Boric acid-functionalized carbon material

Abstract

A boronic acid-functionalized carbon material includes a carbon material and boronic acid groups attached to a surface of the carbon material. The carbon material can include carbon black, graphite, or graphene. The boronic acid groups include trivalent boronic acid groups and / or tetravalent boronic acid groups. The boronic acid-functionalized carbon material can be used as a catalyst support, a catalyst binder, and / or an ionomer for cation transport.

Description

Related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 604,311, filed November 30, 2023 (which is hereby incorporated in its entirety by reference). Background Technology

[0002] In some electrochemical cells (e.g., hydrogen fuel cells) and water electrolysis systems, proton exchange membranes (PEMs) are used to selectively transport protons. A PEM is a semi-permeable membrane that transports protons (H+). + It is also impermeable to gases. PEMs typically consist of a porous framework with highly acidic functional groups. For example, polyfluorosulfonic acid (PFSA) based PEMs (e.g., Nafion PEMs). TM (The Chemours Company, Wilmington, Delaware) and Aquivion® (Solvay SA Corporation, Brussels, Belgium) contain a porous polytetrafluoroethylene (PTFE) framework with sulfonic acid side groups. The easily dissociable sulfonic acid groups serve as proton transport agents in the membrane. In a hydrogen fuel cell, hydrogen (H2) is separated into protons (H+) at the anode. + Protons pass through the PEM and combine with oxygen (O2) at the cathode to produce water, while electrons flow through the external circuit to generate electricity. In a water electrolysis system, electricity splits water at the anode into oxygen (O2) and protons (H+). + Protons pass through the PEM and combine with electrons at the cathode to produce hydrogen gas (H2).

[0003] A membrane electrode assembly (MEA) may include a PEM located between a first catalyst layer and a second catalyst layer. The catalyst layers are conductive electrodes (anode and cathode) with embedded electrochemical catalyst particles (e.g., metals, metal alloys, or metal oxides). The catalyst particles may be supported on a catalyst solid support, which typically comprises a conductive carbon material with a high specific surface area (e.g., carbon black, graphite, or graphene). The electrochemical catalyst lowers the activation energy required for electrochemical reactions to occur at the electrodes, such as the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in water electrolysis applications, and the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in fuel cell applications.

[0004] In some applications, the catalyst layer comprises 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 layered onto the PEM in an MEA stack. In other MEAs, the catalyst layer is coated onto the PEM to form a catalyst-coated membrane (CCM).

[0005] Water electrolysis and fuel cell applications involve strong oxidizing and reducing chemical reactions under conditions ranging from ambient to high temperatures and acidic environments. Therefore, the materials used in electrochemical cells (e.g., PEM, ionomers, catalysts, catalyst supports, electrodes, and gas diffusion layers) must remain robust under harsh redox stress reaction conditions. Summary of the Invention

[0006] The following description presents a simplified overview of one or more aspects of the devices, compositions, and / or methods described herein to provide a basic understanding of these aspects. This overview is not a comprehensive summary of all anticipated aspects and is neither intended to identify major or key elements of all aspects nor to indicate the scope of any aspect or all aspects. Its sole purpose is to present, in a simplified form, some ideas of one or more aspects of the devices, compositions, and / or methods described herein as an introduction to the more detailed descriptions presented below.

[0007] In some illustrative examples, boronic acid-functionalized carbon materials comprise: carbon material; and boronic acid groups attached to the surface of the carbon material.

[0008] In some illustrative examples, a method for preparing boric acid-functionalized carbon materials includes reacting oxidized carbon materials with a boronic compound to form trivalent boric acid-functionalized carbon materials, said trivalent boric acid-functionalized carbon materials comprising trivalent boric acid groups attached to the surface of said carbon materials.

[0009] In some illustrative examples, the method also includes fluoridating the trivalent boric acid-functionalized carbon material to convert the trivalent boric acid groups into tetravalent boric acid groups.

[0010] In some illustrative examples, the catalyst support comprises: a carbon material; and borate groups attached to the surface of the carbon material.

[0011] In some illustrative examples, the gas diffusion layer for an electrochemical cell comprises: a carbon material; and borate groups attached to the surface of the carbon material. Attached Figure Description

[0012] The accompanying drawings illustrate various embodiments and are part of the specification. The illustrated embodiments are merely examples and do not limit the scope of this disclosure. Throughout the drawings, the same or similar reference numerals designate the same or similar elements.

[0013] Figure 1 An illustrative reaction scheme for synthesizing oxidized carbon materials is shown.

[0014] Figure 2 An illustrative reaction scheme for synthesizing boric acid-functionalized carbon materials is shown, wherein the boric acid-functionalized carbon materials have trivalent boric acid groups on the surface of the carbon materials.

[0015] Figure 3 An illustrative reaction scheme for synthesizing boric acid-functionalized carbon materials is shown, wherein the boric acid-functionalized carbon materials have both trivalent and tetravalent boric acid groups on the surface of the carbon material.

[0016] Figure 4 Another illustrative reaction scheme for the one-pot synthesis of boric acid-functionalized carbon materials with tetravalent boric acid groups is shown.

[0017] Figure 5 An illustration of a proton exchange membrane water electrolysis system is shown.

[0018] Figure 6 This illustrates a proton exchange membrane fuel cell. Detailed Implementation

[0019] This article describes boric acid-functionalized carbon materials, including boric acid-functionalized carbon black, boric acid-functionalized graphite, and boric acid-functionalized graphene. These boric acid-functionalized carbon materials can be used in a variety of applications, including in electrochemical cells, such as water electrolysis systems and / or fuel cell systems.

[0020] Various definitions will now be provided to aid in understanding the various aspects of this disclosure. The terms or expressions used herein (e.g., alkyl, m, n, etc.) are intended to be used independently of their definitions elsewhere in this disclosure. In the event of any conflict with any patent application or patent incorporated herein by reference, this specification (including the definitions) shall prevail.

[0021] As used herein, "polymer" refers to a substance comprising polymer molecules of the same or different polymer species, including mixtures of polymer molecules of the same polymer species, wherein the polymer molecules 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.

[0022] As used herein, “polymer molecule” or “macromolecule” refers to a molecule with a high relative molecular mass whose structure comprises a relatively large number of repeating units (e.g., about 60 or more monomer units) that are actually or conceptually derived from molecules with a low relative molecular mass (e.g., monomer molecules).

[0023] As used in this article, “oligomers” refers to substances composed of oligomer molecules.

[0024] As used herein, “oligomery” refers to a molecule of medium relative molecular mass whose structure comprises a relatively small number of repeating units (e.g., about 5 to about 60 monomer units) that are actually or conceptually derived from molecules of lower relative molecular mass (e.g., monomer molecules).

[0025] The principles, concepts, and characteristics described herein regarding polymers, polymer molecules, and polymerizations also apply to oligomers, oligomer molecules, and oligomers, respectively. Therefore, without departing from the scope of this disclosure, any and all uses of the terms polymer, polymer molecule, and polymerization herein may be replaced by the terms oligomer, oligomer molecule, and oligomer, respectively.

[0026] As used in this article, "ionomer" refers to a polymer composed of ionomer molecules.

