Composite material for fuel cells, process of preparation and applications thereof

Abstract

The present invention generally relates to fuel cells, specifically Proton Exchange Membrane Fuel Cell (PEMFC). The present invention relates to a composite material for coating electrode(s) or membrane in fuel cells comprising M1 metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon; and a process of preparation thereof. Further, the present invention relates to a composition for fuel cells comprising effective amount or ratio of polymer based solid electrolyte and the composite material. The invention also relates to half PEM fuel cell and / or full PEM fuel cell comprising said composite material as coating layer onto electrode or membrane placed over / in between electrode(s).

Description

[0001] COMPOSITE MATERIAL FOR FUEL CELLS, PROCESS OF PREPARATION AND APPLICATIONS THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to fuel cells, specifically the Proton Exchange Membrane Fuel Cell (PEMFC). The present invention relates to a composite material for coating electrode(s) or membrane placed between electrodes in fuel cells, comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon; and a process of preparation thereof. Further, the present invention relates to a composition for fuel cells comprising an effective amount or ratio of polymer based solid electrolyte (also can be termed as ionomer) and the composite material. The invention also relates to half PEM fuel cell and / or full PEM fuel cell comprising said composite material.

[0004] BACKGROUND AND PRIOR ART OF THE INVENTION

[0005] Polymer electrolyte membrane fuel cells (PEMFCs) have garnered significant attention as a potential solution to address energy and environmental challenges. They represent the most promising energy conversion devices for various applications, including automotive, stationary, and portable systems. This is primarily due to their advantageous characteristics such as zero emissions, rapid start-up, and high-energy density achieved at low operating temperatures. However, the widespread commercialization of PEMFCs faces obstacles in the form of high costs and limited material durability. Two predominant challenges arise from the sluggish kinetics of the fuel cells are oxygen reduction reaction (ORR) and mass transport restrictions at high current densities caused by the liquid water. Efficient removal of water from the cathode side of the fuel cell is often problematic, resulting in compromised oxygen transfer to the cathode electrode's reaction sites.

[0006] So far, platinum and its alloys have stood as widely employed benchmark electrocatalysts for PEMFCs, owing to their exceptional advantages, including favourable output voltage, reactivity at low temperatures, and low electrochemical overpotential. However, there are various obstacles associated with platinum electrocatalysts, such as their high cost, limited availability, short lifespan, and sluggish electron transfer kinetics. To address these challenges, it is crucial to adopt a practical strategy for creating efficient electrocatalysts that have minimal loading and maximal utilization. The impact of catalyst nanoparticle size, shape, and distribution on the support materials is widely acknowledged to significantly influence the performance of the fuel cell.

[0007] Furthermore, catalyst support materials play a crucial role in regulating various properties, including providing a large specific surface area, facilitating rapid electron transfer during reactions through superior electrical conductivity, ensuring excellent electrochemical stability in challenging operating conditions, and effectively immobilizing the catalyst to enhance the triple phase boundaries in the fuel cell electrodes. Pt nanoparticle supported on carbon black (Pt / C) is considered as the state-of-the-art electrocatalyst for ORR occurring at the cathode (refer, Ashkan Koushanpour et al., ACS Appl. Mater. Interfaces 2022, 14, 17, pages 19285-19294). Nevertheless, the PEMFC’s efficiency declines as a consequence of the electrochemical oxidation of the supporting material, leading to catalyst detachment and simultaneous agglomeration, which restricts its real-world usage. Also, said Pt / C suffers from other disadvantages or limitations like low surface area, not efficient gas / H2 / O2flow, and flooding which causes lower electrochemical reaction and analysis along with longer activation time required, and lesser stability of material towards electrochemical condition.

[0008] Additionally, one of the articles Karthikeyan K. Karuppanan et al., J. Mater. Chem. A, 6, pages 12768-12781, 12-June-2018, reports Pt-grafted, hierarchical mesoporous carbon nanofibers (Pt / MPCNFs) electrocatalysts have been developed using electrospinning for high-performance PEM fuel cells. However, the power output achieved with this material is significantly lower when compared to the other materials, which demonstrated a twofold increase in power output. Moreover, the conventionally produced PEMFC electrodes (e.g. as provided in Saijun Wang et al., Applied Catalysis B: Environmental, Volume 298, 5 December 2021, 120512, Pages 1-11; and Yu Wang et al., Applied Surface Science, Volume 604, 1 December 2022, 154475) typically have problems with water dissipation, mass transfer, charge transfer, and catalyst utilization. Collectively, these have a considerable negative impact on the fuel cell's performance, especially when used in Hi-Air environments. It is critical to design a strategy that would tackle all of these significant challenges in a more controlled manner.

[0009] Hence, there is a need of an electrocatalyst material which can be coated onto an electrode or membrane coated with placed in between electrodes in fuel cells, and which will have better or improved effects in terms of water dissipation, mass transfer, charge transfer, and catalyst utilization. These problems are well addressed by the inventors of the present invention by providing new and effective composite material for coating electrode(s) or membrane in fuel cells comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon.

[0010] OBJECTIVES OF THE INVENTION

[0011] An objective of the present invention is to provide a composite material for coating electrode(s) or membrane of fuel cells, the composite material comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon.

[0012] Another objective of the present invention is to provide a process of preparation of said composite material comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon.

[0013] Another objective of the present invention is to provide a composition for fuel cells comprising an effective amount or ratio of polymer based solid electrolyte and the composite material, wherein said polymer based solid electrolytes act as proton exchange material.

[0014] Yet another objective of the present invention is to provide a half PEM fuel cell comprising said composite material as a coating layer onto electrode(s) or membrane placed over / in between electrode(s).

[0015] Still, another objective of the present invention is to provide a full PEM fuel cell comprising said composite material as a coating layer onto electrode(s) or membrane placed over / in between electrode(s).

[0016] SUMMARY OF THE INVENTION

[0017] In an aspect, the present invention provides a composite material for coating electrode(s) or membrane of fuel cells, the composite material comprising: i. Ml metal nanoparticles, and ii. nitrogen doped 3D graphitic carbon; wherein the Ml metal nanoparticles are dispersed or anchored over said nitrogen doped 3D graphitic carbon; and wherein the metal of said Ml metal nanoparticles is selected from a noble metal, alloy of noble metals, and alloy of noble metal and transition metal. In an embodiment, the noble metal is selected from platinum, palladium, silver, ruthenium, rhodium, and iridium.

