WO2023170485A1

WO2023170485A1 - Composition for catalyst ink comprising ferricyanide-ferrocyanide and process for preparing the same

Info

Publication number: WO2023170485A1
Application number: PCT/IB2023/051146
Authority: WO
Inventors: Surendra Singh GAUR; V M K Kireeti KOTA
Original assignee: Dre Motors Private Limited
Priority date: 2022-03-10
Filing date: 2023-02-09
Publication date: 2023-09-14

Abstract

The present disclosure provides a composition for a catalyst ink comprising a ferricyanide- ferrocyanide redox couple for a fuel cell membrane electrode assembly. The present disclosure also provides a process for preparing a catalyst ink comprising a ferricyanide- ferrocyanide redox couple, the process comprising incorporation of a ferricyanide- ferrocyanide redox couple directly into the catalyst ink. Further, the present disclosure provides a catalyst coated membrane to be used in PEM fuel cell, where the catalyst ink comprising of a ferricyanide-ferrocyanide redox couple. The membrane when coated with the catalyst ink comprising a ferricyanide-ferrocyanide redox couple, its durability and life was increased.

Description

COMPOSITION FORCATALYST INK COMPRISINGFERRICYANIDE- FERROCYANIDE AND PROCESS FOR PREPARING THE SAME

FIELD OF INVENTION

[0001] The present disclosure relates to the field of a catalyst ink for a fuel cell membrane. In particular, the present disclosure provides a composition for a catalyst ink comprising a ferricyanide-ferrocyanide redox couple for a fuel cell membrane electrode assembly (MEA). Further, the present disclosure provides a process for preparing a catalyst ink for a fuel cell MEA with increased durability of the membrane, the process comprising incorporation of a ferricyanide-ferrocyanide redox couple directly into the catalyst ink.

BACKGROUND OF THE INVENTION

[0002] Membrane durability is one of the major issues in the existing polymer electrolyte membrane fuel cell (PEMFC) technology. Chemical degradation is one of the reasons for low life cycle of the solid polymer electrolyte membrane (PEM) used in fuel cells. The main reason for the chemical degradation of the membrane is attack of free radicals formed during electrochemical reaction on the different functional sites present in the electrolyte membrane. In perfluorinated membranes, the most commonly used membranes in PEM fuel cells, these free radicals are found to attack carboxyl end groups, sulfonate groups, ether groups and tertiary carbon. H-containing groups are also known to be unstable. The formation of H₂O₂ and its subsequent conversion to free radicals in presence of transition metal ions like Fe²⁺ leads to chemical degradation. The equation (1) and equation (2) show the formation of free radicals through Fenton's reaction in presence of H₂O₂ and Fe ions.

(1) H₂O₂ + Fe²⁺ Fe³⁺ + OH. + OH’

(2) H₂O₂ + Fe³⁺ Fe²⁺ + OOH. + OH⁺

[0003] The perfluorosulfonic acid (PF SA) membranes are the most commonly used membranes in PEM fuel cells. The following reaction scheme shows the possible mechanism of degradation of different functionalities present in PFSA membrane in presence of free radicals.

[0004] To address this issue and to enhance the durability of the membrane, the common practice is to replace reactive functional groups with stable unreactive groups. Other methods include use of hydrogenperoxide decomposition agents, metal chelating agents, free radical scavengers or use of antioxidant.