[0027] As used herein, “ionomer molecules” refers to polymer molecules in which a small but relatively significant proportion of the structural units have ionizable pendant groups or ionic pendant groups (including the ion exchange groups described herein) or both. Typically, no more than about 15 mol% of the structural units have ionizable pendant groups or ionic pendant groups (e.g., sulfonic acid groups, carboxylic acid groups, phosphate groups, borate groups, etc.).

[0028] As used herein, "catalyst particles" refers to particles that are "black" or in pure form (e.g., excluding any catalyst support to which the catalyst particles can be bound and excluding any catalyst additives), which can increase the reaction rate without altering the total standard Gibbs free energy change in the reaction. Catalyst particles can be single molecules (including but not limited to monomer molecules), molecular groups, crystal structures (e.g., in metal oxides), polymer molecules, or oligomer molecules. Catalyst particles can have any suitable size and shape (e.g., microparticles, nanoparticles, or nanotubes). Catalyst particles can include, for example, metals, metal alloys, metal oxides, metal halides (e.g., metal chlorides), or composite materials, said composite materials including at least one of metals, metal alloys, metal oxides, or metal halides.

[0029] As used herein, “electrocatalyst particles” or “electrochemical catalyst particles” refer to catalyst particles that reduce the activation energy required to carry out an electrochemical reaction and / or increase the rate of an electrochemical reaction, such as OER, HER, HOR, and / or ORR. Suitable electrocatalyst particles may include, but are not limited to, metals, such as platinum group metals (PGMs) (e.g., platinum, palladium, iridium, ruthenium, osmium, and rhodium), transition metals (e.g., silver, gold, cobalt, copper, iron, nickel, rhenium, and mercury), and post-transition metals (e.g., bismuth and tin); metal alloys (e.g., PGM-transition metal based alloys and platinum-ruthenium based alloys); metal oxides (e.g., PGM oxides, such as iridium(IV), ruthenium(IV), iridium-ruthenium oxide, platinum(IV), magnesium oxide, and cerium(IV)); metal halides (e.g., platinum(IV), iridium(III), platinum(IV), iridium(III)); and / or composites of metals, metal alloys, metal oxides, and / or metal halides.

[0030] As used herein, “catalyst support” refers to a substance (excluding catalyst particles) that can be used to support catalyst particles (e.g., a substance or material to which catalyst particles can be bound, or a substance or material on which catalyst particles can be supported). Examples of catalyst supports include, but are not limited to: carbon-based materials (e.g., carbon black, graphite, carbon nanotubes, graphene, and / or boric acid-functionalized carbon materials as described herein), titanium dioxide, Sb-doped SnO2 nanoparticles, tin-doped indium oxide (ITO), and / or ion-exchange modified catalyst supports described in International Patent Application No. PCT / US2022 / 046105, filed October 7, 2022 (the contents of which are incorporated herein by reference in their entirety).

[0031] As used herein, “catalyst” refers to catalyst particles, as well as catalyst particles and catalyst supports (on which the catalyst particles are loaded or bound). Catalysts may also include catalyst additives, such as co-catalysts (e.g., but not limited to metalloids).

[0032] As used herein, “electrocatalyst” or “electrochemical catalyst” refers to electrocatalyst particles in “black” or pure form, as well as electrocatalyst particles and catalyst supports (on which the electrocatalyst particles are supported or bound). Electrocatalysts may also include catalyst additives (e.g., co-catalysts).

[0033] The term "metal" as used in this article includes alkali metals, alkaline earth metals, transition metals, lanthanides, actinides, and post-transition metals.

[0034] The term "transition metal" as used in this article refers to elements in the d-block of the periodic table (groups 3 to 12).

[0035] The term "post-transition metals" as used in this article refers to aluminum, gallium, indium, tin, thallium, lead, bismuth, and polonium.

[0036] The term "metalloids" as used in this article refers to boron, silicon, germanium, arsenic, antimony, tellurium, and astatine.

[0037] As used in this article, "platinum group metals" or "PGM" refers to platinum, palladium, iridium, ruthenium, osmium, and rhodium.

[0038] As used herein, “composite material” refers to a material having a combination of two or more different constituent materials, each of which retains its own unique properties but possesses properties that the constituent materials do not have when acting alone.

[0039] As used herein, “aliphatic” compounds are hydrocarbons that are saturated or unsaturated, acyclic or cyclic, unbranched or branched, unsubstituted or wholly or partially substituted with one or more substituents or functional groups. As will be understood by those skilled in the art, “aliphatic” herein is intended to include, but is not limited to, alkyl, alkenyl, and alkynyl moieties. Exemplary aliphatic groups include, but are not limited to, moieties such as 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.

[0040] As used herein, the term "alkyl" has its common meaning in the art and may include saturated aliphatic groups, including straight-chain alkyl, branched-chain alkyl, cycloalkyl (alicyclic) groups, alkyl-substituted cycloalkyl, and cycloalkyl-substituted alkyl groups. Similar convention applies to other general terms such as "alkenyl," "alkynyl," etc. Furthermore, as used herein, the terms "alkyl," "alkenyl," "alkynyl," etc., encompass both fully or partially substituted groups and unsubstituted groups.

[0041] In some embodiments, the straight-chain or branched alkyl chain may have 1 to 30 carbon atoms in its backbone, and in some cases may have 1 to 20 or fewer carbon atoms in its backbone. In some embodiments, the straight-chain or branched alkyl chain has 1 to 10 carbon atoms in its backbone (e.g., C1-C10 for straight chains, C3-C10 for branched chains), 6 or fewer carbon atoms, or 4 or fewer carbon atoms. Cycloalkyl groups 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 their ring structure. Examples of acyclic alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, n-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-undecyl, and dodecyl. Examples of cyclic alkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, and cyclohexyl.

[0042] The terms "alkenyl" and "alkynyl" refer to unsaturated aliphatic groups that are similar in length and possible substitutions to the alkyl groups described above, but each contains at least one double or triple bond. Alkenyl groups include, but are not limited to, vinyl, propenyl, butenyl, 1-methyl-2-buten-1-yl, etc. Non-limiting examples of alkynyl groups include ethynyl, 2-propynyl (propynyl), 1-propynyl, etc.

[0043] The term "heteroatom" refers to any atom other than carbon. Non-limiting examples of heteroatoms include B, N, O, Al, Si, P, S, Ge, As, Se, and Sb. In some instances, a heteroatom is an atom selected from B, N, O, P, and S.

[0044] The term "heteroalkyl" refers to an alkyl group in which one or more hydrogen atoms bonded to any carbon atom of the alkyl group, or one or more carbon atoms, are replaced by heteroatoms. Examples of heteroalkyl groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, methylthio, ethylthio, propylthio, isopropylthio, n-butylthio, methoxymethyl, and cyano.

[0045] The terms “heteroalkenyl” and “heteroynyl” refer to unsaturated aliphatic groups that are similar to the aforementioned heteroalkyl groups in length and possible substitutions, but respectively contain at least one double or triple bond.