[0018] In an embodiment, the transition metal is selected from cobalt, nickel, tin, manganese, copper, and tungsten.

[0019] In an embodiment, the surface area of the composite material is in the range of around 950 to 1000 m2 / g.

[0020] In an embodiment, the composite material is microporous in nature with microporosity below 2 nm or in the range of 0.2 to 2 nm.

[0021] In an embodiment, the particle size of the Ml metal nanoparticles is in the range of 0.5 to 10 nm.

[0022] In an embodiment, the pore volume of the composite material is in the range of 0.5 to 0.9 cc / g.

[0023] In another aspect, the present invention provides a process of preparation of composite material, the process comprising steps of: i) preparing oxidative polymerized intermediate by reacting melamine sponge or polyurethane sponge with polydopamine or catechol containing polymer in the presence of buffer at temperature in the range of 20-40 °C for a time period of 20 to 28 h to form the oxidative polymerized intermediate; ii) annealing the intermediate of i) at a temperature in the range of 800 to 1000 °C for a time period in the range of 2 to 4 h under an inert atmosphere to obtain an annealed product of nitrogen doped 3D carbon; and iii) decorating or anchoring Ml metal nanoparticles onto said annealed product of nitrogen doped 3D carbon of ii) by reacting Ml metal precursor with said annealed product of ii) in the presence of polyol or mixture of polyol and water at a temperature in the range of 110 to 150 °C for a time period in the range of 5 to 7.5 h to obtain the composite material.

[0024] In an embodiment, the metal in said Ml metal precursor is selected from noble metal, alloy of noble metals, and alloy of noble metal and transition metal.

[0025] In an embodiment, the noble metal is selected from platinum, palladium, silver, ruthenium, rhodium, and iridium. In an embodiment, the transition metal is selected from cobalt, nickel, tin, manganese, copper and tungsten.

[0026] In an embodiment, the Ml metal precursor is selected from chloroplatinic acid, potassium hexachloroplatinate, platinum(II) acetylacetonate, palladium(II) nitrate, palladium(II) chloride, tetraamminepalladium(II) chloride monohydrate, nickel(II) chloride, nickel(II) nitrate, nickel(II) acetylacetonate, cobalt(II) acetylacetonate, cobalt(II) nitrate hexahydrate, cobalt(II) chloride and combinations thereof.

[0027] In an embodiment, the polyol is selected from ethylene glycol, propylene glycol (PG), glycerol, diethylene glycol (DEG), triethylene glycol (TEG), 1,2 -butanediol and combinations thereof.

[0028] In an embodiment, the buffer used in step i) is selected from bicarbonate buffer, tris-HCl Buffer (Tris(hydroxymethyl)aminomethane), Bicine (N,N-Bis(2-hydroxyethyl)glycine), Glycine-NaOH Buffer and combinations thereof.

[0029] In an embodiment, prior to iii), the process comprises acid-washing of an annealed product of nitrogen doped 3D carbon of ii) with 0.5 M of acid H2SO4at a temperature in the range of 60 to 100 °C for a time period in the range of 3 to 5 h, followed by at least three times washing with deionized (DI) water and subsequent drying.

[0030] In another aspect, the present invention provides a composition for fuel cells, comprising: an effective amount or ratio of polymer based solid electrolyte and the composite material, wherein said polymer based solid electrolyte act as proton exchange material; and wherein the ratio of polymer based solid electrolyte and the graphitic carbon of the composite material is in range of 0.4 to 0.8.

[0031] In an embodiment, the polymer based solid electrolyte is in aqueous solution form and is selected from nafion, polybenzimidazole (PBI), sulfonated polyether ether ketone (SPEEK), poly(arylene ether sulfone) (PAES), poly(phenylene oxide) (PPG), and polyimide (PI).

[0032] In an embodiment, the aqueous solution of polymer based solid electrolyte is in concentration ranging between 5 to 20% w / v.

[0033] In another aspect, the present invention provides a half PEM fuel cell comprising: a) working electrode, b) the counter electrode, c) reference electrode, d) proton exchange membrane, e) electrolyte, and f) the composite material, wherein the composite material is present in the fuel cell as coating layer onto said working electrode or as a membrane placed over / in between electrodes of a), b) or c).

[0034] In an embodiment, the working electrode is selected from a carbon electrode, glassy carbon electrode, gas diffusion layer, carbon cloth, nickel foam / mesh coated with carbon.

[0035] In an embodiment, the counter electrode is selected from graphite rod, platinum rod, and platinum mesh.

[0036] In an embodiment, the reference electrode is selected from Ag / AgCl electrode, Hg / Hg2SO4, standard hydrogen electrode, Hg / HgO, standard calomel electrode.

[0037] In an embodiment, the electrolyte is selected from perchloric acid, sulphuric acid, hydrocholric acid, potassium hydroxide, sodium hydroxide.

[0038] In another aspect, the present invention provides a full PEM fuel cell comprising: a) a cathode, b) an anode, c) gas diffusion layer, d) proton exchange membrane, e) electrolyte and f) said composite material, wherein the composite material is present in the fuel cell as coating layer onto said cathode,

[0039] In an embodiment, the full PEM fuel cell comprises a membrane electrode assembly (ME A) made by sandwiching anode, proton exchange membrane, and cathode.

[0040] BRIEF DESCRIPTION OF THE DRAWINGS:

[0041] Fig. 1 shows a schematic representation of the synthesis of Pt / 3D-PDC. Fig. 2 shows A) FESEM image of bare melamine sponge; B) and C) FESEM images of polydopamine coated and annealed melamine sponge; D) FEESEM image Pt / 3DPDPC; and E) and F) TEM images of Pt / 3DPDC, and G) the particle size distribution.

[0042] Fig. 3 shows A) the XRD profile of Pt / 3DPDC, B) the comparative Raman spectra of Pt / C (JM) and Pt / 3DPPDC, and C) the deconvoluted Pt4f XPS profile of Pt / 3DPDC.

[0043] Fig. 4 shows a) The CV profiles of Pt / C (JM) and Pt / 3DPDC recorded in 0.1 m HCIO4recorded at a scan rate of 50 mV s-1; and shows b) LSV comparison of Pt / C (JM) and Pt / 3DPDC in 0.1 M HCIO4at an electrode rotation speed of 1600 rpm.

