Method for manufacturing a gas diffusion electrode, method for manufacturing a membrane electrode assembly for a fuel cell, and catalyst composition for a gas diffusion electrode

Abstract

The manufacturing method of a gas diffusion electrode (GDE) for an oxygen reduction reaction includes the following operation steps. a) Providing a particulate catalyst composition containing at least iron (Fe) at at least two different oxidation degrees, such as Fe and Fe2O3, and carbon (C), wherein the catalyst composition is obtained from frictional oxidation by the friction between a brake pad and a brake disk; b) Mixing the catalyst composition obtained in step a) with a liquid phase to obtain a catalyst mixture (10); c) Depositing the catalyst mixture (10) obtained in step b) on a backing sheet (11) and drying the catalyst mixture (10).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a gas diffusion electrode for an oxygen reduction reaction, a method for manufacturing a membrane electrode assembly for a fuel cell, and a catalyst composition for manufacturing a gas diffusion electrode.

Background Art

[0002] A fuel cell (hereinafter, FC) is a type of electrochemical device that can directly convert chemical energy into electrical energy with high efficiency. In particular, an FC can generate electric power from oxygen (O2) and hydrogen (H2) according to the reaction of 2H2 + O2 → current + 2H2O. Since water (H2O) is the only waste product of the fuel cell, automotive solutions based on this device are called zero-emission vehicles. In a fuel cell, by using an appropriate catalyst, the reaction between hydrogen and oxygen occurs in a controlled manner, avoiding combustion, and thus the generation of electrical energy is determined. Fuel cells that do not use hydrogen as fuel (for example, direct methanol fuel cells) and fuel cells that operate at high temperatures (for example, molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs)) are also known as prior art.

[0003] The operating principle of a fuel cell is based on two electrochemical half-reactions that occur in the anode and cathode compartments of the cell itself. The anode half-reaction is a hydrogen oxidation reaction, and the cathode half-reaction is an oxygen reduction reaction. Generally, the kinetics of the oxygen reduction reaction (ORR) is very slow and is the rate-determining step in the process. In order to effectively cause the latter reaction to generate electrical energy, it is necessary to promote it with an appropriate material, that is, a catalyst. The purpose of the catalyst is to reduce the energy barrier required for the activation of the process.

[0004] Typical catalysts for ORR are based on, for example, noble metal nanoparticles supported on mesoporous carbon.

[0005] Unfortunately, the use of noble metal-based electrode catalysts, which have limited supply and are not always readily available, is associated with their high cost and high demand for precious resources obtained from processes that typically have a large environmental impact. However, there are some examples of automotive applications where fuel cells, for example, exhibit a competitive advantage over batteries (see hydrogen vehicles). Specifically, with regard to automotive applications, polymer electrolyte fuel cells operating at low temperatures (usually 80 °C) are used. In this type of fuel cell, the anodic and cathodic half-reactions occur in half-cells separated by a thin polymer membrane (e.g., NAFION TM ). The polymer membrane serves as a physical barrier between the anode and cathode compartments and ensures appropriate ion conduction between the anode and cathode during operation of the device.

[0006] In a typical configuration of a polymer electrolyte fuel cell, the catalyst material is supported on two gas diffusion electrodes (GDEs) and pressed against an ion-conducting membrane. As a result, a three-layer structure of GDE (anode)-membrane-GDE (cathode) is formed. This assembly of the three-layer structure is called a membrane electrode assembly (MEA).

[0007] When referring specifically to polymer electrolyte fuel cells FCs, there are at least two categories. 1) Fuel cells that include a proton exchange membrane (hereinafter, PEMFC), 2) Fuel cells composed of an anion exchange membrane (AEMFC). In PEMFCs, the polymer electrolyte is a proton conductor (H + ions), whereas in AEMFCs the electrolyte is an anion conductor (hydroxyl OH - ions). This difference creates an acidic environment for the electrolyte in the former case and a basic environment in the latter case.

[0008] Electrode catalysts for ORR operating in an acidic environment (PEMFC) are typically based on platinum group metals (PGM). In contrast, catalysts for ORR operating under basic conditions (AEMFC) do not necessarily require PGM and are usually based on metals such as gold (Au), silver (Ag), nickel (Ni), etc.

[0009] Unfortunately, in any case (basic environment and acidic environment), the preparation of the ORR catalyst usually requires a long and energy-intensive synthesis procedure, including high-temperature pyrolysis treatment (up to 1000 °C). Furthermore, such procedures often also require the use of expensive reagents or precursors that are difficult to use on a large scale.

