overall reaction, the PEM fuel cell 1000 produces water at the cathode 1012-1. The water can flow from the cathode 1012-1 to the anode 1012-2 through the PEM 1010 and can be removed through an outlet on the cathode side and / or the anode side of the PEM fuel cell 1000. The overall reaction produces electrons at the anode that drive the load 1008.

[0143] In the foregoing description, various exemplary embodiments have been described with reference to the accompanying drawings. However, it is apparent that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the scope of the appended claims. For example, certain features of one embodiment described herein may be combined or replaced with features of another embodiment described herein. Therefore, the description and drawings should be regarded as illustrative rather than restrictive.

Claims

1. An ion exchange functionalized polymer molecule comprising: A repeating unit comprising a benzimidazole unit as at least a part of the main chain, the side chain, or both; and An ion exchange group is attached to the repeating unit, wherein the ion exchange group comprises a tetravalent boron group or a metal fluoride comprising a multivalent metal atom.

2. The ion exchange functionalized polymer molecule according to claim 1, wherein The repetition of the repeating unit constitutes 4F-PBI.

3. The ion exchange functionalized polymer molecule according to claim 1, wherein The ion exchange group includes the tetravalent boron group.

4. The ion exchange functionalized polymer molecule according to claim 3, wherein The tetravalent boron group includes a boron trifluoride group.

5. The ion exchange functionalized polymer molecule according to claim 3, wherein The tetravalent boron group has the general formula -BX3, wherein each X independently comprises an alkyl group, an alkoxy group, an alkoxycarbonyl group, an aryl group, an aryloxy group, a hydroxyl group, a fluoro group, a cyano group or a pentafluorophenyl group.

6. The ion exchange functionalized polymer molecule according to claim 3, wherein The boron atom of the tetravalent boron group is covalently bonded to the nitrogen atom of the secondary amine of the benzimidazole unit.

7. The ion exchange functionalized polymer molecule according to claim 1, wherein The ion exchange group includes the metal fluoride.

8. The ion exchange functionalized polymer molecule according to claim 7, wherein The polyvalent metal atom includes a Group 4 metal, a Group 13 metal, or a Group 14 metal.

9. The ion exchange functionalized polymer molecule according to claim 7, wherein The polyvalent metal atom includes zirconium (Zr), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), or tin (Sn).

10. The ion exchange functionalized polymer molecule according to claim 7, wherein The polyvalent metal atom is covalently bonded to the nitrogen atom of the secondary amine.

11. The ion exchange functionalized polymer molecule of claim 1, wherein: The boron atom of the tetravalent boron group or the polyvalent metal atom is covalently bonded to the nitrogen atom of the secondary amine of the benzimidazole unit.

12. The ion exchange functionalized polymer molecule of claim 1, wherein: The ion exchange group is connected to the phenyl unit of the repeating unit.

13. The ion exchange functionalized polymer molecule of claim 1, wherein: The ion exchange group is connected to the secondary amine of the benzimidazole unit via a linker.

14. The ion exchange functionalized polymer molecule of claim 13, wherein: The linking group comprises an alkyl chain having from 2 to 10 atoms in the backbone of the alkyl chain.

15. The ion exchange functionalized polymer molecule of claim 14, wherein The linker is fluorinated.

16. A method for preparing an ion exchange functionalized polymer molecule comprising: The ion exchanger is attached to the repeating unit of the polymer molecule, wherein: The polymer molecule comprises a benzimidazole unit as at least a part of the main chain or side chain of the polymer molecule; and The ion exchanger includes a trivalent boron compound or a metal fluoride containing a polyvalent metal atom.

17. The method according to claim 16, wherein: The polymer molecules include polybenzimidazole (PBI) polymer molecules.

18. The method according to claim 17, wherein: The PBI polymer molecule includes 4F-PBI.

19. The method according to claim 16, wherein: The ion exchanger includes the trivalent boron compound.

20. The method according to claim 19, wherein: The trivalent boron compound includes boron trifluoride.

21. The method according to claim 19, wherein: The trivalent boron compound has a general formula -BX3, wherein each X independently comprises an alkyl group, an alkoxy group, an alkoxycarbonyl group, an aryl group, an aryloxy group, a hydroxyl group, a fluoro group, a cyano group or a pentafluorophenyl group.

22. The method according to claim 19, wherein: Attaching the ion exchanger to the repeating unit includes covalently bonding a boron atom of the trivalent boron compound to a nitrogen atom of a secondary amine of the benzimidazole unit.