[0044] Fig. 5 shows graphical data of Current (I) vs Time (h) conditioning data of: a) Pt / C (JM) with n / c = 0.6, b) Pt / 3DPPDC with n / c = 0.6, and c) Pt / 3DPPDC with n / c = 0.5 current of 70 A within 3.8 h, with a rate of 18.37 Ah1, and without any signs of flooding characteristics

[0045] Fig. 6 shows comparative I-V polarization curves recorded in a single-cell mode on the membrane electrode assemblies (MEAs) based on Pt / 3DPDPC and Pt / C (JM).

[0046] Fig. 7 shows a representative illustration of a full PEM fuel cell.

[0047] Fig. 8 shows a representative illustration of a half-cell setup.

[0048] Fig. 9 shows comparative I-V polarization curves recorded in single-cell mode on membrane electrode assemblies (MEAs) based on Pt / 3DPDPC with lower & higher n / c ratios. Here, n / c ratio means ratio of polymer based solid electrolyte and the graphitic carbon of the composite material.

[0049] DETAILED DESCRIPTION OF THE INVENTION

[0050] The terms “composite material”, “electrocatalyst”, “catalyst”, and “coating material onto membrane or electrode(s)” are used herein throughout the specification cover the same or nearly the same meaning where it comprises Ml metal nanoparticles, and nitrogen doped 3D graphitic carbon; wherein the Ml metal nanoparticles are dispersed or anchored over said nitrogen doped 3D graphitic carbon.

[0051] The term “catalyst NPs” used herein means metal nanoparticles acting as metal catalyst.

[0052] The term “support material” used herein means nitrogen doped 3D graphitic carbon. The terms “membrane”, “polymer membrane” and “material placed between electrodes”, used herein having the same meaning and are used interchangeably throughout the specification with meaning a component or material used in fuel cells, on which the composite material is coated, and here the triple phase boundary (TPB) of gas, liquid and solid is forming where the membrane is solid part of TPB. The examples of membranes are selected from but not limited to nafion, PBI, SPEEK, PAES, PPO and PI, all are in solid membrane form.

[0053] The terms “ionomers” and “polymer based solid electrolyte” used herein having the same meaning and used interchangeably throughout the specification, with the meaning of forming TPB of gas, liquid, and solid is forming where the ionomer is the liquid part of TPB. The examples of membranes are selected from but not limited to Nafion, PBI, SPEEK, PAES, PPO, and PI, all are in liquid or aqueous solution form.

[0054] In general embodiment, considering the above mentioned technical problems in the art, the present invention provides an incorporation of heteroatoms, like nitrogen, into the graphene structure and offers several benefits. Firstly, it accelerates the catalyst's nucleation and growth, leading to a smaller size and even distribution. Secondly, it strengthens the chemical bonding between the catalyst and support, resulting in improved stability. Lastly, it enhances electronic conductivity by modifying the electronic structure. Nitrogen has been considered an excellent dopant for graphene due to its high electronegativity and similar atomic size to carbon, making it the preferred choice among other dopants. Typically, the Pt nanoparticles are not fully exposed at the edges of the carbon support, leading to reduced activity as only a limited number of active centres are utilized. To address this issue, arranging the Pt nanoparticles within a three- dimensional (3D) carbon support structure can significantly boost the catalyst's overall activity by providing more accessible active centers.

[0055] The inventors have developed a simple strategy to overcome issues related to water management, mass transfer, charge transfer, and catalyst utilization. The size, shape, and distribution of the catalyst nanoparticles on the support materials significantly impact the device's performance. Additionally, support materials are crucial in regulating the properties of the catalyst, including high specific surface area, superior electrical conductivity for rapid electron transfer during the reactions, good electrochemical stability under harsh operating conditions, and strong immobilization of the catalyst to improve the triple phase boundaries in the PEMFC electrodes. In an embodiment, the present invention provides a composite material for coating electrode(s) or membrane of fuel cells, the composite material comprising: a) Ml metal nanoparticles, and b) nitrogen doped 3D graphitic carbon; wherein the Ml metal nanoparticles are dispersed or anchored over said nitrogen doped 3D graphitic carbon.

[0056] In some embodiments, the Ml metal is selected from noble metal elements or alloys forms or combinations thereof.

[0057] In some embodiments, the Ml metal is selected from noble metals such as platinum, palladium, silver, ruthenium, rhodium, iridium, or platinum alloys combined with other noble metals.

[0058] In some embodiments, the surface area of the composite material is in the range of around 950 to 1000 m2 / g; the composite material is microporous in nature with microporosity below 2 nm; and the pore volume of the composite material is in range of 0.5 to 0.9 cc / g.

[0059] In another embodiment, the Ml metal is selected from but not limited to Group X element, a mixture thereof, or alloy form thereof.

[0060] In another embodiment, the dispersion or anchoring comprises the presence of Ml NPs with an average particle size of more than or equal to 2.5 nm and less than or equal to 10 nm.

[0061] In another embodiment, the dispersion or anchoring comprises the presence of Ml NPs with an average particle size of less than or equal to 2.5 nm and more than or equal to 0.5 nm.

[0062] In another embodiment, the dispersion or anchoring comprises the presence of Ml NPs with an average particle size of approximately 2.5 nm.

[0063] Said smaller or nanometer sized particles possess a larger surface area relative to their volume, which allows for an increased number of active sites, thereby enhancing catalytic activity. For instance, as particle size decreases, the electrochemical active surface area (ECSA) increases, leading to higher mass activity and specific activity in catalysis in fuel cells.

[0064] In another embodiment, the dispersion or anchoring comprises the presence of Ml NPs throughout or onto the surface of the nitrogen doped 3D graphitic carbon. Specifically, the surface area of the composite material is around 993.7 m2 / g,

[0065] In another embodiment, the composite material is microporous in nature.

[0066] In specific embodiment, the composite material comprises particles with microporosity in the range of 1.6-2 nm.

[0067] In another embodiment, the Ml nanoparticles uniformly dispersed over the network-structured carbon in said composite material.

[0068] Specifically, Fig. 2e and 2f which confirms the uniform distribution of Ml nanoparticles over the network structured carbon.