[0046] The term "aryl" refers to an aromatic carbocyclic group and a heteroaryl group that is unsubstituted or fully or partially substituted, having a single ring (e.g., phenyl), multiple rings (e.g., biphenyl), or multiple fused rings, wherein at least one ring of the aryl group is aromatic (e.g., 1,2,3,4-tetrahydronaphthyl, naphthyl, anthraceneyl, or phenanthryl). That is, at least one ring of the aryl group has a conjugated π-electron system, while the other rings of the aryl group can be cycloalkyl, cycloalkenyl, cycloynyl, aryl, and / or heterocyclic. "Carbocyclic aryl" refers to an aryl group in which the ring atom on the aromatic ring is a carbon atom. Carbocyclic aryl groups include monocyclic carbocyclic aryl groups and polycyclic or fused compounds (e.g., two or more adjacent ring atoms shared by two adjacent rings), such as naphthyl. Aryl groups are not limited to benzene and its derivatives, but can have any suitable number of atoms in the ring. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, tetrahydronaphthyl, anilyl, indenyl, and indenyl.

[0047] The term "heteroaryl" refers to an aryl group (e.g., a heteroaromatic group) containing at least one heteroatom as a ring atom, such as a heterocyclic group. Non-limiting examples of heteroaryl groups include, but are not limited to, pyridyl, pyrazinyl, pyrimidinyl, pyrroleyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl, isoxazolyl, thiadiazolyl, oxadiazolyl, phenylthio, furanyl, quinolinyl, and isoquinolinyl. A heteroaryl group can be referred to as an A-heteroaryl group, where A is the element symbol for the heteroatom. For example, an N-heteroaryl group refers to an aryl group containing at least one nitrogen atom as a ring atom.

[0048] As used herein, the term "alkoxyl" or "alkoxy" refers to an alkyl group having an oxygen group attached thereto, and has the general formula R-O. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, and tert-butoxy.

[0049] The term "aryloxy group" refers to an aryl group having an oxygen group attached to it. Examples of aryloxy groups include, but are not limited to, phenoxy groups.

[0050] Any of the groups described above may optionally be completely or partially substituted. Examples of substituents include, but are not limited to: aliphatic groups, alicyclic groups, heteroaliphatic groups, heteroalicyclic groups, halogens, azides, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxy, amino, nitro, mercapto, imino, amide, phosphonate, hypophosphonate, carbonyl, carboxyl, alkoxycarbonyl, silyl, ether, alkylthio, heteroalkylthio, heteroarylthio, sulfonyl, sulfonamide, ketone, aldehyde, ester, heterocyclic, aromatic or heteroaromatic moiety, -CF3, -CN, aryl, aryloxy, perhaloalkoxy, arylalkoxy, heteroaryl, heteroaryloxy, heteroarylalkyl, heteroarylalkoxy, azide, amino. Amines, halides, alkylthio, oxo, acylalkyl, carboxyl esters, amides, acyloxy, aminoalkyl, alkylaminoaryl, alkylaryl, alkylaminoalkyl, alkoxyaryl, arylamino, aralkylamino, alkylsulfonyl, amidealkylaryl, amidealkylaryl, hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxyl-, aminoamidealkyl-, cyano, alkoxyalkyl, perhaloalkyl, arylalkyloxyalkyl (e.g., SO4(R')2), phosphate esters (e.g., PO4(R')3), silanes (e.g., Si(R')4), carbamates (e.g., R'O(CO)NH) R Furthermore, the substituents can 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 R appears each time x Independently including but not limited to hydrogen, aliphatic group, alicyclic group, heteroaliphatic group, heteroaliphatic group, aryl, heteroaryl, alkylaryl, or alkylheteroaryl, wherein any of the aliphatic group, alicyclic group, heteroaliphatic group, heteroaliphatic group, alkylaryl, or alkylheteroaryl substituents described above and herein may be substituted or unsubstituted, branched or unbranched, cyclic or acyclic, and wherein any of the aryl or heteroaryl substituents described above and herein may be substituted or unsubstituted.

[0051] Boric acid-functionalized carbon materials will now be described. Boric acid-functionalized carbon materials comprise carbon materials whose surfaces are functionalized with one or more boric acid groups. The boric acid groups can be linked to the carbon materials via ether or ester bonds. Any surface of the carbon material can be oxidized, including the outer surface and / or pore surfaces (e.g., the surface of the carbon material at the interface with pores within the carbon material).

[0052] Carbon materials are formed from hexagonal carbon rings with delocalized π electrons and include crystalline, semi-crystalline, subcrystalline, and amorphous carbon allotropes. Examples of carbon include, but are not limited to, carbon black, graphite, graphene, charcoal, activated carbon, soot, and coal, as well as carbon molecules (e.g., fullerenes and carbon nanotubes), and materials and structures formed from carbon molecules. Carbon black is a subcrystalline carbon material comprising randomly distributed primary graphite particles arranged in aggregates and / or agglomerates. Carbon black can exist in spherical, ellipsoidal, linear, or branched structures. Carbon black is highly porosimetric and conductive. The conductivity of carbon black increases with smaller and more spherical structures. Graphite is a crystalline allotropy of carbon arranged in multiple carbon layers. Each carbon atom within a layer is covalently bonded to three other carbon atoms in a hexagonal ring. Adjacent layers are bonded by weak van der Waals forces between the layers. Graphite is a material stable under redox conditions and exhibits high electrical conductivity. Graphene is a carbon material typically composed of 1 to 10 carbon layers. Each carbon atom within a layer is covalently bonded to three other carbon atoms in a hexagonal ring. Graphene is a material with very high electrical conductivity and high durability under redox conditions. Fullerenes are a class of molecules comprising a polyhedral cage composed entirely of n tricoordinated carbon atoms, having 12 pentagonal faces and (n / 2 – 10) hexagonal faces, where n ≥ 20. Examples of fullerenes include, but are not limited to, C 20 C 60 (buckminsterfullerene), C 70 C 72 C 76 C 84 and C 100Carbon nanotubes comprise hexagonal rings and include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Carbon materials can have any suitable shape, structure, and / or form, such as films, particles, spheres, ellipsoids, carbon powder, carbon cloth, nanofilms, nanotubes, nanobuds, nanoribbons, scaffolds, or nanofoams. Carbon materials also include composite materials of carbon materials with another material, such as polymers or ceramic materials. For example, carbon materials can include carbon-polymer composites, such as polymer matrices reinforced with carbon fibers or graphite particles. In some instances, carbon materials (e.g., graphite or nanotube structures) are porous due to interconnected voids or pores within the bulk of the carbon material.

[0053] Carbon materials can be oxidized to form oxidized carbon materials, wherein the surface of the carbon material is functionalized with oxide groups (e.g., but not limited to hydroxyl (OH), carbonyl (—C(=O)), carboxyl (—C(=O)OH), and epoxy groups (e.g., epoxide bridges between adjacent carbon atoms)). Oxidation of carbon black generates oxide groups on its graphite surface to add new physical and chemical properties while maintaining its electrical conductivity. Oxidation of graphite forms graphite oxide (GO) and adds oxide groups to the graphite surface to add new physical and chemical properties while maintaining its electrical conductivity. Graphene oxide (GrO) is a derivative of graphene containing oxide groups on its surface. Graphene oxide can be prepared from graphite oxide by exfoliating multilayer sheets of graphite oxide into single or few-atom-layer sheets (e.g., by chemical exfoliation). In some instances, chemical exfoliation involves dispersing graphite oxide in a polar solvent followed by ultrasonic treatment and / or mechanical stirring. Alternatively, graphene oxide can be prepared by the oxidation of graphene. The loading degree of oxide groups on the carbon material and the type of oxide groups added to the surface of the carbon material can be controlled by various oxidation processes to achieve desired physical, chemical, and / or electrical properties.