[0010] Furthermore, the need to employ particularly energy-intensive synthesis processes and the use of PGMs, on the one hand, require large amounts of resources (and strongly affect the final cost of the electrode catalyst), and on the other hand, strongly limit their effectiveness and production efficiency, thus virtually precluding the large-scale deployment of fuel cells for automotive applications.

[0011] Furthermore, the use of precious metals is also associated with significant environmental impacts due to their extraction.

[0012] Therefore, the need for an electrode catalyst and an electrode for an oxygen reduction reaction used in a fuel cell that can reduce energy consumption and resource utilization becomes immediately apparent.

[0013] A further need is for an electrode catalyst and an electrode for an oxygen reduction reaction used in a fuel cell that can reduce environmental impacts.

Summary of the Invention

[0014] The aforementioned needs are met by a method for manufacturing a gas diffusion electrode, a method for manufacturing a fuel cell membrane electrode assembly, a catalyst composition, and the use of a gas diffusion electrode according to the appended independent claims.

Brief Description of the Drawings

[0015] Further features and advantages of the present invention will become better understood from the description of the preferred embodiments given below as non-limiting examples.

Figure 1

Figure 2

Figure 2a

Figure 3

Figure 4

Figure 5

Figure 5a

Figure 6

Figure 7

Figure 8

[0016] Elements or parts of elements common to the embodiments described below are denoted by the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0017] In this specification, when a range of numerical percentages is indicated, unless otherwise specified, it is understood that both extremes of the range are always included.

[0018] Generally, in this specification, when expressions such as "free of precious metals" or "free of heavy metals" are used, it strictly means that such metals are completely absent, but also means when excluding a small amount of metals that may be present due to residues or impurities in the manufacturing process, and the amount is less than 1% by weight ratio.

[0019] Furthermore, unless otherwise specified in this specification, when referring to the content of a mixture, solution, or composition, it means the weight percentage relative to the total weight of the mixture, solution, or composition.

[0020] An example of the fuel cell FC1 according to the present invention is shown in FIG. 1.

[0021] According to an embodiment, the fuel cell FC1 includes a head plate 21 and a tail plate 22 on the opposite side where oxygen or hydrogen enters and exits the fuel cell FC1. The membrane electrode assembly (MEA) is interposed between the head plate 21 and the tail plate 22, and this MEA will be described in more detail in the latter half of this discussion.

[0022] In particular, FIG. 1 also shows an example of a fuel cell assembly 1 in which all the fuel cells FC1, FC2, FC3 are manufactured according to the present invention. Such a fuel cell assembly 1 includes a left end plate 2 and a right end plate 3 that include a stack of the fuel cells FC1, FC2, FC3 therebetween. Further, on each of the left 2 and right 3 end plates, preferably, electrodes 24, 34 are interposed for connection to an electric circuit for collecting the generated current, together with insulating layers 25, 35 that insulate the electrodes 24, 34 from the respective right 3 or left 2 plates.

[0023] The membrane electrode assemblies MEA of the fuel cells FC1, FC2, and FC3 according to the present invention include the gas diffusion electrodes (GDE) according to the present invention.

[0024] According to the present invention, a method for manufacturing a gas diffusion electrode (GDE) for an oxygen reduction reaction includes the following operating steps. a) Providing a particulate catalyst composition containing at least iron (Fe) in at least two different oxidation states, such as Fe and Fe2O3, and carbon (C). b) Combining the catalyst composition obtained in step a) with a liquid phase to obtain a catalyst mixture 10. c) Depositing the catalyst mixture 10 obtained in step b) on a backing sheet 11 and drying the catalyst mixture 10.

[0025] Advantageously, the catalyst composition provided in step a) is obtained from the frictional oxidation action due to the friction between a brake pad and a brake disk.

[0026] According to an advantageous structural modification, the catalyst composition according to the present invention is at least partially obtained from the frictional oxidation action due to the friction between a brake pad and a brake disk. However, it is clear that the present invention also relates to a catalyst composition having the composition itself shown in the embodiments described herein, regardless of the method by which such a composition is obtained.

[0027] Preferably, the brake disk is a cast iron disk, but the possibility of using a coated cast iron disk or a coated steel disk is not excluded.

[0028] Preferably, the cast iron disk is a fully pearlitic cast iron disk or a cast iron disk with a non-negligible ferrite content (for example, the ferrite content exceeds 5%).

[0029] Preferably, the cast iron disk is a cast iron disk of class I, A, 4-5 according to UNI EN ISO 945.

[0030] According to the embodiment, in the catalyst composition, iron (Fe) exists only as metallic iron (α-Fe) and magnetite (Fe3O4).

[0031] According to the embodiment, in the catalyst composition, iron (Fe) exists only as metallic iron (α-Fe) and hematite (Fe2O3).