[0069] Fig. 2g depicts the Ml nanoparticle size distribution over the network structured carbon

[0070] In another embodiment, the composite material comprises a mesh like structure formed for nitrogen doped 3D graphitic carbon having microporous nature.

[0071] In another embodiment, the composite material comprises higher active sites for Ml metal NPs in said nitrogen doped 3D graphitic carbon as interconnected network like structure.

[0072] Said Mesh like structure / specific orientation present in said nitrogen doped 3D structured graphitic carbon allows the smooth flow of gases / liquids / electrolyte in fuel cells.

[0073] It is submitted that the commercial Pt / C has a lesser surface area of around 250-300 and 450-500 m2 / g; and in contrast, the surface area of said composite material is higher i.e., in the range of 993.7 m2 / g.

[0074] In another embodiment, the present invention relates to a process of preparation of said composite material comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon, the process comprising steps of: i) preparing oxidative polymerized intermediate by reacting melamine sponge or polyurethane sponge with polydopamine or catechol containing polymer in the presence of buffer at temperature in the range of 20-40 °C for a time period of 20 to 28 h to form oxidative polymerized intermediate product; ii) annealing the intermediate product of step i) at a temperature in the range of 800 to 1000 °C for time period in the range of 2 to 4 h under an inert atmosphere to obtain an annealed product of nitrogen doped 3D carbon; and iii) decorating or anchoring Ml metal onto said annealed product of nitrogen doped 3D carbon of step ii) by reacting Ml metal precursor with said annealed product of nitrogen doped 3D carbon of step ii) in the presence of polyol or mixture of polyol and water at a temperature in the range of 110 to 150 °C for a time period in the range of 5 to 7.5 h to obtain said composite material comprising Ml metal nanoparticles dispersed or anchored over nitrogen doped 3D graphitic carbon.

[0075] In some embodiments, the Ml metal precursor is selected from chloroplatinic acid, potassium hexachloroplatinate, platinum(II) acetylacetonate, palladiumc(II) nitrate, plladium(II) chloride, tetraamminepalladium(II) chloride monohydrate, nickel(II) chloride, nickel(II) nitrate, nickel(II) acetylacetonate, cobalt(II) acetylacetonate, cobalt(II) nitrate hexahydrate, cobalt(II) chloride and combinations thereof; the polyol is selected from ethylene glycol, propylene glycol (PG), glycerol, diethylene glycol (DEG), triethylene glycol (TEG), 1,2-butanediol, and combinations thereof; and the buffer used in step i) is selected from bicarbonate buffer, tris-HCl Buffer (Tris(hydroxymethyl)aminomethane), Bicine (N,N-Bis(2-hydroxyethyl)glycine), Glycine-NaOH Buffer and combinations thereof.

[0076] In another embodiment, the Ml metal precursor is selected from but not limited to acetate, chlorides, sulfates or phosphates of Ml metal; wherein Ml metal is selected from transition metal elements.

[0077] In another embodiment, the Ml metal precursor is selected from but not limited to acetate, chlorides, sulfates or phosphates of Ml metal; wherein Ml metal is selected from Group X metal elements.

[0078] In another embodiment, the Ml metal precursor is selected from but not limited to acetate, chlorides, sulfates or phosphates of Ml metal; wherein Ml metal is selected from platinum, palladium, nickel, darmstadtium and Pt3Co alloy.

[0079] In specific embodiment the buffer used in step i) is bicarbonate buffer.

[0080] In another embodiment, the pH of step i) reaction mixture is in the range of 8 to 9.

[0081] Specifically, the pH of step i) reaction mixture is 8.5. In another embodiment, prior to annealing step ii), the process comprises drying of oxidative polymerized intermediate product under an infrared lamp for time period in the range of 9 to 14 h at a temperature in the range of 50-90 °C.

[0082] In another embodiment, the inert atmosphere in step ii) is attained by passing inert gas of neon, helium, argon or xenon.

[0083] In another embodiment, the annealing step ii) is done at a heating rate of 10 °C min-1.

[0084] In another embodiment, prior to step iii), the process further comprises acid-washing of the annealed product of nitrogen doped 3D carbon of step ii) with 0.5 M of acid H2SO4at a temperature in the range of 60 to 100 °C for a time period in the range of 3 to 5 h, followed by at least three times washing with deionized (DI) water and subsequent drying.

[0085] In another embodiment, the acid used for washing of step ii) product is selected from but not limited to HC1, H2SO4, HNO3, and so on.

[0086] In another embodiment, the mixture of polyol and water is used in step iii) with a ratio of 3: 1.

[0087] In another embodiment, step iii) further comprises preparing two solutions i.e., solution A of annealed product of nitrogen doped 3D carbon of step ii), and solution B of metal precursor with around 30 to 50 wt. % of Ml metal NPs.

[0088] In another embodiment, the solution B is prepared by adding a specific amount of Ml metal precursor so as to attain 30 to 50 wt. % of Ml metal NPs and polyol or a mixture of polyol and water, followed by sonicating the solution for 5 to 15 minutes to obtain solution B.

[0089] In another embodiment, the process further comprises slowly adding the solution B drop wise into the solution A under stirring for a time period in the range of 9 to 15 h at temperature in the range of 25 to 35 °C followed by heating, filtering, washing and drying to obtain the said composite material.

[0090] In a specific embodiment, said heating is done at a temperature in the range of 120 to 150 °C for a time period in the range of 6 to 10 h.

[0091] In a specific embodiment, the washing is done using deionized (DI) water at least two times. In specific embodiment, the drying is done at a temperature in the range of 100 to 140 °C in a vacuum oven for a time period of 6 to 18 h.

[0092] In another aspect, the present invention relates to a composition for fuel cells comprising an effective amount or ratio of polymer based solid electrolyte and the composite material, wherein said polymer based solid electrolyte acts as proton exchange material; the ratio of polymer based solid electrolyte (n) and the graphitic carbon (c) of the composite material is in the range of 0.4 to 0.8.

[0093] In another embodiment, said polymer based solid electrolyte is placed in contact with membrane material and / or electrode material wherein said membrane material and / or electrode material is coated with the composite material disclosed herein.