[0054] As explained in more detail herein, the oxide groups of oxidized carbon materials can be further covalently tethered to the boron moiety (e.g., boric acid or organoboronic acid) to form boric acid groups. For example, oxidized carbon materials can be functionalized with trivalent and / or tetravalent boric acid groups to form boric acid-functionalized carbon materials. Partial covalent modification of the oxide groups of oxidized carbon materials using nitrogen, sulfur, and / or phosphorus ligands can also be used to form nitrogen-containing, sulfur-containing, and / or phosphorus-containing functional groups (e.g., sulfonic acid and phosphonic acid functional groups), which may be suitable for their applications.

[0055] Figure 1 An illustrative reaction scheme for synthesizing oxidized carbon materials (e.g., carbon black oxide, graphite oxide, or graphene oxide) is shown. Figure 1 In this paper, a portion of a single layer (e.g., the outer surface layer) of a carbon material is shown as a representative starting material. It should be understood that carbon materials can have... Figure 1 Any other structure, shape, and size not shown, and any suitable carbon material may be used.

[0056] like Figure 1 As shown, carbon materials undergo an oxidation process to functionalize their surface with oxide groups. Any oxidation method suitable for carbon materials can be used, including "top-down" methods involving the use of strong oxidants, such as, but not limited to, the Brodie process, the Hummer process, and variations thereof. The Brodie process oxidizes carbon materials by treating them with a mixture of potassium chlorate (KClO3) and fuming nitric acid (HNO3). The Hummer process treats carbon materials with a mixture of sulfuric acid (H2SO4), sodium nitrate (NaNO3), and potassium permanganate (KMnO4). As an alternative to the "top-down" method of oxidizing carbon materials with oxidants, oxidized carbon materials can be synthesized using "bottom-up" methods, such as the Tang-Lau process and its variations. The Tang-Lau process uses glucose as the sole starting reagent in the self-assembly process and is described in Tang, L. et al. (2012). "Bottom-up synthesis of large-scalegraphene oxide nanosheets," Journal of Materials Chemistry, In 22 (12), 5676. Methods for synthesizing oxidized carbon materials (including the Brodie method, Hummer method, Tang-Lau method, and variations thereof) are known to those skilled in the art and will therefore not be described further.

[0057] Although Figure 1 The oxidized carbon materials exhibit six oxygen-containing functional groups (two hydroxyl groups, two carboxyl groups, and two epoxy groups), but the reaction chemistry can be controlled as needed to adjust the degree of oxidation and the type of oxide groups and / or the carbon-to-oxygen ratio (C:O) of the carbon materials. In some examples, the C:O ratio of the carbon materials ranges from 10:1 to 1:1, 9:1 to 1:1, 5:1 to 1:1, 4:1 to 1:1, 3:1 to 1:1, 5:1 to 2:1, 4:1 to 2:1, or 3:1 to 2:1.

[0058] The oxide groups on the surface of oxidized carbon materials can be used for boron bonding while maintaining the layered structure of the carbon material. As mentioned, boric acid-functionalized carbon materials comprise carbon material and boric acid groups bonded to the carbon material at its surface. In some instances, the boric acid groups are bonded to the carbon material (e.g., to carbon atoms in the carbon material's framework) via linkers (e.g., ether bonds, ester bonds, boronic acid linkers (e.g., derivatives of organoboronic acids), or polymeric boric acid linkers (e.g., derivatives of polymeric boric acids)). Boric acid groups include trivalent and tetravalent boric acid groups.

[0059] The trivalent borate group has a terminal borate group, wherein the boron atom participates in three covalent bonds and has at least one side-attached hydroxyl group. Examples of trivalent borate groups include, but are not limited to, —B(OH)₂, —B(OH)R, and —B(OH)(OR), wherein R is independently hydrogen, or a fully or partially substituted or unsubstituted alkyl or aryl group having 1 to 20, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms, such as, but not limited to, methyl, ethyl, propyl, or butyl. The trivalent borate group can be linked to a carbon material (e.g., to the carbon atoms of the carbon material skeleton) via an ether bond (—O—) or an ester bond (—C(=O)O—).

[0060] Trivalent boric acid-functionalized carbon materials can be used as catalyst supports. When used as catalyst supports in electrochemical applications (e.g., in catalyst layers / anodes / cathodes), trivalent boric acid-functionalized carbon materials offer enhanced catalytic performance compared to conventional carbon-based catalyst supports. For example, the terminal trivalent boric acid groups enhance conductivity and improve catalyst binding.

[0061] The tetravalent borate group has a terminal fluoroboric acid group, in which the boron atom is four-coordinated and covalently bonded to at least one fluorine atom. Boron typically has three valence electrons and a ground-state electronic configuration of 1s². 2 2s 2 2p 1 Boron forms a trivalent, trigonal neutral compound, in which boron passes through sp... 2 Hybridization results in three covalent bonds, such as boric acid (B(OH)3) and trivalent boric acid groups. 2 Hybridized boron atoms contain empty p orbitals, which makes trivalent boron compounds strongly electron-deficient, two electrons less electron-deficient than the stable octet electron configuration. Due to the empty p orbitals, boron is multivalent, allowing it to form negatively charged tetravalent compounds with four covalent bonds. Therefore, trivalent boron compounds (e.g., boric acids and organoboronic acids) are Lewis acids and readily accept electron pairs at the boron atom. Adding an anion (e.g., fluoride (e.g., through fluoride treatment), or other anions, results in an octet electron configuration, thus forming a highly stable negatively charged tetravalent tetrahedral boron compound with four covalent bonds. Tetravalent boron is also referred to herein as tetracoordinate boron. Examples of tetravalent borate groups include, but are not limited to, -BF3, -BF2R, -BF2(OR), and -BF(OH)2, wherein R is independently hydrogen, or a fully or partially substituted or unsubstituted alkyl or aryl group having 1 to 20, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms, such as, but not limited to, methyl, ethyl, propyl, or butyl. Tetravalent borate groups can be linked to carbon materials (e.g., carbon atoms of the carbon material) via ether bonds (-O-) or ester bonds (-C(=O)O-). Due to the tetracoordinate nature of the boron atom, tetravalent borate groups have a negative formal charge and can be connected to cations (e.g., but not limited to, H+). + Li + Na + Al 3 + Ni 2+ Balance (or any other suitable cation, including cations used in battery applications).

[0062] Tetravalent boric acid-functionalized carbon materials can be used as conductive ionomers. Oxygen-containing linkers provide hydrophilic domains near the hydrophobic carbon material framework, and the degree of functional modification can be used to tune the hydrophilic-lipophilic balance (HLB) of the carbon material. Furthermore, oxygen-containing linkers are suitable for electrochemical applications as ionomers and PEMs. Additionally, the ion exchange capacity of the modified carbon materials can be controlled and tuned as needed.