[0032] According to the embodiment, in the catalyst composition, iron (Fe) exists only as magnetite (Fe3O4) and hematite (Fe2O3).

[0033] According to the embodiment, the particulate catalyst composition consists of metallic iron (α-Fe), hematite (Fe2O3), and magnetite (Fe3O4).

[0034] According to the embodiment, in the catalyst composition, iron (Fe) exists only as metallic iron (α-Fe), hematite (Fe2O3), and magnetite (Fe3O4).

[0035] According to the embodiment, the particulate catalyst composition also contains metallic zinc (Zn). In this modification, zinc helps to adjust the catalytic properties of the mixture.

[0036] According to one embodiment of the present method, in step c), the backing sheet 11 is a porous carbon sheet.

[0037] According to this embodiment, the liquid phase in step b) consists of a mixture comprising an ion-conductive ionomer, for example a polar solvent containing a sulfonated fluoropolymer and mesoporous carbon, for example a hydroalcoholic solution.

[0038] According to the embodiment, the particulate catalyst composition consists of at least 15% iron particles, at least 5% graphite (C), and a content of less than 40%, preferably less than 30%, of metallic zinc (Zn), and the remaining weight percentage of other constituents.

[0039] According to one embodiment in this specification, when the expression "other components" is used, such other components of the remaining weight percentage consist of or are composed of copper (Cu), tin (Sn), and optionally their oxides.

[0040] Preferably, at least 15% of such iron particles consist of at least 5% metallic iron (α-Fe) and at least 5% magnetite (Fe3O4).

[0041] Preferably, at least 15% of such iron metal particles consist of at least 5% metallic iron (α-Fe), at least 5% magnetite (Fe3O4), and at least 5% hematite (Fe2O3).

[0042] According to one embodiment, the particulate catalyst composition comprises 5% to 60% (including both ends) of metallic iron, 5% to 55% (including both ends) of magnetite, 5% to 40% (including both ends) of hematite, 5% to 40% (including both ends) of graphite, less than 40% of metallic zinc (Zn), preferably less than 30%, and the remaining weight percentage is composed of other components.

[0043] According to one embodiment, the particulate catalyst composition comprises 5% to 10% (including both ends) of metallic iron, 30% to 40% (including both ends) of hematite, 40% to 50% (including both ends) of magnetite, 5% to 10% (including both ends) of graphite, less than 5% of metallic zinc (Zn) (preferably less than 1%), and the remaining weight percentage is composed of other components.

[0044] According to the embodiment described in more detail in FIG. 8, for example, the particulate catalyst composition comprises 5% to 20% (including both end values) of metallic iron, 10% to 50% (including both end values) of magnetite, 5% to 35% (including both end values) of hematite, 5% to 20% (including both end values) of graphite, 1% to 25% (including both end values) of metallic zinc (Zn), and for the remaining weight percentage, one or more of the following components selected from the group consisting of copper, silicon carbide, zirconium oxide, and an alloy of copper and zinc.

[0045] According to an embodiment, the particulate catalyst composition comprises 5% to 20% (including both end values) of metallic iron, 10% to 50% (including both end values) of magnetite, 5% to 35% (including both end values) of hematite, 5% to 20% (including both end values) of graphite, 1% to 25% (including both end values) of metallic zinc (Zn), and for the remaining weight percentage, one or more components selected from the following components: 0.1% to 8% (including both end values) of copper, 0.1% to 15% (including both end values) of silicon carbide, 0.1% to 10% of zirconium oxide, 0.1% to 8% (including both end values) of an alloy of copper and zinc, and 0.1% to 5% (including both end values) of tin.

[0046] Preferably, before step a), the method includes step a', which includes collecting waste powder from the frictional oxidation of the brake pad in the direct vicinity of the brake pad and the brake disk, preferably a cast iron brake disk, by friction, thereby obtaining the particulate catalyst composition. This enables the use of a circular economy process in which unused waste becomes a material for the production of new components.

[0047] According to an embodiment, before step a), the method includes step a'' which includes treating waste powder resulting from the frictional oxidation of the brake pad and the brake disk (preferably made of cast iron) by friction through a filtration process and / or a grinding process and / or a washing process to obtain the particulate catalyst composition.

[0048] According to one aspect of the present invention, a method for manufacturing a membrane electrode assembly (MEA) for fuel cells FC1, FC2, and FC3 consists of the operation steps of the manufacturing methods of the gas diffusion electrodes GDE generally described in the above embodiments and in this discussion. Further, the method for manufacturing the membrane electrode assembly MEA includes the following operation steps, an example of which is shown in FIG. 2. - A step of joining the first side surface 111a of the polymer film 111 of the gas diffusion electrode GDE for oxygen reduction reaction to a backing sheet 11, which is, for example, a porous carbon sheet, to obtain the cathode side of the membrane electrode assembly (MEA). - A step of joining the second surface 111b of the polymer film 111 to the gas diffusion electrode GDEa for anodic half reaction on the side opposite to the first surface.