[0005] Adding free radical scavengers in electrocatalyst is one approach. Incorporation of free radical scavenger like ceria or ferricyanide-ferrocyanide in to the membrane has been found to be one of the good alternatives where these radical scavengers selectively react to the free radicals to consume them; they can be easily regenerated and are not easy to wash out in acidic media. [0006] Ceria and its derivatives are one of the most common materials used for free radical scavenging. Redox reaction between Ce₂O₃ and CeO₂ provides capability to work as suitable free radical scavenger. There have been different methods to incorporate ceria in the fuel cell components to utilize it as radical scavenger. Ceria or its derivatives have been directly added to solid electrolyte membrane by ion exchange methods or during the membrane fabrication have been added to the polymer. But the Ceria compounds are known to dissolve in acid environment leading to partial to almost complete removal of these elements during the acidic pretreatment of the membrane. As the environment in electrolyte membrane during the operation is also acidic, it will again cause continuous loss of ceria based scavengers. Similar issues are faced when ceria or its compounds are incorporated in catalyst layer or gas diffusion layer due to acidic working environment. Another issue encountered with ceria based compounds is that they may coordinate with sulfonic acid functionalities present in PFSA membranes to reduce the proton conductivity of the membrane.

[0007] To replace the ceria or its derivatives to solve the polymer electrolyte membrane durability issues, recently, incorporation of the ferrocyanide-ferricyanide (Fc (II)-Fc (III)) redox couple has been considered.

[0008] A typically approach to incorporate Fc (II)-Fc (III) redox couple is to include ferrocyanide-ferricyanide additives by physical or ligand exchange on electrolyte membrane. However, addition of free radical scavengers in the PEM or the electrocatalyst ink requires extra steps such as physical-chemical treatment, pre-processing chemical pretreatment, extra layering or different steps thereby making the respective synthesis process very complex, cumbersome, and more time consuming. At the same time, it results in extra cost of fabrication making the process costly and non-feasible. Another challenge includes achieving uniform dispersion and distribution of the free radical scavengers in the PEM, which is difficult to achieve, thereby compromising the stability of the PEM.

[0009] Therefore, there exists an unmet need in the art to provide a suitable means and a manner for directly incorporating a ferrocyanide-ferricyanide (Fc (II)-Fc (III)) redox couple as a free radicle scavenger in a catalyst ink overcoming one or more challenges of requiring additional complex, cumbersome, more time consuming processing steps for example a preprocessing chemical treatment, extra layering or different steps resulting in extra cost of fabrication; and achieving a uniform dispersion of the ferrocyanide-ferricyanide (Fc (II)-Fc (III)) redox couple in the catalyst ink and thereby distribution on the membrane surface coated with said catalyst ink to increase the stability of the polymer electrolyte membrane (PEM) used in fuel cells. OBJECTS OF THE INVENTION

[00010] An object of the present disclosure is to provide a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt capable of providing the ferricyanide-ferrocyanideredox couple.

[00011] Another object of the present disclosure is to provide a process for preparing a catalyst ink comprising a ferricyanide-ferrocyanide redox couple.

SUMMARY

[00012] In an aspect, the present disclosure provides a catalyst ink in which the Fc (II)-Fc (III) redox couple is incorporated in the catalyst ink itself as against aprevious approach of including the ferricyanide-ferrocyanide additives in electrolyte membrane.

[00013] In an aspect of the present disclosure, there is provided a composition for a catalyst ink for a fuel cell membrane electrode assembly (MEA), the composition comprising ferricyanide or ferrocyanide salt capable of providing the catalyst ink containing the ferricyanide-ferrocyanide redox couple.

[00014] In one aspect, the present disclosure provides a composition for a catalyst ink for a fuel cell MEA, the composition comprising ferricyanide or ferrocyanide salt capable of providing the catalyst ink containing a ferricyanide-ferrocyanide redox couple as a free radical scavenger to increase the stability of the fuel cell membrane used in fuel cells.

[00015] In one aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and organic solvent(s) selected from alcohol and polyol.

[00016] In one aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and alcohol.

[00017] In one aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and a mixture of alcohol and polyol.

[00018] In one more aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and organic solvent(s) selected from alcohol and polyol, wherein the Pt-C catalyst comprises Pt loading on carbon ranging from about 10 wt% to about 70 wt%, the ratio of PFSA ionomer to carbon being in the range from about 2:5 to 1 : 1, the ratio of carbon to solvent system being in the range from about 1 :5 to about 1 :30, and the ratio of water to organic solvent(s) being in the range from about 1 : 1 to about 1 :5.

