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

Abstract

A particulate catalyst composition for manufacturing a gas diffusion electrode for an oxygen reduction reaction (ORR) comprises a catalyst composition containing at least iron (Fe) with at least two different degrees of oxidation, such as Fe and Fe₂O₃, and carbon (C). The gas diffusion electrode comprises the catalyst composition. A membrane electrode assembly (MEA) comprises a gas diffusion electrode (GDE).

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 accompanied by their high cost and high demand for precious resources obtained from processes that usually have a large impact on the environment. However, there are some examples of automotive applications where fuel cells, for example, exhibit a competitive advantage over batteries (see hydrogen vehicles). Particularly 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., NAFIONT TM ). The polymer membrane serves as a physical barrier between the anode and cathode compartments and ensures proper ion conduction between the anode and cathode during the 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 containing 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). 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 results in the former case creating an acidic environment for the electrolyte and the latter case creating a basic environment.

[0008] The electrode catalyst for ORR operating in an acidic environment (PEMFC) is usually based on platinum group metals (PGM). In contrast, the catalyst for ORR operating under basic conditions (AEMFC) does not necessarily require PGM and is usually based on metals such as gold (Au), silver (Ag), nickel (Ni), etc.

[0009] Unfortunately, in both cases (basic and acidic environments), the preparation of the ORR catalyst usually requires a long - time 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 adopt an energy - intensive synthesis process and the use of PGM, on the one hand, require a large amount of resources (and strongly affect the final cost of the electrode catalyst), and on the other hand, strongly limit its effectiveness and production efficiency, thus virtually hindering the large - scale deployment of fuel cells for automotive applications.

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

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

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

Summary of the Invention

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

Brief Description of the Drawings

[0015] Further features and advantages of the present invention will become more apparent from the following description of preferred embodiments, given by way of non-limiting example.

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 noble metals" or "free of heavy metals" are used, it strictly means that such metals are not present at all, 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 with respect 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 the 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 the 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 fuel cells FC1, FC2, FC3 are fabricated according to the present invention. Such a fuel cell assembly 1 includes a left end plate 2 and a right end plate 3 that sandwich a stack of fuel cells FC1, FC2, FC3 therebetween. Further, at each of the left 2 and right 3 end plates, electrodes 24, 34 are interposed for connection to an electrical circuit for collecting the generated current, preferably 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, FC3 according to the present invention include a gas diffusion electrode (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 comprising at least iron (Fe), for example Fe and Fe2O3, in at least two different oxidation states, as well as 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) onto 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 disc.

[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 disc. 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 disc is a cast iron disc, but the possibility of using a coated cast iron disc or a coated steel disc is not excluded.

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

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

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

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

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

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

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

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

[0036] According to an embodiment of the 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 of an ion-conductive ionomer, such as a sulfonated fluoropolymer, and a polar solvent containing mesoporous carbon, such as a hydroalcoholic solution.

[0038] According to an 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 herein, when the expression "other constituents" is used, such other constituents of the remaining weight percentage consist of or consist 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 an 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%, preferably less than 30%, of metallic zinc (Zn), 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 an embodiment described in more detail in FIG. 8, for example, the particulate catalyst composition comprises 5% to 20% (including both ends) of metallic iron, 10% to 50% (including both ends) of magnetite, 5% to 35% (including both ends) of hematite, 5% to 20% (including both ends) of graphite, 1% to 25% (including both ends) 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 one embodiment, the particulate catalyst composition comprises 5% to 20% (including both ends) of metallic iron, 10% to 50% (including both ends) of magnetite, 5% to 35% (including both ends) of hematite, 5% to 20% (including both ends) of graphite, 1% to 25% (including both ends) 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 ends) of copper, 0.1% to 15% (including both ends) of silicon carbide, 0.1% to 10% of zirconium oxide, 0.1% to 8% (including both ends) of an alloy of copper and zinc, 0.1% to 5% (including both ends) of tin.