[0063] In some instances, boric acid-functionalized carbon materials contain both trivalent and tetravalent boric acid groups. In these examples, the modified carbon materials function as both a conductive catalyst support with enhanced catalyst bonding and a proton-conducting ionomer. Therefore, such modified carbon materials can be used in electrochemical cells (e.g., in catalyst and electrode layers).

[0064] Boric acid-functionalized carbon materials can be synthesized in any suitable manner. In some instances, trivalent boric acid-functionalized carbon materials are synthesized by combining boron compounds with oxidized carbon materials (e.g., carbon black oxide, graphite oxide, or graphene oxide) that have oxide groups on the surface of the carbon material. The boron compound reacts with the side-attached hydroxyl groups of the oxide groups in a condensation reaction to form trivalent boric acid groups linked to the carbon material via ether or ester bonds.

[0065] Boron compounds include, but are not limited to, boric acid (B(OH)3), organoboronic acids, organoboronic esters, or polyboronic acids. The general formula for organoboronic acids is B(OH)(R 1 (R) 2 ), where R 1 It is a hydroxyl, alkyl, and / or aryl (e.g., phenyl), and R 2 It is an alkyl and / or aryl group (e.g., phenyl). In some instances, R 1 and / or R 2 It has 1 to 20 carbon atoms. In other examples, R 1 and / or R 2 It has 1 to 10 carbon atoms. In another example, R 1 and / or R 2 They have 1 to 5 carbon atoms. The general formula for organoboroesters is B(OH)(R 3 (R) 4 ), where R 3 It is a hydroxyl, alkoxy, or aryloxy group, and R 4 It is an alkoxy or aryloxy group. In some instances, R... 3 and / or R 4 It has 1 to 10 carbon atoms. In other examples, R 3 and / or R 4 It has 1 to 5 carbon atoms. In another example, R 3 and / or R 4 It has 1 to 3 carbon atoms (e.g., methyl, ethyl, propyl, or isopropyl). Polyboronic acids are formed from boric acid monomers. For example, metaboric acid (Formula I) is a cyclic trimer of boric acid, and tetraboric acid (Formula II) is a bicyclic tetramer of boric acid. (I) and (II).

[0066] Polymerized metaboric acid is formed through further linear polymerization of metaboric acid units, and has the general formula HO[–B(BOH)2O3O–]. n H. Poly(tetraboronic acid) is also formed through further linear polymerization of tetraboronic acid units. Other polymeric boric acid structures are considered in this paper and can be used as boron compounds.

[0067] In some instances, tetravalent boric acid-functionalized carbon materials are synthesized by fluorinating trivalent boric acid-functionalized carbon materials to convert the trivalent boric acid groups into tetravalent boric acid groups. Fluorination treatment is performed using fluoroboronic acid groups with tetracoordinated boron atoms to functionalize the boric acid-functionalized carbon materials. Fluorination treatment can be carried out in any suitable manner.

[0068] In some instances, fluorination treatment involves combining a trivalent boric acid-functionalized carbon material with a fluoride reagent. In some instances, the fluoride reagent is hydrogen fluoride (HF). In other instances, the fluoride reagent is a metal fluoride. The metal in the metal fluoride can be any suitable metal, such as alkali metals (e.g., lithium (Li), sodium (Na), potassium (K)), alkaline earth metals (e.g., magnesium (Mg), calcium (Ca)), transition metals, or post-transition metals. Examples of metal fluorides include, but are not limited to, lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), potassium hydrogen fluoride (KHF2), and cesium fluoride (CsF). In other examples, the fluorinating agent is ammonium fluoride (NH4F), ammonium hydrogen fluoride (NH4F2), or tetraalkylammonium fluoride (general formula NR4F, wherein each R is independently hydrogen, or a fully or partially substituted or unsubstituted alkyl or aryl group having 1 to 20, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms, such as, but not limited to, methyl, ethyl, propyl, or butyl). In some examples, fluorination is performed using two or more different fluorinating agents (e.g., HF and NaF, HF and LiF, etc.).

[0069] Fluoride treatment adds a fluoride group to a side-mounted borate group to form a fluoroboronic acid group, in which the boron atom is tetracoordinated and covalently bonded to the fluoride group. Depending on the stoichiometry of the reaction, one or more hydroxyl groups of the borate group may also be replaced by fluoride ions from the fluoride reagent. Therefore, the side-mounted fluoroboronic acid group has a negative charge and is formed by cations (e.g., H+). + Li + Na + K + Cs + NH4+ or NR4 + )balance.

[0070] In some instances where the countercation is not hydrogen (e.g., when the fluoride compound is one or more of LiF, NaF, KF, KHF2, CsF, NH4F, NH4F2, or NR4F), the fluoride treatment may be followed by a protonation step to use protons (H+). + The protonation step can be performed in any suitable manner, replacing the countercation. In some instances, the protonation step is carried out by combining a fluoroboric acid-functionalized carbon material with a strong acid. Examples of suitable strong acids include, but are not limited to, hydrochloric acid (HCl), sulfuric acid (H₂SO₄), methanesulfonic acid (CH₃SO₃H), and trifluoroacetic acid (CF₃CO₂H). After the protonation step, the side-attached fluoroboric acid group is formed by a proton (H₂O). + )balance.

[0071] In other examples of fluorination treatment, one or more hydrogen atoms of the hydroxyl groups of the trivalent boric acid side-mounted group are replaced by fluoroboronic acid groups. In these examples, fluorination treatment involves functionalizing trivalent boric acid in carbon materials with the formula BF... m (OH) (3-m) Fluoroboric acid compounds (where m is 1, 2, or 3) (e.g., fluorodihydroxyboronic acid (BF(OH)2), difluorohydroxyboronic acid (BF2(OH)), and / or boron trifluoride (BF3)). In another example, the fluoride treatment also includes in situ merging of trivalent boric acid-functionalized carbon material with organoboric acid and fluoride reagent (e.g., HF) in a one-pot process, wherein the fluoride reagent is used as a limiting reagent, and R is a branched or unbranched, fully or partially substituted or unsubstituted alkyl or aryl group (e.g., 1 to 20, 1 to 10, 1 to 8, 1 to 6, 1 to 4, or 1 to 3 carbon atoms).

[0072] In instances where the reaction produces a tetracoordinated borate group having one or two remaining hydroxyl groups, the same reaction can be repeated, or different reactions can be carried out to replace one or both of the remaining hydroxyl groups with a fluorine group or other anion (e.g., a halogen).

[0073] It should be recognized that other fluoride treatments are possible and can be used. Fluoride treatments produce carbon materials that are functionalized by one or more tetravalent boric acid groups attached to the surface of the carbon material. Illustrative examples of boric acid-functionalized carbon materials and methods for preparing boric acid-functionalized carbon materials will now be described.

[0074] Figure 2An illustrative reaction scheme for synthesizing boric acid-functionalized carbon materials with trivalent boric acid groups on the surface of the carbon material is shown. Boric acid molecules react with hydroxyl groups to generate trivalent boric acid groups of the general formula -OB(OH)2. Boric acid molecules also react with carboxyl groups to generate trivalent boric acid groups of the general formula -C(=O)OB(OH)2. Boric acid molecules also react with epoxy groups to generate trivalent boric acid groups of the general formula -OB(OH)2. The reaction with epoxy groups also generates another hydroxyl group on the surface of the carbon material, which, as described herein, can also react with boric acid molecules depending on the stoichiometry of the reaction and the desired boric acid group loading. The reaction can be controlled... Figure 2 The reaction scheme was designed to achieve the desired loading of trivalent boric acid groups. Through... Figure 2 The boric acid-functionalized carbon materials produced by the reaction scheme can be used as conductive catalyst solid supports with enhanced catalyst binding.