[00019] In an aspect, the present disclosure provides a process for preparing a catalyst ink for coating a polymer electrolyte membrane used in PEM fuel cells.

[00020] In one aspect, the present disclosure provides a process for preparing a catalyst ink containing a ferricyanide-ferrocyanide redox couplefor coating a membrane electrode assembly (MEA) of a fuel cell to increase stability and/or life of said membrane.

[00021] In one aspect, the present disclosure provides a process for preparing a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the process being simple, without requiring additional processing step(s) like pre-processing, or extra layering or the like.

[00022] In one aspect, the present disclosure provides a process for preparing a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the process comprising incorporating the ferricyanide-ferrocyanide redox couple as a free radical scavenger directly in the catalyst ink without requiring pre-processing step(s) while achieving uniform dispersion of the ferricyanide-ferrocyanide redox couple in the catalyst ink.

[00023] In one aspect, the present disclosure provides a process for preparing a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the process comprising: a) mixing a catalyst with ferricyanide or ferrocyanide salt in a solvent system; b) adding ionomer in the mixture obtained in step (a) and mixing to obtain an ink; c) homogenizing the ink by a probe sonication; and d) homogenization the ink obtained in step (c) in sonication bath to obtain the catalyst ink containing a ferricyanide-ferrocyanide redox couple.

[00024] In certain aspects, the present disclosure provides catalyst coated membrane by coating the membrane with the catalyst ink containing the ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple of the present invention.

[00025] In further aspect, the present disclosure provides a process for providing a catalyst coated membrane (CCM), the process comprising: i) preparing catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple, the process comprising: a) mixing a catalyst with ferricyanide or ferrocyanide salt in a solvent system, b) adding ionomer in the mixture obtained in step (a) and mixing to obtain an ink, c) homogenizing the ink by a probe sonication, and d) homogenizing the ink in sonication bath to obtain the catalyst ink containing ferricyanide-ferrocyanide redox couple; and ii) coating a perfluorosulfonic acid (PFSA) membrane with the catalyst ink containing the (Fc (II)-Fc (III)) redox couple obtained in step (i) by steps comprising: a) coating the catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple on a polymeric film; b) drying the catalyst ink coated polymeric film at a temperature ranging from about 80°C to about 150°C; c) repeating steps (a) and (b) to achieve catalyst ink loading on the film; d) transferring the catalyst layer from the catalyst coated film to a perfluorosulfonic acid (PFSA) membrane by pressing a side of the film coated with the catalyst ink with the PSFA membrane in a hot press, maintaining the hot press at a temperature in the range of about 100°C to about 140°C and pressure in the range of about 60 bar to 130 bar for about 2 minutes to about 10 minutes to provide a catalyst coated membrane; and e) peeling off the film from the catalyst coated membrane.

[00026] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

DETAILED DESCRIPTION OF THE INVENTION

[00027] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features.

[00028] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[00029] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[00030] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[00031] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.

[00032] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.

[00033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.

[00034] All methods described herein can be performed in suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[00035] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[00036] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[00037] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[00038] Terms “catalyst ink” and “electrocatalyst ink” are used interchangeably and mean the same that is a catalyst ink.

[00039] The present disclosure in general relates to providing a catalyst ink comprising ferricyanide-ferrocyanide redox couple, said catalyst ink being suitable for coating apolymer electrolyte membrane (PEM) used in fuel cells.

[00040] The present disclosure is directed to providing a catalyst ink comprising ferricyanide-ferrocyanide redox couple capable of increasing the life of fuel cell membrane when coated with said catalyst ink.

[00041] In an embodiment, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprises ferricyanide or ferrocyanide salt capable of providing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple as a free radical scavenger to increase the stability of the polymer electrolyte membrane (PEM) when coated with said catalyst ink.