[0049] In this way, a membrane electrode assembly MEA is obtained in which the oxygen reduction half reaction electrode is obtained according to the method for manufacturing the gas diffusion electrode GDE of the present invention. The gas diffusion electrode GDEa for anodic half reaction can be obtained by techniques well known to those skilled in the art, for example, by drop casting, that is, depositing ink droplets on a substrate, or by a "doctor blade", that is, depositing ink on a substrate by a blade passing over the substrate at a predetermined distance.

[0050] According to one aspect of the present invention, a further method for manufacturing a membrane electrode assembly (MEA) for fuel cells FC1, FC2, and FC3 provides that the backing sheet 11 of the gas diffusion electrode GDE is a polymer film 111 instead of a porous carbon sheet. An example of the method is shown in FIG. 2a. That is, in addition to being composed of the operation steps of the manufacturing methods of the GDE gas diffusion electrodes described in the above embodiments and in this consideration, which are compatible with this embodiment, the method of this embodiment also includes the following operation steps. A step of joining the first side surface 11A of the backing sheet 11 of the gas diffusion electrode GDE for oxygen reduction reaction to a porous carbon sheet 110 to obtain the cathode side of the membrane - electrode assembly in which the backing sheet 11 of the gas diffusion electrode is a polymer film 111. Bonding the surface 11b of the backsheet 11, which is opposite to the first surface 11a, to the gas diffusion electrode GDEa for the anodic half-reaction.

[0051] In this modification, the catalyst composition is thus directly deposited on the polymer film 111 and then bonded to the porous carbon sheet 110.

[0052] Also in this modification, the electrode for the oxygen reduction half-reaction is obtained according to the method for manufacturing the gas diffusion electrode GDE of the present invention, while the gas diffusion electrode for the anodic half-reaction GDEa is obtained by techniques well known to those skilled in the art, examples of which have already been given in the previous paragraph.

[0053] It is also obvious that it is a further object of the present invention to fabricate fuel cells FC1, FC2, FC3 using the gas diffusion electrode GDE obtained according to the method described herein.

[0054] Furthermore, the present invention also relates to a particulate catalyst composition for the production of a gas diffusion electrode for an oxygen reduction reaction. Such a catalyst composition contains iron (Fe) and carbon (C) in at least two different oxidation states, and the catalyst composition is preferably obtained at least from the frictional oxidation action due to the friction of a brake pad against a brake disk made of cast iron.

[0055] It is obvious that using the catalyst composition described herein for the production of a gas diffusion electrode is a further object of the present invention.

[0056] Similarly, it is a further object of the present invention to use the gas diffusion electrode described herein for the production of a membrane electrode assembly (MEA) for fuel cells (FC1, FC2, FC3).

[0057] Furthermore, it is also a further object of the present invention to use the membrane electrode assembly (MEA) described herein for the production of fuel cells (FC1, FC2, FC3).

[0058] According to one embodiment, in the catalyst composition, iron (Fe) in at least two different oxidation states consists of at least metallic iron (Fe) (i.e., Fe(0) in the zero oxidation state) and hematite (Fe2O3) (i.e., Fe(III) in the +3 oxidation state).

[0059] According to an embodiment, in the catalyst composition, iron (Fe) in at least two different oxidation states consists of at least alpha - iron (α - Fe) and at least magnetite (Fe3O4) (i.e., Fe(II,III) in the +2 and +3 oxidation states).

[0060] According to an embodiment, in the catalyst composition, iron (Fe) in at least two different oxidation states consists of at least alpha - iron (α - Fe), at least hematite (Fe2O3) (i.e., Fe(III) in the +3 oxidation state), and at least magnetite (Fe3O4) (i.e., Fe(II,III) in the +2 and +3 oxidation states).

[0061] Furthermore, it is clear that the catalyst composition can be produced in any proportion combination of the compounds already described in the embodiments of the preceding paragraphs, with reference to the particulate catalyst composition described in the steps of the method for manufacturing a gas diffusion electrode.

[0062] According to one aspect, an advantageous general embodiment of the catalyst composition includes iron with at least two different degrees of oxidation (e.g., Fe and Fe2O3), carbon (C) in the form of graphite, and metallic zinc. The presence of at least the above four components provides excellent electrocatalytic performance, and even better performance is obtained when combined with the particle size of the powder mixture, as will be described later in this specification.