[0046] Preferably, before step a), the method includes step a', which involves collecting waste powder from the frictional oxidation of the brake pad due to friction in the immediate vicinity of the brake pad and the brake disk, preferably a cast iron brake disk, thereby obtaining a 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 involves treating the waste powder resulting from the frictional oxidation due to the friction between the brake pad and the brake disk (preferably made of cast iron) to obtain a particulate catalyst composition, by means of a filtration process and / or a grinding process and / or a washing process.

[0048] According to one aspect of the present invention, the method for manufacturing a membrane electrode assembly MEA for fuel cells FC1, FC2, FC3 consists of the operating steps of each of the above embodiments and the method for manufacturing a gas diffusion electrode GDE generally described in this treatise. Further, the method for manufacturing a membrane electrode assembly MEA includes the following operating steps, an example of which is shown in FIG. 2. - A step of joining the first side 111a of the polymer membrane 111 of the gas diffusion electrode GDE for the 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 side 111b of the polymer membrane 111 to the gas diffusion electrode GDEa for the anodic half-reaction on the side opposite to the first side.

[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 a gas diffusion electrode GDE according to the present invention. The gas diffusion electrode GDEa for the anodic half-reaction can be obtained by techniques well known to those skilled in the art, for example, by drop casting, i.e., depositing ink droplets on a substrate, or by a "doctor blade", i.e., depositing ink on a substrate by passing a blade over the substrate at a predetermined distance.

[0050] According to one aspect of the present invention, a further manufacturing method of the 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 method of the GDE gas diffusion electrode described in each of the above embodiments and this consideration that 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 the oxygen reduction reaction to the 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 the polymer film 111. A step of joining the surface 11b on the side opposite to the first surface 11a of the back sheet 11 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 joined to the porous carbon sheet 110.

[0052] Also in this modification, the electrode for the oxygen reduction half reaction is obtained according to the manufacturing method of the gas diffusion electrode GDE according to 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, and examples thereof 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 the fuel cells FC1, FC2, and FC3 using the gas diffusion electrode GDE obtained according to the method described in this specification.

[0054] Furthermore, the present invention also relates to a particulate catalyst composition for the production of a gas diffusion electrode (GDE) 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, using the gas diffusion electrode described herein for the production of a membrane electrode assembly (MEA) for fuel cells (FC1, FC2, FC3) is a further object of the present invention.

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

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

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

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

[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 the gas diffusion electrode.

[0062] According to one aspect, an advantageous general embodiment of the catalyst composition comprises iron with at least two different degrees of oxidation (e.g., Fe and Fe₂O₃), carbon in the form of graphite (C), and metallic zinc. The presence of at least the above four components provides excellent electrocatalytic performance, and even more excellent 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 mixture of powders having 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 particles having rounded edges.

[0064] According to an advantageous embodiment, the powder of the catalyst composition exhibits a bimodal dispersion of particle size, expressed as a volume percentage, i.e., indicating the size of the radius or the length of the maximum chord 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 embodiment, the presence of a population of micrometer-sized particles having a bimodal distribution (i.e., large particles surrounded by small particles), as shown, for example, in FIG. 3, 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). 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 present 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 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. 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 consisted 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 metal structure. 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 for the purpose 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 FIG. 5. The percent values of the different phases were calculated by X-ray diffraction measurement and subsequent 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 measurement with reference to the oxygen reduction reaction. This was done by constructing a first rotating electrode (hereinafter, RDE1) containing an appropriate catalyst layer composed of the catalyst composition described above. The RDE was a) immersed in an appropriate electrolyte at 25 ± 0.1 °C, b) rotated at 1600 rpm, and c) cycled at 20 mV / s in a saturated oxygen solution. After the voltammogram was stabilized, a scan was performed to increase the potential as shown in FIG. 6. The obtained data was corrected for the 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] In particular, in this example, a suitable catalyst mixture 10 composed of a catalyst composition was deposited on a glassy carbon disk electrode to obtain the catalyst layer of RDE1. The catalyst mixture 10 in the form of an ink had 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 Å ± 10 Å), 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 the glassy graphite electrode and air-dried to obtain RDE1.