[00042] In one embodiment, the present disclosure provides a composition for catalyst ink containing ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; and solvent system comprising water and organic solvent(s) selected from alcohol and polyol.

[00043] In one aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and alcohol.

[00044] In one aspect, the present disclosure provides a composition for a catalyst ink containing a ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; a solvent system comprising water and a mixture of alcohol and polyol.

[00045] In one embodiment the ferricyanide or ferrocyanide salt is a potassium ferricyanide or potassium ferrocyanide salt, other possible salts can be selected from the group consisting of but not limiting to ammonium ferrocyanide, ammonium ferricyanide, sodium ferricyanide, sodium ferrocyanide, and iron ferrocyanide, or combinations thereof.

[00046] In embodiments of the present invention, water used is deionized (DI) water.

[00047] In one embodiment, the alcohol is selected from but not limiting to Cl to C6 alcohol or combination thereof.

[00048] In one embodiment, the polyol is selected from but not limiting to ethylene glycol, glycerol, propanediol or the like, or combinations thereof.

[00049] In one embodiment, potassium ferrocyanide or potassium ferricyanide is present in the composition from about 2% to about 20%, preferably from about 2% to about 10%, more preferably from about 2% to about 5% on w/w basis of solid content.

[00050] In one embodiment, the Pt-C catalyst comprises Pt loading on carbon ranging from about 10% to about 70 wt% of carbon.

[00051] In one embodiment, theratio of PFSA ionomer to carbon is present in the range from about 2:5 to about 1 : 1.

[00052] In one embodiment, the ratio of carbon to solvent system is present in the range from about 1 :5 to about 1 :30.

[00053] In one embodiment, the ratio of water to organic solvent is in the range from about 1 : 1 to about 1 :5.

[00054] In one embodiment, the ratio of alcohol to polyolis in the range from about 3: Ito about 1 :2. [00055] In one embodiment, the present disclosure provides a composition for catalyst ink containing ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; and a solvent system comprising water and organic solvent selected from alcohol and polyol, wherein the Pt-C catalyst comprises Pt loading on carbon ranging from about 10% to about 70 wt% of carbon, ratio of PFSA ionomer to carbon being in the range of about 2:5 to about 1 : 1, ratio of carbon to solvent system being in the range of about 1 :5 to about 1 :30, and ratio of DI water to organic solvent(s) being about 1 : 1 to about 1 :5.

[00056] In another embodiment, the present disclosure provides a process for preparing a catalyst ink for coating polymer electrolyte membrane used in PEM fuel cell.

[00057] In one embodiment, the present disclosure provides a process for preparing a catalyst ink containing ferricyanide-ferrocyanide redox couple, said catalyst ink containing ferricyanide-ferrocyanide redox couple being suitable for coating the fuel cell membrane to increase stability and/or life of the membrane.

[00058] In one embodiment, the present disclosure provides a process for preparing a catalyst ink containing ferricyanide-ferrocyanide redox couple, the process comprising incorporation of ferricyanide-ferrocyanide redox couple as a free radical scavenger directly in the catalyst ink without requiring pre-processing step(s) while achieving uniform dispersion of ferricyanide-ferrocyanide redox couple in the catalyst ink.

[00059] In one aspect, the present disclosure provides a process for preparing a catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple, the process comprising: a) mixing a catalyst with ferricyanide or ferrocyanide salt in a solvent system; b) adding ionomer in the mixture obtained in step (a) and mixing to obtain an ink; c) homogenizing the ink by a probe sonication; and d) homogenizing the ink in sonication bath to obtain ferricyanide-ferrocyanide redox couple incorporated catalyst ink.

[00060] The process for preparing a catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple in accordance with the present disclosure is simple without requiring additional processing step(s) like pre-processing, or extra layering or the like. [00061] In certain embodiment, the present disclosure provides catalyst coated membrane by coating the membrane with the catalyst ink containing the ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple of the present invention.