[0063] According to an embodiment, the catalyst composition consists of a powder mixture with an average particle size between 0.01 micrometers and 15 micrometers, preferably between 0.03 micrometers and 10 micrometers (including both extremes). Preferably, the powder consists of round - shaped particles with rounded edges.

[0064] According to an advantageous embodiment, the powder of the catalyst composition exhibits a bimodal dispersion of particle size, expressed as volume percentage, i.e., the size of the radius or the maximum chord length of each particle forming the powder. Preferably, the bimodal dispersion (or distribution) of the powder consists of a first peak between 0.2 and 0.4 micrometers, preferably 0.3 micrometers, and a second peak between 1 and 4 micrometers, preferably 3 micrometers. An example of such a bimodal dispersion is shown in FIG. 4.

[0065] In an advantageous aspect, the presence of a population of micrometer particles having a bimodal distribution (i.e., large particles surrounded by small particles) ensures an optimal packing of the particles themselves, along with a minimization of the free volume (i.e., the volume not occupied by the catalyst particles), as shown, for example, in FIG. 3. This state allows for the subsequent easy obtaining of a homogeneous catalyst layer with a high loading (understood as milligrams per square centimeter of catalyst composition) when fabricating a gas diffusion electrode (GDE).

[0066] With reference to both the method and the catalyst composition, the invention will be described in more detail below by means of several illustrative and non - limiting examples.

[0067] Example 1 As an example, the results obtained when using the powder released by a series of brake applications according to the WLTP - Brake Cycle (Worldwide - Harmonized Light vehicles Test Procedure for Brakes) as a catalyst are shown. It is reported in M. Mathissen et al., A novel Real - World Braking Cycle for Studying Brake Wear Emissions, Wear, 2018, 414 - 415, 219 - 226. Specifically, the disk brake configuration used consists of a friction material of the ECE R90 Low Steel type and a brake disk made of flake graphite cast iron with a fully pearlitic microstructure. The dust emitted during the WLTP brake test was used to obtain a gas diffusion electrode (GDE) according to the method described herein. Subsequently, the gas diffusion electrode GDE was tested by rotating disk electrode (hereinafter, RDE) voltammetry measurements, with the aim of evaluating its ability to catalyze the oxygen reduction reaction (O2 + 2H2O + 4e - →4OH - , E 0 = 1.230 V vs. RHE) in an alkaline environment.

[0068] The phase composition of the catalyst composition of this example is shown in Figure 5. The percentage values of the different phases were calculated by X - ray diffraction measurements followed by Rietveld analysis.

[0069] In this example, the catalyst composition consists of 8.1% metallic iron (Fe), 37.5% hematite (Fe >2 O >3 ), 47.1% magnetite (Fe >3 O4), 7.1% carbon (C), 0.15% iron sulfide (FeS), and trace amounts of zinc (Zn) (R wp = 6.38% and χ 2 = 3.38 as the balance factors obtained at the end of the Rietveld method analysis).

[0070] The catalytic activity of the catalyst composition of this example was investigated by rotating disk electrode (hereinafter, RDE) voltammetry measurements with reference to the oxygen reduction reaction. This was done by constructing a first rotating electrode (hereinafter, RDE1) containing an appropriate catalyst layer consisting of the catalyst composition described above. The RDE was immersed in an appropriate electrolyte at a) 25 ± 0.1 °C, rotated at b) 1600 rpm, and cycled at c) 20 mV / s in a saturated oxygen solution. After the voltammogram was stabilized, a scan was performed to increase the potential as shown in Figure 6. The obtained data was corrected for ohmic potential drop according to Van der Vliet et al., J. Electroanal. Chem. 647 (2010) 29 - 34. The Faraday current related to the oxygen reduction reaction was obtained by subtracting the voltammogram of the same RDE after cycling in a saturated argon electrolyte according to Jia X. Wang et al, Faraday Discuss. 140 (2008) 347 - 362.

[0071] Specifically, in this example, an appropriate catalyst layer of RDE1 was obtained by depositing an appropriate catalyst mixture 10 consisting of the catalyst composition on a glassy carbon disk electrode. The catalyst mixture 10 in the form of an ink consisted of the following composition. 10 mg of powder discharged from the brake (catalyst composition), 10 mg of mesoporous carbon (average particle diameter of graphite: 45 ± 5 μm, average pore diameter: 100 angstroms ± 10 angstroms), 12 μL of 5% Nafion TM aqueous solution, and 1 mL of water. The catalyst mixture 10 was sonicated for about 1 hour to uniformly disperse the ink components. Drops (15 μL) of the obtained catalyst mixture 10 were dropped onto a glassy graphite electrode and air-dried to obtain RDE1.