[0072] RDE1 was tested in a basic environment, using 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 .

[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 composed of the reference catalyst had the following composition: 1 mg of commercially available EC20 catalyst (20% Pt on carbon), 12 μL of 5% Nafion TM aqueous solution, and 1 mL of water. Drops (15 μL) of the obtained mixture were dropped onto the glassy graphite electrode and air-dried to obtain the RDE layer. The final platinum loading of the reference RDE layer was 15 μg Pt per 1 cm 2 .

[0074] The comparison of the performance of the catalyst composition contained in RDE1 and the performance of the reference RDE is shown in Figure 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 consists 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 emitted 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.

[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 carried out by constructing a second rotating electrode (hereinafter, RDE2) containing an appropriate catalyst layer consisting 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 that of the reference RDE is shown in Fig. 7.

[0080] Example 3 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. Specifically, the disk brake configuration used consists of a high - performance friction material with a silicon resin binder and a brake disk made of flake - cast iron with a complete pearlite metal structure. The dust emitted 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) was evaluated for the purpose of

[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 rotating disk electrode (hereinafter, RDE) voltammetry measurement with reference to the oxygen reduction reaction, in the same procedure as already described for Example 1 (RDE1), by constructing a third rotating electrode (hereinafter, RDE3) composed of a suitable catalyst layer consisting of the catalyst composition described above.

[0084] The performance of the catalyst composition included in RDE3 and its comparison with the reference RDE are shown in Figure 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. Subsequently, the gas diffusion electrode was tested by rotating disk electrode (hereinafter, RDE) voltammetry measurement for the purpose of evaluating the 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 is composed 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 ) 2.8%, and 0.3% metallic tin (Sn).

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

[0089] The performance of the catalyst composition contained in RDE4 and comparison with the reference RDE are shown in FIG. 7.

[0090] As is clear from the above description, the catalyst composition, gas diffusion electrode, fuel cell membrane electrode assembly, method for manufacturing a gas diffusion electrode, and method for manufacturing a fuel cell membrane electrode assembly 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 the frictional oxidation action due to the friction between the brake pad and the brake disk following the braking process of an automobile.

[0092] 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.

[0093] 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.

[0094] Furthermore, in a particularly advantageous aspect, the gas diffusion electrode or membrane electrode assembly or catalyst composition preferably does not contain heavy metals such as nickel and / or chromium and / or lead, which thereby brings an immediately beneficial effect on the environment.

[0095] Thus, in a very advantageous way from the perspective of circular economy, they enable the reuse of waste, i.e., the particulate matter discharged by the brakes, and enable the production of catalysts that are effective, efficient, cost-effective, and environmentally friendly.

[0096] Furthermore, as a particularly advantageous method, the presence of graphite (C) in the catalyst composition, preferably uniformly 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.

[0097] 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 properties of these elements.

[0098] 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.

[0099] Furthermore, the catalyst composition and electrode according to the present invention do not contain platinum group metals (PGM) and are not troubled by the related problems of the cost and availability associated with the use of precious metals.

[0100] Furthermore, in a particularly advantageous embodiment, the method for manufacturing a gas diffusion electrode or the method for manufacturing a membrane electrode assembly does not include the pyrolysis step required in the prior art methods, so the energy consumption is low and it is efficient.

[0101] Furthermore, the method according to the present invention does not require the step of preparing the porous structure of functionalized carbon nor the step of infiltrating an iron-based precursor suitable for such a porous structure.

[0102] Furthermore, in the method according to the present invention, there is no need to use a template, for example, a graphene nanoplatelet or a zeolite network which generally requires particularly complex and time-consuming synthesis.

[0103] Furthermore, the method according to the present invention does not include a step of manufacturing or growing functionalized nanotubes (usually manufactured by chemical vapor deposition), which are generally very expensive and difficult to mass-produce.

Claims

1. A particulate catalyst composition for the manufacture of a gas diffusion electrode for an oxygen reduction reaction (ORR), comprising at least two different oxidation states of iron (Fe) and carbon (C).