[00062] In further aspect, the present disclosure provides a process for providing a catalyst coated membrane (CCM), the process comprising: i) preparing catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple, the process comprising: a) mixing a catalyst with ferricyanide or ferrocyanide salt in a solvent system, b) adding ionomer in the mixture obtained in step (a) and mixing to obtain an ink, c) homogenizing the ink by a probe sonication, and d) homogenizing the ink in sonication bath to obtain the catalyst ink containing ferricyanide-ferrocyanide redox couple; and ii) coating a perfluorosulfonic acid (PFSA) membrane with the catalyst ink containing the (Fc (II)-Fc (III)) redox couple obtained in step (i) by steps comprising: a) coating the catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple on a polymeric film; b) drying the coated polymeric film at a temperature ranging from about 80°C to about 150°C; c) repeating steps (a) and (b) to achieve catalyst ink coating on the film; d) transferring the catalyst layer from the catalyst coated film to a perfluorosulfonic acid (PFSA) membrane by pressing a side of the film coated with the catalyst ink with the PSFA membrane in a hot press, maintaining the hot press at a temperature in the range of about 100°C to about 140°C and pressure in the range of about 60 bar to 130 bar for about 2 minutes to about 10 minutes to provide a catalyst coated membrane; and e) peeling off the film from the catalyst coated membrane.

[00063] In an embodiment, in the step (ii), the step (c) that is repeating of steps (a) and (b) is carried out until desired loading of the catalyst ink is achieved. [00064] The same process can be used for both anode and cathode side, but generally one side is directly coated on the membrane and other is transferred on membrane by decal transfer method, while maintaining the desired Pt loadings.

[00065] In an embodiment, in the step (ii), drying of the coated polymeric film in step (b) is carried out on hot vacuum plate while keeping the temperature in range from about 80°C to about 150°C.

[00066] In certain embodiments, the loading for the cathode application can range from about 0.1 mg/cm²to 0.5 mg/cm².

[00067] The polymeric film that may be used for coating the catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple in step (a) of step (ii) can be any suitable polymeric film such as perfluorosulfonic acid (PFSA) based membranes, partially fluorinated, non-fluorinated, acid-base blends or other composite membranes.

[00068] The membrane if desired can be subjected to a prior acid treatment to convert the used potassium ferrocyanide or potassium ferricyanide to its acid form. In the proposed methodology it is believed that the inclusion of the ferricyanide-ferrocyanide redox couple in the catalyst ink acts as free radical scavengers and helps increase the stability of the polymer electrolyte membrane (PEM) used in fuel cells when the membrane is coated with said catalyst ink. The presence of ferricyanide-ferrocyanide redox couple also enhances the proton transport from thecatalyst surface to three phase boundary layers along with scavenging the free radicles formed during the electrochemical reaction.

[00069] It was unexpectedly found that the durability of the catalyst coated membrane was improved significantly, thereby increasing the life of the PFSA membrane. The improvement in life cycle is found to be in range of 1.5 to 10 times in by using different combinations of Fc (II)-Fc (III) redox couple, catalyst, and solvents.

[00070] Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible.

[00071] The present disclosure satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

ADVANTAGES OF THE PRESENT INVENTION

[00072] The catalyst ink provided in accordance with the present disclosure containing a Fc (II)-Fc (III) redox couple acting as a radical scavenger helps increasing the durability of the polymer electrolyte membrane used in PEM fuel cell, when said membrane is coated with the catalyst ink containing a Fc (II)-Fc (III) redox couple. [00073] The catalyst ink provided in accordance with the present disclosure containing a Fc (II)-Fc (III) redox couple acting as a radical scavenger helps increase the life of membrane drastically.

[00074] The catalyst ink provided in accordance with the present disclosure containing a Fc (II)-Fc (III) redox couple as a radical scavenger can help improve in the proton transport properties of the polymer electrolyte membrane when coated with said catalyst ink.