[0072] RDE1 was tested in a basic environment, using a 0.1 M KOH solution as the electrolyte. Specifically, cyclic voltammetry was performed in the potential range of -0.805 / +0.195 V with respect to Hg|HgO. The catalyst loading was 764 μg of powder per 1 cm 2 area.

[0073] The performance of the oxygen reduction reaction (ORR) was evaluated by comparing the electrode potential at a current of 100 μA. For reference, the ORR performance of a commercially available platinum catalyst composed of platinum nanoparticles supported on mesoporous carbon was measured. In this case, the catalyst mixture 10 consisting of the reference catalyst had the following composition. 1 mg of a commercially available EC20 catalyst (20% Pt on carbon), 12 μL of a 5% Nafion TM aqueous solution, and 1 mL of water. Drops (15 μL) of the resulting mixture were dropped onto a glassy carbon electrode and air-dried to obtain an RDE layer. The final platinum loading of the reference RDE layer was 15 μg Pt per 1 cm 2 area.

[0074] The comparison of the performance of the catalyst composition contained in RDE1 with that of the reference RDE is shown in FIG. 7.

[0075] Example 2 As an example, the results of using the powder released by a series of brake applications according to the WLTP-brake cycle (Worldwide-Harmonized Light Vehicles Test Procedure for Brakes) as a catalyst are shown. Specifically, the disk brake configuration used consisted of a copper-free type friction material of ECE R90 and a brake disk made of flake cast iron with a complete pearlite metal structure. The dust discharged during the WLTP braking test was used to obtain a gas diffusion electrode (GDE) according to the method described in the present invention. Next, the gas diffusion electrode was tested by rotating disk electrode (hereinafter, RDE) voltammetry measurement, and the ability to catalyze the oxygen reduction reaction (O2 + 2H2O + 4e - → 4OH - , E 0 = 1.230 V vs. RHE) in an alkaline environment was evaluated.

[0076] The phase composition of the catalyst composition of this example is shown in FIG. 5a. The percentage values of the different phases were calculated by X-ray diffraction measurement and subsequent Rietveld analysis.

[0077] In this example, the catalyst composition consists of 22.7% metallic iron (Fe), 15.8% hematite (Fe >2 O >3 ), 26.2% magnetite (Fe >3 O4), 11% carbon (C), and 24.3% metallic zinc (Zn).

[0078] The catalytic activity of the catalyst composition of this example was investigated by rotating disk electrode (hereinafter, RDE) voltammetry measurement with reference to the oxygen reduction reaction. This measurement was performed by constructing a second rotating electrode (hereinafter, RDE2) containing an appropriate catalyst layer composed of the catalyst composition described above using the same procedure as already described for Example 1 (RDE1).

[0079] The comparison of the performance of the catalyst composition contained in RDE2 with the performance of the reference RDE is shown in FIG. 7.

[0080] Example 3 As an example, the results obtained when using, as a catalyst, the powder released by a series of brake applications according to the WLTP - Brake Cycle (Worldwide - Harmonized Light Vehicles Test Procedure for Brakes) are shown. Specifically, the disk brake configuration used consisted of a high - performance friction material having a silicon resin binder and a brake disk made of flake - cast iron having a complete pearlite metal structure. The dust discharged during the WLTP braking test was used to obtain a gas diffusion electrode (GDE) according to the method described in the present invention. Next, the gas diffusion electrode was tested by rotating disk electrode (hereinafter, RDE) voltammetry measurement, with the aim of evaluating the ability to catalyze the oxygen reduction reaction (O2 + 2H2O+4e - →4OH - , E 0 = 1.230 V vs. RHE) in an alkaline environment.

[0081] The phase composition of the catalyst composition of this example is shown in FIG. 5a. The percentage values of the different phases were calculated by X - ray diffraction measurement and subsequent Rietveld analysis.

[0082] In this example, the catalyst composition consists of 54.2% metallic iron (Fe), 8.0% magnetite (Fe >3 O >4 ), 15.3% carbon (C), 7.9% zinc (Zn), 14.1% silicon carbide (SiC), and 0.5% tin (Sn).

[0083] The catalytic activity of the catalyst composition of this example was investigated by constructing a third rotating electrode (hereinafter, RDE3) composed of a suitable catalyst layer made of the previously described catalyst composition in the same procedure as already described for Example 1 (RDE1) by rotating disk electrode (hereinafter, RDE) voltammetry measurement with reference to the oxygen reduction reaction.

[0084] The comparison of the performance of the catalyst composition included in RDE3 with the reference RDE is shown in FIG. 7.