2. The catalyst composition according to claim 1, which is at least partially obtained from the frictional oxidation effect caused by the friction between the brake pad and the brake disc.

3. The catalyst composition according to claim 1, A catalyst composition comprising, by weight, at least 15% iron particles, at least 5% graphite, less than 40% metallic zinc (Zn), and the remaining weight percentage consisting of other components.

4. The catalyst composition according to claim 3, wherein the at least 15% of iron particles consist of at least 5% by weight of metallic iron (α-Fe) and at least 5% of magnetite (Fe ３ O ４ A catalyst composition containing )

5. The catalyst composition according to claim 4, wherein the at least 15% of iron particles are, by weight, at least 5% metallic iron (α-Fe) and at least 5% magnetite (Fe ３ O ４ ), and at least 5% hematite (Fe ２ O ３ A catalyst composition containing ).

6. The catalyst composition according to claim 4 comprises, by weight, 5% to 60% (including both values) of metallic iron, 5% to 55% (including both values) of magnetite, 5% to 40% (including both values) of hematite, 5% to 20% (including both values) of graphite, and less than 40% of metallic zinc (Zn), with the remaining percentage consisting of other components.

7. A catalyst composition according to claim 6, comprising, 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%, preferably less than 1%, of metallic zinc (Zn), with the remaining percentage consisting of other components.

8. The catalyst composition according to claim 6 comprises, by weight, 5% to 20% (including both values) of metallic iron, 10% to 50% (including both values) of magnetite, 5% to 35% (including both values) of hematite, 5% to 20% (including both values) of graphite, and 1% to 25% (including both values) of metallic zinc (Zn), with the remaining weight percentage being selected from the group consisting of one or more constituent elements of copper, silicon carbide, zirconium oxide, copper-zinc alloys, and tin.

9. The catalyst composition according to claim 6, wherein by weight, It contains 5% to 20% (including both ends) metallic iron, 10% to 50% (including both ends) magnetite, 5% to 35% (including both ends) hematite, 5% to 20% (including both ends) graphite, and 1% to 25% (including both ends) metallic zinc (Zn). The remaining percentage is comprised of one or more selected from 0.1% to 8% (including both values) of copper, 0.1% to 15% (including both values) of silicon carbide, 0.1% to 10% (including both values) of zirconium oxide, 0.1% to 8% (including both values) of copper-zinc alloy, and 0.1% to 5% (including both values) of tin, in a catalyst composition.

10. Use of the catalyst composition according to any one of claims 1 to 9 for the manufacture of a gas diffusion electrode.

11. A gas diffusion electrode (GDE) comprising the catalyst composition according to any one of claims 1 to 9.

12. Use of the gas diffusion electrode according to claim 11 for the manufacture of membrane electrode assemblies (MEAs) for fuel cells (FC1, FC2, FC3).

13. A membrane electrode assembly (MEA) comprising a gas diffusion electrode (GDE) as described in claim 11.

14. Use of the membrane electrode assembly (MEA) according to claim 13 in the manufacture of a fuel cell or fuel cell stack (FC1, FC2, FC3).

15. A method for manufacturing a gas diffusion electrode (GDE) for an oxygen reduction reaction, a) A step of providing a particulate catalyst composition comprising at least two different degrees of oxidation of iron (Fe) and carbon (C), wherein the catalyst composition is obtained from frictional oxidation 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 for producing a gas diffusion electrode (GDE) for an oxygen reduction reaction, comprising the steps of depositing the catalyst mixture (10) obtained in step b) onto a backing sheet (11) and drying the catalyst mixture (10).

16. A method for producing a gas diffusion electrode (GDE) for an oxygen reduction reaction according to claim 15, comprising step a' of collecting waste powder generated from frictional oxidation due to friction between a brake pad and a brake disc in the immediate vicinity of the brake pad and / or the brake disc, prior to step a), thereby obtaining a particulate catalyst composition.

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