[0094] In some embodiments, the polymer based solid electrolyte is in aqueous solution form and is selected from nafion, polybenzimidazole (PBI), sulfonated polyether ether ketone (SPEEK), Poly(arylene ether sulfone) (PAES), Poly(phenylene oxide) (PPO), and Polyimide (PI); wherein the aqueous solution of polymer based solid electrolyte is in a concentration ranging between 5 to 20% w / v.

[0095] In another embodiment, the membrane material is in solid form and is selected from but not limited to nafion, polybenzimidazole (PBI), sulfonated polyether ether ketone (SPEEK), poly(arylene ether sulfone) (PAES), poly(phenylene oxide) (PPO), and polyimide (PI).

[0096] In another embodiment, the polymer based solid electrolyte or ionomer is in aqueous solution form and is selected from but not limited to nafion, polybenzimidazole (PBI), sulfonated polyether ether ketone (SPEEK), poly(arylene ether sulfone) (PAES), poly(phenylene oxide) (PPO), and polyimide (PI).

[0097] The nafion is a polytetrafluoroethylene (PTFE) backbone with perfluorinated-vinyl-polyether side chains containing sulphonic acid end groups.

[0098] In another embodiment, the aqueous solution of polymer based solid electrolytes or ionomers is in a concentration ranging between 5 to 20% w / v.

[0099] In another embodiment, ratio of polymer based solid electrolyte (n) and the graphitic carbon (c) of the composite material on which active sites are decorated is in the range of 0.4 to 0.8. This ratio is known as n / c ratio, where the inventors got results of effective activity of half and full fuel cells when the ratio is in the range of 0.4 to 0.8.

[0100] Above and below to this ratio, the performance is low (refer, Fig. 9).

[0101] In another embodiment, the 3D interconnected structure of the electrocatalyst support membrane or composite membrane, owing to its highly porous networked structure, enhances the triple phase boundary (TPB), which is the interface where the polymer based solid electrolyte, reactant gas, and electrically connected catalyst (i.e., composite membrane) come into contact with each other.

[0102] In another embodiment, the interconnected microporous carbon network of the composite membrane aids in withstanding high humidity while having no impact on the permeability of the reactant gases.

[0103] In another embodiment, the present invention relates to a half PEM fuel cell comprising said composite material as a coating layer onto electrode(s) or membrane placed over / in between electrode(s), wherein the cell comprises a working electrode, counter electrode, reference electrode, proton exchange membrane, and electrolyte, wherein the working electrode is selected from a carbon electrode, glassy carbon electrode, gas diffusion layer, carbon cloth, nickel foam / mesh coated with carbon; wherein the counter electrode is selected from graphite rod, platinum rod, and platinum mesh; wherein the reference electrode is selected from Ag / AgCl electrode, Hg / Hg2SC4, standard hydrogen electrode, Hg / HgO, standard calomel electrode; wherein the electrolyte is selected from perchloric acid, sulphuric acid, hydrocholric acid, potassium hydroxide, sodium hydroxide.

[0104] In another embodiment, the present invention relates to a full PEM fuel cell comprising said composite material as a coating layer onto electrode(s) or membrane placed between electrode(s).

[0105] In another embodiment, half fuel cell further comprises continuous purging of oxygen gas.

[0106] In another embodiment, the half fuel cell comprises 0.1 M HCIO4as the electrolyte, continuous purging of O2gas, composite membrane or electrocatalyst coated glassy carbon electrode as working electrode, graphite rod as counter electrode, and Ag / AgCl electrode employed as reference electrode.

[0107] In another aspect, the full fuel cell comprising a cathode, anode, composite membrane or electrocatalyst, gas diffusion layer, proton exchange membrane, and electrolyte; wherein the composite membrane or electrocatalyst is coated onto said proton exchange membrane.

[0108] In another aspect, the full fuel cell comprises a membrane electrode assembly (ME A) made by sandwiching an anode, proton exchange membrane, and a cathode.

[0109] In a nutshell, inventors have anchored Ml metal nanoparticles on Nitrogen doped 3D graphitic carbon to address the complexity that is currently present in the catalyst development. Polydopamine, an organic polymeric material, is grown in situ over a cheap, commercially available melamine foam, which, upon annealing, results in the formation of 3D structured graphitic carbon. The 3D interconnected structure of the electrocatalyst support membrane, owing to its highly porous networked structure, enhances the triple phase boundary (TPB), which is the interface where the electrolyte, reactant gas, and electrically connected catalyst come into contact. The 3D foam structure of the catalyst support material offers a perfect platform for several TPB sites throughout the porous network; however, the electrochemical reaction can only take place at TPBs when these zones are effectively connected to each other. These highly interconnected porous networks are large enough for the diffusion of reactant gas and favorable for the ionomer chains to penetrate and interact with the active sites for the maximum utilization of CL. In addition, 3D structural engineering on the carbon support morphology to spatially isolate the active site-bearing surfaces is an effective solution to eliminating mass transfer and water dissipation concerns. The relative humidity of incoming gases is normally maintained at a high value to make sure that the membrane is fully hydrated in order to maintain good proton conductivity. However, the pores of the catalyst layer (CL) and the gas diffusion layer (GDL) are frequently flooded by excessive liquid water, resulting in blockage of the catalyst surface and restricting reactant gas transport, which will lead to a mass transport resistance-related performance loss. Thus, a delicate balance must be maintained between membrane drying and liquid water flooding to prevent fuel cell breakdown and ensure good performance, which is the fundamental water management problem. In the traditional approach, increasing humidity is used to activate the CL quickly, but with time, the permeability of the CL to gas decreases. However, in this instance, the interconnected microporous carbon network aids in withstanding high humidity while having no impact on the permeability of the reactant gases.

[0110] EXAMPLES

[0111] The chemicals used herein are all procured from Sigma Aldrich, India and used without further purification.

[0112] Example 1: Synthesis of 3D Dopamine Carbon (3DPDC):

[0113] In a typical experiment, a solution of dopamine hydrochloride, with a concentration of approximately 3 mg / ml, was prepared in a bicarbonate buffer at pH 8.5. Commercially available melamine foam slices were immersed in this solution at a concentration of 1 mg / ml and stirred for a duration of 24 h. Subsequently, the melamine foam impregnated with polydopamine underwent a drying process under an infrared lamp for an entire night, followed by annealing in an argon (Ar) atmosphere at 900 °C for 3 h, utilizing a heating rate of 10 °C min-1. The resulting carbonized material was further subjected to acid-washing with 0.5 M H2SO4at 80 °C for 4 h, followed by triple washing with deionized (DI) water and subsequent drying. This material is henceforth denoted as 3DPDC.