[0085] Example 4 As an example, the results obtained when the powder released by a series of brake applications according to the WLTP - brake cycle (Worldwide - Harmonized Light Vehicles Test Procedure fOr Brakes) was used as a catalyst are shown. Specifically, the disk brake configuration used consisted of an ECE R90 copper full - type friction material and a brake disk made of flake - cast iron with a complete pearlite metal structure. The powder discharged during the WLTP braking test was used to obtain a gas diffusion electrode (GDE) according to the method described in the present invention. Then, the gas diffusion electrode was tested by rotating disk electrode (hereinafter, RDE) voltammetry measurement for the purpose of evaluating its ability to catalyze the oxygen reduction reaction in an alkaline environment (O2+2H2O+4e - →4OH - , E 0 =1.230 V vs. RHE).

[0086] The phase composition of the catalyst composition of this example is shown in Figure 5a. The percentage values of the different phases were calculated by X-ray diffraction measurement and subsequent Rietveld analysis.

[0087] In this example, the catalyst composition consists of 11.4% metallic iron (Fe), 30.6% magnetite (Fe3O4), 19.2% hematite (Fe2O3), 16.6% carbon (C), 15% zinc (Zn), 16.6% copper (Cu), 4.1% copper-zinc alloy (Cu 0.7 Zn 0.3 Zn) 2.8%, and 0.3% metallic tin (Sn).

[0088] The catalytic activity of the catalyst composition of this example was investigated by rotating disk electrode (hereinafter, RDE) voltammetry measurement with reference to the oxygen reduction reaction, using the same procedure as already described for Example 1 (RDE1), by constructing a fourth rotating electrode (hereinafter, RDE4) including an appropriate catalyst layer made of the previously described catalyst composition.

[0089] The comparison of the performance of the catalyst composition included in RDE4 with the reference RDE is shown in Figure 7.

[0090] As can be understood from the foregoing description, the method for manufacturing a gas diffusion electrode, the method for manufacturing a fuel cell membrane electrode assembly, the catalyst composition, and the gas diffusion electrode each make it possible to overcome the drawbacks of the prior art.

[0091] In particular, the catalyst composition is obtained in an innovative way by frictional oxidation due to the friction between the brake pad and the brake disk following the braking process of an automobile.

[0092] In a particularly advantageous aspect, the method for manufacturing a gas diffusion electrode or the method for manufacturing a membrane electrode assembly does not include a pyrolysis step required in the prior art methods and is thus more energy-saving or more efficient.

[0093] Furthermore, the method according to the present invention does not require a step of preparing a porous structure of functionalized carbon, nor a step of infiltrating an iron-based precursor suitable for such a porous structure.

[0094] Furthermore, the method according to the present invention does not require the use of a template, such as graphene nanoplatelets or zeolite networks, which generally require particularly complex and time-consuming syntheses.

[0095] Furthermore, the method according to the present invention does not include a step of manufacturing or growing functionalized nanotubes (usually by chemical vapor deposition), which is generally very expensive and difficult to mass-produce.

[0096] In an innovative way, the gas diffusion electrode, membrane electrode assembly, and catalyst composition are based on abundant and inexpensive metals such as iron and zinc, and do not contain precious metals such as platinum, iridium, ruthenium, palladium, and heavy metals such as nickel, chromium, and lead, and are therefore very suitable for use as the cathode of a fuel cell.

[0097] In other words, the gas diffusion electrode or membrane electrode assembly or catalyst composition is preferably made to not contain platinum and / or iridium and / or ruthenium and / or palladium.

[0098] That is, the gas diffusion electrode or membrane electrode assembly or catalyst composition is preferably made to not contain heavy metals such as nickel and / or chromium and / or lead, and as a result, it brings an immediately beneficial effect to the environment.

[0099] Therefore, in a very advantageous way from the perspective of a circular economy, they enable the reuse of waste, i.e., particulate matter discharged by brakes, and enable the production of a catalyst that is effective, efficient, cost-effective, and environmentally friendly.

[0100] Furthermore, as a particularly advantageous method, the presence of graphite (C) in the catalyst composition, preferably homogeneously dispersed graphite (C), ensures excellent electrical contact between the metal particles and the oxide, thereby enabling efficient collection of electrons generated at electrocatalytically active sites.

[0101] Furthermore, the presence of secondary components of metals such as zinc or copper and tin advantageously enables the regulation of the properties of electrochemically active sites due to the oxygenophilicity and / or amphoteric nature of these elements.