[0075] Figure 3 Another illustrative reaction scheme for synthesizing boric acid-functionalized carbon materials having both trivalent and tetravalent boric acid groups is shown. In the first reaction step, ... Figure 1 The oxidized carbon material produced in the method is combined with boric acid (B(OH)3) to produce a boric acid-functionalized carbon material with trivalent boric acid groups (e.g., by performing...). Figure 2 (Reaction scheme). In the second reaction step, a fluorination treatment is performed to convert at least some of the trivalent borate groups into tetravalent borate groups. Figure 3 In some examples, fluorination treatment involves combining trivalent boric acid-functionalized carbon material with potassium hydrogen fluoride (KHF2) and / or hydrogen fluoride (HF) to form tetravalent boric acid groups (e.g., boron trifluoride groups (—BF3)). The boron atom in the tetravalent boric acid group is covalently bonded to three fluorine atoms and covalently bonded to the carbon atoms of the carbon material skeleton via ester bonds. The tetravalent boric acid groups have a negative formal charge, making these boric acid group atoms inherently acidic and ionic. Therefore, tetravalent boric acid groups can be used as cation exchange groups (e.g., proton transporters).

[0076] exist Figure 3 In the example shown, the boric acid-functionalized carbon material produced in the second step contains both trivalent and tetravalent boric acid groups. The loading of trivalent and tetravalent boric acid groups can be adjusted as needed. In some examples, all or substantially all (e.g., greater than 90%, 95%, 98%, or 99%) of the trivalent boric acid groups are converted to tetravalent boric acid groups.

[0077] pass Figure 3The reaction scheme produces boric acid-functionalized carbon materials containing both trivalent and tetravalent boric acid groups, and therefore can be used as multifunctional (all-in-one) materials: conductive solid supports, catalyst binders with enhanced performance via boron, and cationic conductive ionomers. Fluoride reagents (e.g., KHF2 or HF) can be used as limiting agents to optimize or adjust the ion exchange capacity (IEC) of the boric acid-functionalized carbon materials as needed.

[0078] Figure 4 Another illustrative reaction scheme for the one-pot synthesis of boric acid-functionalized carbon materials with tetravalent boric acid groups is shown. Figure 4 In the reaction scheme, Figure 1 The oxidized carbon material produced in the method combines with a boron compound (e.g., boric acid) and a fluoride reagent (e.g., KHF₂) and HCl, which react with the oxide groups of the oxygen-containing carbon material to form tetravalent borate groups (e.g., tetravalent boron trifluoride groups). The tetravalent boron atoms have a negative formal charge, making them inherently acidic and ionic. Therefore, the tetravalent borate groups can be used as ion-exchange groups (e.g., proton transporters).

[0079] pass Figure 4 The boric acid-functionalized carbon materials produced by this reaction scheme can be used as dual-purpose conductive solid supports and proton-conducting ionomers. The ion exchange capacity (IEC) of the boric acid-functionalized carbon materials can be adjusted or optimized by controlled boron loading.

[0080] Various modifications can be made to the above materials and reaction scheme. As mentioned above, organoboronic acids, organoboroesters, and / or polymeric boric acids can be used instead of boric acid. Polymeric boric acids can modify the surface properties of carbon materials through boron crosslinking. In some examples, the boric acid groups are further linked to the carbon skeleton of the carbon material via linkers. The linkers can be C1 to C2. 30 An alkyl linker chain, and optionally having one or more side-mounted portions, which may be the same or different, and may each be independently selected from hydrogen, hydroxyl, fluorine, chlorine, dialkylamino, cyano, carboxylic acid, carboxamide, ester, alkyl, alkoxy, and aryl. In some examples, Figure 1 The oxidizing agent used in the reaction scheme includes a linker. In another example, the boron compound reacting with the oxide group includes a linker. For example, the linker may be an organoboronic acid linker (e.g., a derivative of an organoboronic acid) or a polymeroboronic acid linker (e.g., a derivative of a polymeroboronic acid).

[0081] In another example, the tetravalent borate group of borate-functionalized carbon materials can react with any other cation other than a proton (e.g., but not limited to H+).+ Li + Na + K + Cs + NH4 + or NR4 + Ionic bonding.

[0082] Compared to conventional materials and methods for preparing conventional materials, boric acid-functionalized carbon materials and methods for preparing boric acid-functionalized carbon materials offer various benefits and advantages. The reaction schemes described herein are applicable to any standard carbon material, including commercially available carbon materials such as carbon powder, carbon cloth, Vulcan XC 72, and carbon-polymer composite films. The reagents in the reaction schemes are easy to handle, and the reaction schemes are easily scalable. Furthermore, the reagents are typically common and inexpensive materials, thus providing a cost reduction compared to conventional materials used in electrochemical cells.

[0083] Furthermore, oxygen-containing linkers (which attach boric acid groups to the carbon skeleton of boric acid-functionalized carbon materials) provide hydrophilic domains within the hydrophobic carbon skeleton and can tune the hydrophilic-lipophilic balance (HLB). Additionally, oxygen-containing linkers are suitable for electrochemical applications as ionomers and PEMs (e.g., polyfluorosulfonic acid (PFSA) PEMs (e.g., Nafion and Aquivion)). The ion exchange capacity (IEC) of boric acid-functionalized carbon materials can be controlled and tuned to obtain desired or optimized performance and anticipated functional applications.

[0084] Oxygen-containing trivalent boric acid groups are ideal catalyst supports for enhancing catalyst performance. Furthermore, tetravalent boric acid groups are inherently ionic and acidic, and therefore can be used as cation exchangers.

[0085] The boric acid-functionalized carbon materials described herein can be used in electrochemical systems (e.g., water electrolysis systems and fuel cell systems). For example, the boric acid-functionalized carbon materials described herein can be used as carbon-based solid supports for catalysts. Additionally or alternatively, the boric acid-functionalized carbon materials can be used in porous transport layers / gas diffusion layers (GDLs) (e.g., as gas diffusion electrodes) in water electrolysis systems and fuel cell systems. The boric acid-functionalized carbon materials described herein are believed to reduce the dissociation of carbon materials under strong redox conditions, thereby enabling the use of carbon-based GDLs at the anode of electrochemical cells to replace titanium-based porous transport layers. In some instances, the gas diffusion electrode can be directly modified according to any of the reaction schemes described above.

[0086] Figure 5An exemplary proton exchange membrane water electrolysis system 500 (PEM water electrolysis system 500) is shown. The PEM water electrolysis system 500 uses electricity to decompose water into oxygen (O2) and hydrogen (H2) via an electrochemical reaction. The configuration of the PEM water electrolysis system 500 is exemplary and not limiting.