[0114] Example 2: Synthesis of Platinum Supported on 3D Dopamine Carbon (Pt / 3DPDC):

[0115] The reduction of H2PtCl6, salt over 3D Dopamine Carbon (3DPDC) was carried out using the polyol method in ethylene glycol. A mixture of ethylene glycol and water, in a 3: 1 ratio, was prepared and separated into two portions. In one portion, 50 mg of 3DPDC was introduced and stirred for 1 hour, while the other portion, containing H2PtCl6, (corresponding to 40% Pt), was sonicated for 10 minutes and then slowly added drop wise into the solvent mixture containing 3DPDC using a burette. After completing the addition, the resulting solution was continuously stirred overnight. The solution was then heated to 140 °C for 8 h. The final catalyst was subsequently filtered, washed with deionized (DI) water, and subjected to drying at 120 °C in a vacuum oven, resulting in preparation of final catalyst, denoted as Pt / 3DPDC.

[0116] The synthesis of the Pt-supported onto 3D nitrogen doped graphitic carbon (Pt / 3DPDC) is schematically illustrated in Fig. 1. The synthesis involves three main steps. Firstly, polydopamine is coated onto the melamine foam. Then, the coated material is annealed at 900 °C for 3 h. Subsequently, acid washing is performed to remove the metal present in the material. Finally, Pt nanoparticles are decorated onto the 3D carbon using polyol synthesis. During the annealing process, the melamine foam undergoes conversion to carbon nitride, and the polydopamine that grew over it is transferred to the N-doped graphitic carbon. The amine groups in both dopamine and melamine foam contribute nitrogen, which is uniformly distributed over the graphitic carbon, leading to the creation of sites involving iron coordination. Melamine foam serves as a template for forming the 3D morphology and also acts as a nitrogen source for the doping process.

[0117] Characterization and structural analysis of synthesized Pt / 3DPDC:

[0118] Fig. 2a displays the FESEM image of the bare melamine foam, showing a smooth surface. Even after the polydopamine coating and subsequent high-temperature annealing, the structure of the melamine foam remains unchanged, as seen in Fig. 2b and 2c. Further, morphological characterization of Pt / 3DPPDC using FESEM reveals a network and porous structure, as depicted in Fig. 2d.

[0119] The TEM images (Fig. 2e and f) show Pt nanoparticles uniformly dispersed over the network- structured carbon.

[0120] The histogram (Fig. 2g) depicts the size distribution of Pt nanoparticles on the network- structured carbon, with an average particle size of 2.5 nm.

[0121] The powder X-ray diffraction (XRD) pattern of Pt / 3DPDC (in Fig. 3a) exhibits identical peak positions corresponding to both the Pt nanoparticles and the carbon support materials. The peaks at 2θ values of 39.6° (111), 45.4° (200), and 68.1° (220) are attributed to different planes of Pt (JCPDS: 87-0647), indicating the presence of a face-centred cubic crystal lattice of Pt nanoparticles in a crystalline state. The support materials used here is conducting carbon which displays the same peaks corresponding to carbon (2θ values of 26.3°).

[0122] Fig. 3b presents a comparison of the Raman spectra between state-of-the-art Pt / C (40% Pt on 60% C) (JM - Johnson Matthey), and Pt / 3DPDC of the present invention. Although both materials show similar Raman shift values for the G and D bands frequencies, the catalysts differ in terms of the intensity ratio between the D and G bands. The G and D bands appear at 1590 and 1334 cm-1, respectively. The G band indicates the presence of graphitic content and originates from the zone-center Eig mode, while the D band corresponds to the peak caused by disorder in the graphite lattice and is associated with the A1gzone-edge phonon. Thus, the G band represents sp2carbons in the hexagonal framework of the carbon, whereas the D band indicates defective sp3carbons formed within the sp2carbon lattice. Calculating the ratio of intensities between the defective and graphitic bands provides valuable information about the defects in the carbon morphologies. The ID / IG ratio for Pt / 3DPDC and Pt / C (JM) is 1.25 and 1.12, respectively, indicating that nitrogen doping creates defects in Pt / 3DPDC.

[0123] X-ray photoelectron spectroscopy (XPS) analysis can provide valuable insights into the nature and condition of the catalytic systems. In the case of Pt / 3DPDC, the Pt 4f XPS spectra display two characteristic peaks at different binding energy values, representing Pt 4f5 / 2and Pt 4f7 / 2, respectively (Fig. 3c). These Pt 4f signals can be further broken down into three doublets, each corresponding to distinct states: Pt° state, Pt2+state, and Pt4+state. The doublets with lower binding energies, such as 71.9 and 75.3 eV, are associated with the metallic Pt particles (Pt°), while the ones with higher binding energies indicate the presence of surface oxidized Pt species (Pt4+). Additionally, XPS analysis reveals existence of electron deficient and atomically dispersed Pt particles, formed as Pt2+on graphitic carbon surface.

[0124] Example 3: Analysis and testing of said synthesized Pt / 3DPDC in fuel cell:

[0125] The catalysts were initially evaluated through cyclic voltammetry (CV) in 0.1 M HCIO4, using Ag / AgCl as the reference electrode and a graphite rod as the counter electrode. Fig. 4a presents a comparison of the CVs for Pt / 3DPDC and commercially available Pt / C (JM) in N2-saturated 0.1 m HCIO4at a scan rate of 50 mV s-1. The CV profiles exhibit typical Pt characteristics, showing regions associated with hydrogen adsorption-desorption, oxygen adsorption-desorption, and non-faradaic capacitance. The electrochemically active surface area (ECSA) was determined from hydrogen desorption, resulting in ECSA values of 48.5 m2g-1for Pt / 3DPDC and 55.5 m2g-1for Pt / C (JM). Fig. 4b displays the Linear sweep voltammograms (LSVs) for oxygen reduction reaction (ORR) recorded at 1600 rpm in oxygen- saturated 0.1 M HCIO4. The LSV of the state- of-the-art Pt / C JM catalyst is also included for comparison. Among the four catalysts, Pt / 3DPDC exhibited the highest onset potential (0.982 V vs. RHE) followed by Pt / C JM (0.969 V vs. RHE). However, the difference in the onset potential becomes more pronounced in the half-wave potential (E1 / 2) region, which is a crucial parameter for assessing the catalyst's ability to facilitate ORR under realistic current dragging conditions. In this regard, Pt / 3DPDC demonstrated a substantially higher E1 / 2 value (0.852 V vs. RHE) compared to Pt / C JM (0.822 V vs. RHE). This advantage is mainly attributed to Pt / 3DNG's unique structural features, providing improved reactant distribution and active site accessibility. Consequently, Pt / 3DPDC outperforms other systems in terms of E1 / 2 under current dragging condition due to its distinct structural characteristics. Followed by the promising single electrode results obtained in the case of Pt / 3DPDC toward ORR, a realistic system level validation has been performed by testing a single cell of a low- temperature PEMFC (LT-PEMFC). Due to the advantageous features as understood from the previous discussions, the Pt / 3DPDC based electrode is expected to be a better contender for the LT-PEMFC (Low Temperature Proton Exchange Membrane Fuel Cell) application. The membrane electrode assembly (MEA) was fabricated by interleaving a catalyst-coated membrane (CCM) between gas diffusion layers (GDL). Subsequently, single cell testing was conducted on the MEAs with a 45 cm2active area, under Hi-air feed conditions. The performance evaluation primarily involved state-of-the-art Pt / C (JM) catalyst, employing the usual Nafion to carbon (n / c) ratio of 0.6. However, the attainment of the maximum output current of 55 A, at a rate of 5.77 Ah1, required approximately 8 h. Analysis of the conditioning data in Fig. 5a reveals signal irregularities during the process, suggestive of water molecule flooding. Similarly, the indigenous Pt / 3DPDC catalyst (Fig. 5b) was subjected to the same procedure, taking around 8 h at a rate of 6.40 Ah1, yet no noisy peaks were observed, indicating superior water management. Subsequently, the n / c ratio was further reduced to 0.5 for Pt / 3DPDC, resulting in a remarkable achievement of a maximum current of 70 A within 3.8 h, with a rate of 18.37 Ah1, and without any signs of flooding characteristics (Fig. 5c).

[0126] Fig. 6 depicts the comparative I-V polarization plots obtained during the evaluation of a single cell membrane electrode assembly (MEA). The MEA is based on Pt / C (JM) with an n / c ratio of 0.6, and Pt / 3DPPDC with two distinct n / c ratios, namely 0.5 and 0.6. The polarization plots of all MEAs exhibit well-defined features, spanning across the activation, ohmic, and mass transfer regions. Upon closer examination, the MEA utilizing Pt / C (JM) exhibits superior performance compared to the counterpart system using Pt / 3DPDC with n / c = 0.6. Notably, the Pt / 3DPDC with n / c = 0.5 demonstrates a significant performance improvement compared to the other two MEAs. This performance increment is directly linked to the current density, leading to a remarkable disparity in the maximum power density displayed by all systems. This significant difference can be attributed to the in-house system's enhanced ability to effectively address mass transfer requirements, particularly under high current conditions, owing to its favorable morphological characteristics. Moreover, it is worth mentioning that even at 0.60 V, which corresponds to one of the standard operating potential regions of a proton exchange membrane fuel cell (PEMFC), the Pt / 3DPDC with n / c = 0.5 achieves a notable current density of 1.13 A cm-2, surpassing Pt / 3DPDC and Pt / C (JM) with n / c = 0.5 systems, which achieved current densities of 0.85 and 0.96 A cm-2, respectively. ADVANTAGES OF THE INVENTION

[0127] • The present invention provides better water management by using composite material in fuel cells, e.g. the humidity level of the incoming gases is typically maintained at a high value to ensure full hydration of the membrane in said fuel cells, thereby promoting optimal proton conductivity. However, an issue arises when excessive liquid water floods the pores of the Catalyst Layer (CL) and the Gas Diffusion Layer (GDL), leading to the blockage of catalyst surfaces and hindering the transport of reactant gases. This, in turn, results in a decline in performance due to mass transport resistance. Therefore, achieving an appropriate balance between membrane drying and liquid water flooding is essential to prevent fuel cell breakdown and ensure optimal performance, which constitutes the fundamental challenge of water management. In traditional approaches, high humidity is employed to rapidly activate the CL, but over time, it diminishes the gas permeability of the CL. However, in this particular case, the interconnected microporous carbon network of the CL effectively withstands high humidity without affecting the permeability of the reactant gases. The highly porous structure facilitates the efficient dissipation of excess water molecules.

[0128] • The potential of enhancing triple phase boundaries and creating high-performance fuel cell electrodes lies in the three-dimensional hierarchical and porous structures of the composite membrane materials as disclosed herein. These possess a significant specific surface area, distinctive porous architecture, a substantial level of heteroatom doping, excellent mechanical stability, and multiple pathways for electrical conduction.

[0129] • The present invention emphasizes the use of a 3D-structured carbon material with a high surface area, which facilitates the formation of a more efficient triple-phase boundary. This improved boundary enhances the interaction between the liquid electrolyte, gas reactant, and solid electrocatalyst surface, leading to significantly higher performance. Additionally, the unique 3D carbon structure improves mass transport, enabling the fuel cell to activate within 1.5 hours, a notable improvement over the 6-hour activation time reported in other works. This structure also provides process-friendly advantages for PEMFC electrode fabrication, minimizing flooding issues and allowing faster activation with lower energy requirements. Overall, the high surface area and optimized 3D structure contribute to superior catalytic performance, faster activation, and improved efficiency, distinguishing the present invention from literature known materials.

[0130] • Provides better activity in terms of efficient ORR reactions in fuel cells. • Provides mesh like structure / specific orientation present in said N2 doped 3D structured graphitic carbon which allows smooth flow of gases / liquids / electrolyte.

[0131] • Provides higher surface area with improved electrocatalytical activity lesser agglomeration of Ml metal NP in composite. • Provides higher active sites on composite with specific network of carbon.

[0132] • Provides higher mechanical strength and provides higher pore volume.

[0133] • Provides efficient N2 doping using polydopamine.

[0134] • Provides the composite material comprising carbon nitride backbone.

[0135] • The composite material provides better activation energy within lesser period of time during electrochemical testing (9 h vs 4 h).