23. The method according to claim 16, wherein: The ion exchanger includes the metal fluoride.

24. The method according to claim 23, wherein: The polyvalent metal atom includes a Group 4 metal, a Group 13 metal, or a Group 14 metal.

25. The method according to claim 23, wherein: The polyvalent metal atom includes zirconium (Zr), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), or tin (Sn).

26. The method of claim 23, wherein: Attaching the ion exchanger to the repeating unit includes covalently bonding the multivalent metal atom of the metal fluoride to the nitrogen atom of the secondary amine of the benzimidazole unit.

27. The method of claim 16, wherein: Connecting the ion exchanger to the repeating unit comprises: forming an intermediate linker connected to the secondary amine of the benzimidazole unit, wherein the intermediate linker comprises a pendant acid group or a pendant hydroxyl group; and The ion exchanger is reacted with the pendant acid group or the pendant hydroxyl group.

28. The method according to claim 27, wherein: The pendant acid groups include sulfonic acid groups.

29. The method according to claim 27, wherein: The intermediate linking group comprises an alkyl chain having from 2 to 10 atoms in the backbone of the alkyl chain.

30. The method of claim 27, wherein: Forming the intermediate linker includes bonding a linker to the secondary amine.

31. The method according to claim 30, wherein: The linking agent includes a sulfonated compound.

32. The method of claim 30, wherein: The linking agent includes sultone.

33. The method of claim 16, wherein: Connecting the ion exchanger to the repeating unit comprises: forming an intermediate linker comprising a pendant sulfonic acid group attached to a phenyl unit of the repeating unit; and The ion exchanger is reacted with the pendant sulfonic acid group of the intermediate linker.

34. A polybenzimidazole (PBI) polymer comprising: A backbone comprising benzimidazole units; and an ion exchange group connected to the benzimidazole unit; The ion exchange groups include tetravalent boron groups or metal fluoride groups, each of which contains a multivalent metal atom.

35. The PBI polymer of claim 34, further comprising a side chain bonded to the secondary amine of the benzimidazole unit, wherein the ion exchange group is contained in the side chain.

36. The PBI polymer of claim 34, wherein The ion exchange group includes the tetravalent boron group attached to the secondary amine of the benzimidazole unit.

37. The PBI polymer of claim 34, wherein The ion exchange groups include the metal fluoride groups attached to the secondary amines of the benzimidazole units.

38. A polymer composition comprising a first polymer crosslinked to a second polymer via a tetravalent boron crosslinking group, the first polymer comprising a first polybenzimidazole (PBI) polymer.

39. The polymer composition according to claim 38, wherein The first PBI polymer includes 4F-PBI.

40. The polymer composition of claim 38, wherein The second polymer includes a second PBI polymer.

41. The polymer composition of claim 38, wherein The second polymer includes an acid-functionalized or hydroxy-functionalized polymer.

42. The polymer composition according to claim 41, wherein The second polymer includes a poly(phosphoric acid) (PPA) polymer.

43. The polymer composition of claim 38, wherein The tetravalent boron crosslinking groups include boron atoms covalently bonded to nitrogen atoms of benzimidazole units of the first PBI polymer.

44. The polymer composition of claim 38, wherein The tetravalent boron crosslinking groups are fluorinated.

45. A method for cross-linking a first polymer and a second polymer using a tetravalent boron cross-linking group, the method comprising: reacting the first polymer, the second polymer, and a cross-linking agent, wherein: The first polymer includes a first polybenzimidazole (PBI) polymer, the first polybenzimidazole (PBI) polymer comprising benzimidazole units as at least a portion of the backbone; and The cross-linking agent includes boric acid, boronic acid, or a derivative of boronic acid.

46. ​​The method of claim 45, wherein: The first PBI polymer includes 4F-PBI.

47. The method of claim 45, wherein: The second polymer includes a second PBI polymer.

48. The method of claim 45, wherein: The second polymer includes an acid-functionalized or hydroxy-functionalized polymer.

49. The method of claim 48, wherein: The second polymer includes a poly(phosphoric acid) (PPA) polymer.

50. The method of claim 45, wherein: The tetravalent boron crosslinking groups include boron atoms covalently bonded to nitrogen atoms of benzimidazole units of the first PBI polymer.

51. The method of claim 45, further comprising: The tetravalent boron crosslinking group is subjected to a fluoride treatment.

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