[0087] like Figure 5 As shown, the PEM water electrolysis system 500 includes a membrane electrode assembly 502 (MEA 502), porous transport layers 504-1 and 504-2 (e.g., a gas diffusion layer), bipolar plates 506-1 and 506-2, and a power supply 508. The PEM water electrolysis system 500 may also include... Figure 5 Additional or alternative components, not shown, that may be used in a particular implementation.

[0088] MEA 502 includes a PEM 510 located between a first catalyst layer 512-1 and a second catalyst layer 512-2. The PEM 510 electrically isolates the first catalyst layer 512-1 from the second catalyst layer 512-2 while providing cations (e.g., protons (H+)). ＋ PEM 510 exhibits selective conductivity and is simultaneously impermeable to gases (e.g., hydrogen and oxygen). It can be achieved from any suitable organic or inorganic PEM. Illustrative examples of organic PEMs include, but are not limited to, synthetic and natural polymers. Examples of synthetic polymers include sulfonate-functionalized polymers, such as Nafion. ® (Available in various configurations and grades from EIDupont de Nemours and Company, including Nafion-H, Nafion HP, Nafion 117, Nafion 115, Nafion 212, Nafion 211, Nafion NE1035, Nafion XL, etc.), Aquivion ® (Available in various configurations and grades from Solvay SA, including Aquivion® E98-05, Aquivion® PW98, Aquivion® PW87S, etc.), Gore-Select ® (Available from WL Gore & Associates, Inc.), Flemion TM (Available from Asahi Glass Company), Pemion+ TM(Available from Ionomr Innovations, Inc.), and any combination, derivative, grade, or configuration thereof. Examples of natural polymers include, but are not limited to, lignin, cellulose, or chitin. Examples of inorganic PEMs include, but are not limited to, amorphous inorganic materials (e.g., glass, fused silica, or ceramics) and / or crystalline inorganic materials (e.g., quartz, monocrystalline silicon, or alumina).

[0089] The first catalyst layer 512-1 and the second catalyst layer 512-2 are conductive electrodes, each comprising a solid catalyst support bonded to electrocatalyst particles (not shown), such as platinum group metals, metal alloys, and / or metal oxides. In some instances, the catalyst particles are supported on a catalyst support formed from boric acid-functionalized carbon materials as described herein.

[0090] In some instances, the first catalyst layer 712-1 and / or the second catalyst layer 712-2 comprises a supported catalyst mixed with an ionomer (an ion-conducting polymer). The ionomer binds the catalyst within the electrode, binds to the catalyst layer on the PEM, and provides a pathway for cations (e.g., protons), thereby improving cation conductivity. The ionomer used in the first catalyst layer 712-1 and the second catalyst layer 712-2 may include any suitable ionomer (including any ionomer described herein).

[0091] In some instances, the first catalyst layer 512-1 and / or the second catalyst layer 512-2 comprise conductive boric acid-functionalized carbon materials containing trivalent and tetravalent boric acid groups as described herein. Thus, the boric acid-functionalized carbon materials serve as catalyst supports, catalyst binders, and proton-conducting ionomers.

[0092] MEA 502 is placed between porous transport layers 504-1 and 504-2, which are then placed between bipolar plates 506-1 and 506-2, wherein flow channels 514-1 and 514-2 are located between bipolar plate 506 and porous transport layer 504. In some examples, porous transport layers 504-1 and / or 504-2 comprise conductive boric acid-functionalized carbon materials containing trivalent and / or tetravalent boric acid groups as described herein.

[0093] In MEA 502, the first catalyst layer 512-1 acts as the anode, and the second catalyst layer 512-2 acts as the cathode. When the PEM water electrolysis system 500 is powered by the power supply 508, an oxygen evolution reaction (OER) occurs at the first catalyst layer / anode 512-1. The OER is promoted by the electrocatalyst bonded to the solid catalyst support in the first catalyst layer / anode 512-1. The OER is represented by the following electrochemical half-reaction: (1).

[0094] Protons travel from the first catalyst layer / anode 512-1 through PEM 510 to the second catalyst layer / cathode 512-2, while electrons bypass PEM 510 and travel from the first catalyst layer / anode 512-1 to the second catalyst layer / cathode 512-2 via a conduction path. PEM 510 allows protons (H... + Water and oxygen are transported from the first catalyst layer / anode 512-1 to the second catalyst layer / cathode 512-2, but oxygen and hydrogen are impermeable. At the second catalyst layer / cathode 512-2, protons combine with electrons in the hydrogen evolution reaction (HER), which is promoted by an electrocatalyst bonded to a solid catalyst support in the second catalyst layer / cathode 512-2. HER is represented by the following electrochemical half-reaction: (2).

[0095] OER and HER are two complementary electrochemical reactions used to split water by electrolysis, which is represented by the following total water electrolysis reaction: (3).

[0096] Figure 6 An exemplary proton exchange membrane fuel cell 600 (PEM fuel cell 600) is shown. The PEM fuel cell 600 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 600 is merely exemplary and not limiting.

[0097] like Figure 6 As shown, the PEM fuel cell 600 includes a membrane electrode assembly 602 (MEA 602), porous transport layers 604-1 and 604-2 (e.g., a gas diffusion layer), bipolar plates 606-1 and 606-2. An electrical load 608 can be electrically connected to the MEA 602 and driven by the PEM fuel cell 600. The PEM fuel cell 600 may also include... Figure 6 Additional or alternative components, not shown, that may be used in a particular implementation.

[0098] MEA 602 includes a PEM 610 located between a first catalyst layer 612-1 and a second catalyst layer 612-2. The PEM 610 electrically isolates the first catalyst layer 612-1 from the second catalyst layer 612-2 while providing cations (e.g., protons (H+)). ＋ It exhibits selective conductivity and is simultaneously impermeable to gases (e.g., hydrogen and oxygen). PEM 610 can be achieved by any suitable PEM described herein (including any PEM described herein).

[0099] The first catalyst layer 612-1 and the second catalyst layer 612-2 are conductive electrodes comprising a catalyst solid support incorporating electrocatalyst particles (not shown), such as platinum metal, metal alloys, and / or metal oxides. In some instances, the catalyst particles are supported on a catalyst support formed from boric acid-functionalized carbon materials as described herein.

[0100] In some instances, the first catalyst layer 612-1 and / or the second catalyst layer 612-2 comprises a supported catalyst mixed with an ionomer (an ion-conducting polymer). The ionomer binds the catalyst within the electrode, binds to the catalyst layer on the PEM, and provides a pathway for cations (e.g., protons), thereby improving cation conductivity. The ionomer used in the first catalyst layer 612-1 and the second catalyst layer 612-2 may include any suitable ionomer (including any ionomer described herein).

[0101] In some instances, the first catalyst layer 612-1 and / or the second catalyst layer 612-2 comprise conductive boric acid-functionalized carbon materials containing trivalent and tetravalent boric acid groups as described herein. Thus, the boric acid-functionalized carbon materials serve as catalyst supports, catalyst binders, and proton-conducting ionomers.

[0102] MEA 602 is placed between porous transport layers 604-1 and 604-2, which are further placed between bipolar plates 606-1 and 606-2, with flow channels 614 located therebetween. In some instances, porous transport layers 564-1 and / or 604-2 comprise conductive boric acid-functionalized carbon materials containing trivalent and / or tetravalent boric acid groups as described herein.