[0136] • Provides higher mass and electron transport.

Claims

AMENDED CLAIMS received by the International Bureau on 15 April 2025 (15.04.2025)1. A composite material for coating electrode(s) or membrane of fuel cells, the composite material comprising: i. Ml metal nanoparticles, and ii. nitrogen doped 3D graphitic carbon; wherein the Ml metal nanoparticles are anchored over said nitrogen doped 3D graphitic carbon; wherein metal of said Ml metal nanoparticles is selected from noble metal, alloy of noble metals, and alloy of noble metal and transition metal; and wherein surface area of the composite material is in the range of around 950 to 1000 m2 / g.

2. The composite material as claimed in claim 1, wherein the noble metal is selected from platinum, palladium, silver, ruthenium, rhodium, or iridium, and the transition metal is selected from cobalt, nickel, tin, manganese, copper and tungsten.

3. The composite material as claimed in claim 1, wherein the composite material is microporous in nature with microporosity below 2 nm; a particle size of the Ml metal nanoparticles is in the range of 1 to 5 nm; and a pore volume of the composite material is in range of 0.5 to 0.9 cc / g.

4. A process of preparation of composite material as claimed in claim 1, the process comprising steps of: i) preparing an oxidative polymerized intermediate by reacting a melamine sponge or a polyurethane sponge with polydopamine or catechol containing a polymer in the presence of a buffer at a temperature in the range of 20 to 40 °C for a time period of 20 to 28 h to form the oxidative polymerized intermediate; ii) annealing the intermediate of step i) at a temperature in the range of 800 to 1000 °C for a time period in the range of 2 to 4 h under an inert atmosphere to obtain an annealed product of nitrogen doped 3D carbon; and iii) anchoring Ml metal nanoparticles onto said annealed product of nitrogen doped 3D carbon of step ii) by reacting a Ml metal precursor with said annealed product of step ii) in the presence of a polyol or a mixture of polyol and water at a temperature in the range of 110 to 150 °C for a time period in the range of 5 to 7.5 h to obtain the composite material.

5. The process as claimed in claim 4, wherein metal in said Ml metal precursor is selected from noble metal, alloy of noble metals, and alloy of noble metal and transition metal, wherein thenoble metal is selected from platinum, palladium, silver, ruthenium, rhodium, or iridium, and the transition metal is selected from cobalt, nickel, tin, manganese, copper and tungsten.

6. The process as claimed in claim 4 or 5, wherein the Ml metal precursor is selected from chloroplatinic acid, potassium hexachloroplatinate, platinum(II) acetylacetonate, palladium(II) nitrate, palladium(II) chloride, tetraamminepalladium(II) chloride monohydrate, nickel(II) chloride, nickel(II) nitrate, nickel(II) acetylacetonate, cobalt(II) acetylacetonate, cobalt(II) nitrate 10 hexahydrate, cobalt(II) chloride and combinations thereof.

7. The process as claimed in claim 4, wherein the polyol is selected from ethylene glycol, propylene glycol (PG), glycerol, diethylene glycol (DEG), triethylene glycol (TEG), 1,2- butanediol and combinations thereof.

8. The process as claimed in claim 4, wherein the buffer used in step i) is selected from 15 bicarbonate buffer, tris-HCl buffer (tris(hydroxymethyl)aminomethane), bicine (N,N-bis(2- hydroxyethyl)glycine), glycine-NaOH buffer and combinations thereof.

9. The process as claimed in claim 4, wherein prior to step iii), the process comprises acid- washing of the annealed product of nitrogen doped 3D carbon of step ii) with 0.5 M of acid H2SO4at a temperature in the range of 60 to 100 °C for a time period in the range of 3 to 5 h, 20 followed by at least three times washing with deionized (DI) water and subsequent drying.

10. A composition for fuel cells, comprising: an effective amount or ratio of a polymer based solid electrolyte and the composite material as claimed in claim 1, wherein said polymer based solid electrolyte act as proton exchange material; and wherein the ratio of polymer based solid electrolyte and the graphitic carbon of the composite material is in range of 0.4 to 0.8.

11. The composition as claimed in claim 10, wherein the polymer based solid electrolyte is in aqueous solution form and is selected from nafion, polybenzimidazole (FBI), sulfonated polyether ether ketone (SPEEK), poly(arylene ether sulfone) (PAES), poly(phenylene oxide) (PPO), and polyimide (PI); and wherein the aqueous solution of polymer based solid electrolyte is in concentration ranging between 5 to 20% w / v.

12. A half proton exchange membrane (PEM) fuel cell comprising: a) a working electrode, b) a counter electrode, c) a reference electrode, d) a proton exchange membrane, e) an electrolyte, and’ f) the composite material as claimed in claim 1,wherein the composite material is present in the fuel cell as coating layer onto said working electrode or as a membrane placed over / in between electrodes of a), b) or c).

13. The half PEM fuel cell as claimed in claim 12, wherein the working electrode is selected from a carbon electrode, glassy carbon electrode, gas diffusion layer, carbon cloth, nickel foam / mesh coated with carbon; wherein the counter electrode is selected from graphite rod, platinum rod, and platinum mesh; wherein the reference electrode is selected from Ag / AgCl electrode, Hg / Hg2SO4, standard hydrogen electrode, Hg / HgO, standard calomel electrode; wherein the electrolyte is selected from perchloric acid, sulphuric acid, hydrocholric acid, potassium hydroxide, sodium hydroxide.

14. A full PEM fuel cell comprising: a) a cathode, b) an anode, c) a gas diffusion layer, d) a proton exchange membrane, e) an electrolyte and f) the composite material as claimed in claim 1, wherein the composite material is present in the fuel cell as coating layer onto said cathode, anode or gas diffusion layer, or as a membrane placed over / in between a), b) or c).STATEMENT UNDER ARTICLE 19 (1 )With reference to the search report and written opinion of ISA / IN, the applicant has amended claims to address the clarity and inventive step objections.

1. The Applicant submits that claim 1 has been amended by adding the features of claim 3.

2. The Applicant submits that claim 3 has been deleted accordingly.

3. The Applicant submits that claims have been renumbered accordingly.The Applicant undertakes that no new subject matter has been added in claims and the amended claims do not go beyond disclosure of international application as-filed.

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