[00075] The process for preparing a catalyst ink containing a ferricyanide-ferrocyanide redox couple of the present disclosure is a simple process without requiring additional process steps like pre-processing or the like.

EXAMPLES

[00076] The disclosure will now be illustrated with working examples, which are intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary.

Example 1

Preparation of catalyst ink containing a Fc (II)-Fc (III) redox couple

[00077] Catalyst ink containing the Fc (II)-Fc (III) redox couple was prepared using following compositionsas per Table 1 and the process mentioned below:

(i) Compositions:

Table 1: Compositions for catalyst ink

* IP A: Isoprop ano

** EG: Ethylene glycol

(ii) Process for preparing the catalyst ink:

[00078] The catalyst ink was prepared by adding catalyst and potassium ferrocyanide or potassium ferricyanide to solvent system and mixing and adding ionomer and further mixing.

To determine the content of the components of the composition, carbon supported Pt catalyst content was taken as reference. The content of ionomer was decided on the basis of weight of carbon present in the catalyst and content of potassium ferrocyanide or potassium ferricyanide was decided on the basis of these catalyst and ionomer weight. For example, to have catalyst ink C3, 2 wt% (based on total solid content of catalyst, ferrocyanide and ionomer) of potassium ferrocyanide was taken along with the 50 wt% Pt coated catalyst and added to DI water. Physical dispersion of the powder materials in DI water was carried out. After that isopropanol and glycerol were added by taking in 1 : 1 ratio, while keeping water to organic solvent (mixture of isopropanol and glycerol) ratio 1 :2. Again physical mixing was carried out and ionomer was added by maintaining the ionomer to carbon ratio of 3:5. After addition of ionomer probe sonication was done for 2 minutes, followed by 20 minutes of sonication in sonication bath. Thus, obtained catalyst ink was used for coating the membrane to get the catalyst coated membrane.

Example 2

Process for providing Membrane Coated with Catalyst Ink of Composition C8

[00079] The PFSA membrane were coated with the catalyst ink C8 prepared in Example 1. The coating was performed by a decal -transfer method. Catalyst ink was coated on the PTFE sheets and dried on hot plate while keeping the temperature 100°C. The process was repeated until the desired Ptloading was reached, to 0.3 mg/cm² for the cathode application. The catalyst layer was then transferred to the PFSA membrane by hot press through maintaining the temperature of hot press in the range of 130°C and pressure in the range of 80 bar for 5 minutes. After that the system was cool down the PTFE sheet was peeled off the catalyst ink coated membrane.

[00080] The same process can be used for both anode and cathode side, but one side was directly coated on the membrane and other was transferred on membrane by decal transfer method, while maintaining the Pt loadings. For anode side the desired Pt loading was 0.1 mg/ cm².

Example 3

Coating of Membrane with Catalyst Ink of Composition C3 to provide Catalyst Coated Membrane

[00081] The PFSA membrane was coated with the catalyst ink C3 prepared in Example 1. The coating was performed by a decal -transfer method. Catalyst ink was coated on the PTFE sheets and dried on hot plate while keeping the temperature 80°C. The process was repeated until the desired Pt loading was reached, which was 0.3 mg/cm² for the cathode application. The catalyst layer was then transferred to the PFSA membrane by hot press through maintaining the temperature of hot press in the range of 120°C and pressure in the range of 100 bar for 3 minutes. After that the system was cool down the PTFE sheet was peeled off the catalyst ink coated membrane.

[00082] The same process can be used for both anode and cathode side, but one side was directly coated on the membrane and other was transferred on membrane by decal transfer method, while maintaining the required Pt loadings. For anode side the desired Pt loading was 0.1 mg/ cm². Example 4

Durability Test of Catalyst Coated Membrane

[00083] The durability test of the catalyst coated PSFA membrane of Example 3 that is the membrane coated with the catalyst ink C3 of the present invention as per Example 2 and for a comparison purpose of a conventional catalyst coated membrane wherein, ferrocyanide-ferricyanide is simply provided by physical or ligand exchange in electrolyte membrane was carried out by following the protocol laid by U.S. Department of Energy and all the parameters as can be found in the reference document “Hydrogen Storage Technologies Roadmap Fuel Cell Technical Team Roadmap November 2017”.