[0103] In MEA 602, the first catalyst layer 612-1 acts as the cathode, and the second catalyst layer 612-2 acts as the anode. The first catalyst layer / cathode 612-1 and the second catalyst layer / anode 612-2 are electrically connected to the load 608, and the load 608 is electrically driven by the PEM fuel cell 600.

[0104] During operation of the PEM fuel cell 600, hydrogen (H2) flows into the anode side of the PEM fuel cell 600, while oxygen (O2) flows into the cathode side of the PEM fuel cell 600. At the second catalyst layer / anode 612-2, hydrogen molecules are catalytically decomposed into protons (H2) according to the following hydrogen oxidation reaction (HOR). + ) and electrons (e - The hydrogenation reaction (HOR) is promoted by electrocatalyst particles bonded to the solid catalyst support in the second catalyst layer / anode 612-2: (4).

[0105] Protons travel from anode 612-2 through PEM 610 to the first catalyst layer / cathode 612-1, while electrons bypass PEM 610 and travel from the second catalyst layer / anode 612-2 through the conduction path and load 608 to the first catalyst layer / cathode 612-1. At the first catalyst layer / cathode 612-1, protons and electrons combine with oxygen according to the oxygen reduction reaction (ORR), which is promoted by the electrochemical catalyst particles bound to the catalyst solid support in the first catalyst layer / anode 612-1: (5).

[0106] Therefore, the overall electrochemical reaction of the PEM fuel cell 600 is: (6).

[0107] In the overall reaction, the PEM fuel cell 600 produces water at the first catalyst layer / cathode 612-1. The water can flow from the first catalyst layer / cathode 612-1 through the PEM 610 to the second catalyst layer / anode 612-2, and can be removed through outlets at the cathode side and / or anode side of the PEM fuel cell 600. The overall reaction generates electrons at the anode to drive the load 608.

[0108] exist Figure 5 and Figure 6 In the examples, MEA 502 and MEA 602 include a catalyst layer 512 / 612 formed on PEM 510 / 610. In alternative configurations, the catalyst layer 512 / 612 can be coated onto PEM 510 / 610 to form a catalyst-coated membrane (CCM). For example, the catalyst layer 512 / 612 can be formed in a one-pot or staged manner and sprayed onto PEM 510 / 610.

[0109] This article has described boric acid-functionalized carbon materials for electrochemical battery applications (e.g., water electrolysis and hydrogen fuel cell applications). However, boric acid-functionalized carbon materials can also be used for other applications. For example, the pKa of boric acid-functionalized carbon materials can be controlled to a level desired for many applications, including electrochemical processes for ammonia production.

[0110] In some instances, boric acid-functionalized carbon materials can be used in batteries, flow batteries, and / or in the synthesis of ammonia. For example, boric acid-functionalized carbon materials with tetravalent boric acid groups can be used in graphite electrodes for lithium-ion batteries.

[0111] In the foregoing description, various exemplary embodiments have been described with reference to the accompanying drawings. However, it will be apparent that various modifications and alterations can be made thereto, and additional embodiments can be implemented, without departing from the scope of the appended claims. For example, certain features of one embodiment described herein may be combined or substituted with features of another embodiment described herein. Therefore, the specification and drawings should be considered exemplary and not restrictive.

Claims

1. A boric acid-functionalized carbon material, wherein the boric acid-functionalized carbon material comprises: Carbon materials; and Boric acid groups attached to the surface of the carbon material.

2. The boric acid-functionalized carbon material according to claim 1, wherein the carbon material comprises carbon black, graphite, or graphene.

3. The boric acid-functionalized carbon material according to claim 1, wherein the carbon material includes charcoal, activated carbon, soot, or coal.

4. The boric acid-functionalized carbon material according to claim 1, wherein the carbon material comprises fullerene or carbon nanotubes.

5. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid group includes a trivalent boric acid group.

6. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid group has the general formula —B(OH)2.

7. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid group comprises a tetravalent boric acid group.

8. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid group includes a fluoroboronic acid group.

9. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid group comprises a combination of trivalent boric acid groups and tetravalent boric acid groups.

10. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid groups are connected to the surface of the carbon material via ether bonds.

11. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid groups are connected to the surface of the carbon material via ester bonds.

12. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid groups are connected to the surface of the carbon material via an organoboric acid linker or a polymeric boric acid linker.

13. The boric acid-functionalized carbon material according to claim 1, wherein the surface of the carbon material includes the surface of the carbon material at the interface with the pores within the carbon material.

14. The boric acid-functionalized carbon material according to claim 1, wherein the boric acid-functionalized carbon material further comprises a cation ionicly linked to the boric acid group.

15. A method for preparing boric acid-functionalized carbon materials, the method comprising: Oxidized carbon material is reacted with a boron compound to form a trivalent boric acid-functionalized carbon material, the trivalent boric acid-functionalized carbon material comprising trivalent boric acid groups attached to the surface of the carbon material.

16. The method of claim 15, wherein the oxidized carbon material comprises carbon black oxide.

17. The method of claim 15, wherein the oxidized carbon material comprises graphite oxide or graphene oxide.

18. The method of claim 15, wherein the boron compound comprises boric acid.

19. The method of claim 15, wherein the boron compound comprises the general formula B(OH)(R 1 (R) 2 Organic boric acids, wherein R 1 It is hydroxyl, alkyl and / or aryl, and R 2 It is an alkyl and / or aryl group.

20. The method of claim 15, wherein the boron compound comprises the general formula B(OH)(R 3 (R) 4 Organic borate esters, wherein R 3 It is a hydroxyl, alkoxy, or aryl group, and R 4 It is an alkoxy or aryloxy group.

21. The method of claim 15, wherein the boron compound comprises polymeric boric acid.

22. The method of claim 21, wherein the polymeric boric acid comprises polymeric metaboric acid.

23. The method of claim 21, wherein the polymeric boric acid comprises polymeric tetraboric acid.

24. The method of claim 15, further comprising subjecting the trivalent boric acid-functionalized carbon material to a fluoride treatment to convert the trivalent boric acid groups into tetravalent boric acid groups.

25. The method of claim 24, wherein the fluoride treatment comprises: The trivalent boric acid groups of the boric acid-functionalized carbon material are reacted with a fluoride reagent.

26. The method of claim 25, wherein the fluoride reagent comprises hydrogen fluoride (HF), lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), potassium hydrogen fluoride (KHF2), cesium fluoride (CsF), ammonium fluoride (NH4F), ammonium hydrogen fluoride (NH4F2), or tetraalkylammonium fluoride of the general formula NR4F, wherein each R is independently hydrogen, or a substituted or unsubstituted alkyl or aryl group.

27. The method of claim 25, wherein the fluoride reagent comprises boron trifluoride.

28. The method of claim 24, wherein the reaction of the oxidized carbon material with the boron compound and the fluoride treatment are carried out in a one-pot process.

29. A catalyst support, said catalyst support comprising: Carbon materials; and Boric acid groups attached to the surface of the carbon material.

30. A gas diffusion layer for an electrochemical cell, the gas diffusion layer comprising: Carbon materials; and Boric acid groups attached to the surface of the carbon material.

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