[0102] In a particularly advantageous embodiment, the presence of iron makes the catalyst composition particularly suitable for catalyzing the oxygen reduction reaction (ORR) in a basic environment and suitable for use in an anion exchange polymer electrolyte fuel cell (AEMFC). Thus, it is itself the subject of the present invention.

[0103] Furthermore, the catalyst composition and the electrode according to the present invention do not contain platinum group metals (PGM), and problems associated with the cost and unavailability of precious metals do not occur either.

Claims

1. A method for producing a gas diffusion electrode (GDE) for an oxygen reduction reaction, comprising the following steps: a) A particulate catalyst composition comprising iron (Fe) and carbon (C) having at least two different degrees of oxidation is provided, wherein the catalyst composition is obtained from the frictional oxidation action due to friction between a brake pad and a brake disc. b) A step of mixing the catalyst composition obtained in step a) with a liquid phase to obtain a catalyst mixture (10), c) A method comprising the step of depositing the catalyst mixture (10) obtained in step b) onto a backing sheet (11) and drying the catalyst mixture (10).

2. The method according to claim 1, wherein in step c), the backing sheet (11) is a porous carbon sheet.

3. A method according to claim 1, wherein the liquid phase in step b) is composed of a mixture of a polar solvent comprising an ion-conducting ionomer and a mesoporous carbon.

4. A method according to claim 1, wherein the particulate catalyst composition comprises, by weight, at least 15% iron metal particles, at least 5% graphite, and less than 40%, preferably less than 30%, metallic zinc (Zn), with the remaining weight percentage consisting of other components.

5. A method according to claim 4, wherein the at least 15% iron-based metal particles comprise, by weight, at least 5% metallic iron (α-Fe) and at least 5% magnetite (Fe3O4).

6. The method according to claim 5, wherein the at least 15% iron-based metal particles are, by weight, at least 5% metallic iron (α-Fe), at least 5% magnetite (Fe3O4), and at least 5% hematite (Fe ２ O ３ Methods including )

7. The method according to claim 5, wherein the particulate catalyst composition comprises, by weight, 5% to 60% (including both values) of metallic iron, 5% to 55% (including both values), 5% to 40% (including both values), 5% to 20% (including both values), and less than 40% of metallic zinc (Zn), with the remaining weight percentage consisting of other components.

8. A method according to claim 7, wherein the particulate catalyst composition comprises, by weight, 5% to 10% (including both values) of metallic iron, 30% to 40% (including both values) of hematite, 40% to 50% (including both values) of magnetite, 5% to 10% (including both values) of graphite, and less than 5% of metallic zinc (Zn), with the remaining percentage consisting of other components.

9. A method according to claim 1, comprising step a' before step a), Step a' is a method for collecting waste powder generated from frictional oxidation due to friction between the brake pad and the brake disc in the immediate vicinity of the brake pad and / or the brake disc to obtain a particulate catalyst composition.

10. A method according to claim 1, comprising step a'') prior to step a) a) a filtration step and / or a grinding step and / or a washing step to obtain a particulate catalyst composition.

11. A method according to claim 1, the method comprising a step of thermal decomposition of the catalyst composition.

12. The operating steps for the method of manufacturing a gas diffusion electrode (GDE) according to claim 1, The operation step involves joining the first side surface (111a) of the polymer film to the backing sheet (11) of the gas diffusion electrode (GDE) for the oxygen reduction reaction to obtain the cathode side of the membrane electrode assembly (MEA), A method for manufacturing a membrane electrode assembly (MEA) for fuel cells (FC1, FC2, FC3), comprising the step of joining a second side (111b) of a polymer membrane (111) opposite to a first side (111a) to a gas diffusion electrode (GDE) for an oxygen reduction reaction.

13. The operating steps for the method of manufacturing a gas diffusion electrode (GDE) according to claim 1, A step of bonding the first side surface (11a) of the backing sheet (11) of the oxygen reduction reaction gas diffusion electrode (GDE) to a porous carbon sheet (110), thereby obtaining the cathode side of the membrane electrode assembly, wherein the backing sheet (11) of the gas diffusion electrode is a polymer film (111), A method for manufacturing a membrane electrode assembly (MEA) for a fuel cell (FC1, FC2, FC3), comprising the step of joining the surface (11b) of the backing sheet (11) opposite to the first surface (11a) to an anode half-reaction gas diffusion electrode (GDEa).

14. Use of a gas diffusion electrode obtained by the method of claim 1 in the manufacture of a fuel cell.

15. A particulate catalyst composition for the manufacture of a gas diffusion electrode for the oxidation reaction of oxygen, It contains iron (Fe) and carbon (C) having at least two different degrees of oxidation, A catalyst composition obtained by frictional oxidation due to friction between a brake pad and a brake disc.

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