[00084] It was observed that PFSA membrane of Example 3 was stable for 1.5 times higher life cycle (<20% loss in OCV) than PSFA membrane coated with catalyst ink having no redox couple in both anode and cathode. The advantages of having Fc (II)-Fc (III) redox couple in catalyst ink is that, it is quite simple and does not require and chemical processing or does not involve any additional processing step. While the other existing technologies which have been used requires some kind of chemical pretreatment, extra layering or different steps making the process more time consuming at the same time resulting in extra cost of fabrication.

[00085] From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein merely for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention and should not be construed so as to limit the scope of the invention or the appended claims in any way.

Claims

We Claim:

1. A composition for catalyst ink containing ferricyanide-ferrocyanide redox couple, the composition comprising ferricyanide or ferrocyanide salt; perfluorosulfonic acid (PFSA) ionomer; platinum on carbon Pt/C catalyst; and a solvent system comprising water and organic solvent(s) selected from alcohol and polyol.

2. The composition as claimed in claim 1, wherein the ferricyanide or ferrocyanide salt is potassium salt.

3. The composition as claimed in claim 1, wherein the organic solvent is alcohol.

4. The composition as claimed in claim 1 or 3, wherein the alcohol is selected from Cl to C6 alcohol.

5. The composition as claimed in claim 1, wherein the polyol is selected from ethylene glycol, glycerol, and propanediol.

6. The composition as claimed in claim 1, wherein the potassium ferrocyanide or potassium ferricyanide is present in the composition from about 2% to about 20%, preferably in the range from about 2% to about 5% on w/w basis of the composition.

7. The composition as claimed in claim 1, wherein the Pt-C catalyst comprises Pt loading on carbon ranging from about 10% to about 70 wt% of carbon.

8. The composition as claimed in claim 1, wherein the ratio of PFSA ionomer to carbon is in the range from about 2:5 to about 1 : 1.

9. The composition as claimed in claim 1, wherein the ratio of carbon to a solvent system is in the range from about 1 :5 to about 1 :30.

10. The composition as claimed in claim 1, wherein the ratio of water to organic solvent(s) is in the range from about 1 : 1 to about 1 :5.

11. The composition as claimed in claim 1, wherein the ratio of alcohol to polyolis in the range from about 3 : 1 to about 1 :2.

12. A process for preparing a catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple, the process comprising: i) preparing catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple, the process comprising: a) mixing a catalyst with ferricyanide or ferrocyanide salt in a solvent system, b) adding ionomer in the mixture obtained in step (a) and mixing to obtain an ink, c) homogenizing the ink by a probe sonication, and d) homogenizing the ink in sonication bath to obtain the catalyst ink containing ferricyanide-ferrocyanide redox couple; and ii) coating a perfluorosulfonic acid (PF SA) membrane with the catalyst ink containing the (Fc (II)-Fc (III)) redox couple obtained in step (i) by steps comprising: a) coating the catalyst ink containing ferricyanide-ferrocyanide (Fc (II)-Fc (III)) redox couple on a polymeric film; b) drying the coated polymeric film in hot air at a temperature ranging from about 80°C to about 150°C; c) repeating steps (a) and (b) to achieved catalyst ink loading on the film; d) transferring the catalyst layer from the catalyst coated film to a perfluorosulfonic acid (PFSA) membrane by pressing a side of the film coated with the catalyst with the PSFA membrane in a hot press, maintaining the hot press at a temperature in the range of about 100°C to about 140°C and pressure in the range of about 60 bar to 130 bar for about 2 minutes to about 10 minutes to provide a catalyst coated membrane; and e) peeling off the film from the catalyst coated membrane.