Fuel cell electrocatalyst, membrane-electrode assembly, fuel cell and method for improving electrocatalyst stability and increasing fuel cell durability

Abstract

The present invention relates to a fuel cell electrocatalyst for use in the efficient, renewable and clean generation of energy. The present invention specifically discloses a fuel cell electrocatalyst with a coating comprising nanoparticles. It also relates to a membrane-electrode assembly and a fuel cell comprising said electrocatalyst. The present invention more specifically discloses a method for improving electrocatalyst stability and increasing fuel cell durability. The present invention pertains to the technical fields of materials science, electrochemistry, nanotechnology and renewable energy.

Description

Fuel cell electrocatalyst, membrane-electrode assembly, fuel cell and method for improving electrocatalyst stability and increasing fuel cell durability. Descriptive Report of Invention Patent Field of Invention

[0001] The present invention relates to a fuel cell electrocatalyst for use in generating energy efficiently, renewably, and cleanly. Specifically, the present invention discloses a fuel cell electrocatalyst with a coating comprising nanoparticles. It also relates to a membrane-electrode assembly and a fuel cell comprising said electrocatalyst. More specifically, the present invention discloses a method for improving the stability of the electrocatalyst and increasing the durability of a fuel cell. The present invention falls within the technical fields of materials science, electrochemistry, nanotechnology, and renewable energies. Background of the Invention

[0002] Currently, sustainable development is a socio-economic-environmental model directly related to economic growth in a way that guarantees social inclusion and environmental protection. In this context, clean technologies emerge, which are new industrial processes or modifications to existing processes aimed at reducing the consumption of raw materials, energy consumption, environmental impacts, and waste. This need creates opportunities for the development of new clean technologies for energy generation.

[0003] Particularly in the context of clean energy generation, one can cite fuel cells for generating electricity from hydrogen and Oxygen, with water as its only byproduct. Among the most common fuel cells are solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), and proton exchange membrane fuel cells (PEMFCs).

[0004] Additionally, nanotechnology is a rapidly expanding science and has generated much expectation due to the unusual properties of nanoparticles made from various materials. However, its large-scale use still faces multiple limitations, beginning with the unavailability of nanoparticle preparations with high concentration, purity, and precise particle size distribution.

[0005] In this sense, Brazil is the world's largest producer of Niobium (Nb). Brazilian Nb reserves represent 98.4% of world reserves (ANM, 2020; Ministry of Mines and Energy, 2019). The applications of this element are diverse, ranging from its use in steel, the automotive industry, and shipbuilding; to its use in the development of optoelectronic components. Therefore, the development of technologies that add value to this metal, abundant in Brazilian territory, is of great interest to the country.

[0006] In the search for the state of the art in scientific and patent literature, the following documents related to the topic were found:

[0007] Patent application WO2022036427, with inventors in common with the present invention, discloses a niobium nanoparticle preparation obtained by a top-down approach. This preparation also exhibits the following technical characteristics: particles entirely within the nanometer granulometric range; high purity; industrial-scale production with a cost suitable for economic viability. The nanometric powder preparation has high purity, since the process does not add impurities or lead to the formation of reaction products, as is the case with state-of-the-art bottom-up (or synthesis) processes. On the other hand, WO2022036427 does not describe fuel cells such as those described in the present invention.

[0008] Thus, based on the literature reviewed, no documents were found that anticipated or suggested the teachings of the present invention, so the solution proposed here has novelty and inventive activity compared to the state of the art.

[0009] Specifically related to proton exchange membrane fuel cells (PEMFCs), the presence of catalysts that enable the redox reactions of the cell, also called electrocatalysts, is fundamental. A particular problem related to electrocatalysts is the dissolution of the metals that make up the electrodes, resulting in a loss of efficiency and durability of the fuel cell.

[0010] In view of the above, it is clear that the search for renewable, accessible and clean energy sources and the improvement of existing technologies is a constant necessity, since the generation of energy through conventional means, such as the combustion of biodiesel, methanol, natural gas and liquefied petroleum gas, entails several harmful environmental and socioeconomic effects. Summary of the Invention

[0011] Thus, the present invention solves the problems of the prior art by providing an electrocatalyst with a coating comprising a mass quantity of niobium, tantalum, titanium nanoparticles, or combinations thereof. Said electrocatalyst is capable of increasing the durability of fuel cells, improving and enabling more efficient and cleaner energy generation.

[0012] Additionally, the inventors surprisingly found that niobium nanoparticles comprising a significant degree of dampening in the electrocatalyst coating show more impressive results in improving electrocatalyst stability and increasing fuel cell durability.

[0013] Due to the significant niobium reserves in Brazilian territory, it is a The advantage of the present invention is to use this element for the production of electrocatalyst coatings.

[0014] In a first aspect, the present invention presents a fuel cell electrocatalyst comprising - Carbon-based support; - Platinum-based particle; and - coating comprising a mass quantity of niobium, tantalum, titanium nanoparticles or combinations thereof.

[0015] In a second aspect, the present invention provides a membrane-electrode assembly comprising - at least one anode or cathode comprising an electrocatalyst as defined above; and - at least one membrane permeable to ions.

[0016] In a third aspect, the present invention provides a fuel cell comprising the membrane-electrode assembly as defined above.

[0017] In a fourth aspect, the present invention provides a method for improving the stability of the electrocatalyst and increasing the durability of the fuel cell comprising at least one step of coating the electrocatalyst with a coating layer comprising a mass amount of Niobium, Tantalum, Titanium nanoparticles or combinations thereof.

[0018] These and other objects of the invention will be immediately appreciated by those skilled in the art and will be described in detail below. Brief Description of the Figures

[0019] The following figures are presented:

[0020] Figure 1 shows a schematic of an electrocatalyst of a non-limiting embodiment of the present invention.

[0021] Figure 2 illustrates the loss of electrochemically active area (ECSA) of Ultra-thin film electrodes containing PtsCo / CB (baseline) and Nb2Os / Pt3Co / CB catalysts when subjected to potential cycling between -0.2 and 1.8 V vs. RHE. Electrolyte: 0.5 M H2SO4 (no purge). Data collected and recorded at 100 mV.s⁻¹. 1 .

[0022] Figure 3 illustrates the loss of electrochemically active area (ECSA) of thin-film electrodes containing PtsCo / CB catalysts modified with 0.25 and 0.50 wt% Nb2O5 when subjected to potential cycles between 0.6 and 1.0 V vs. RHE. Electrolyte: 0.5 M H2SO4 (no purge). Data collected and recorded at 500 mV.s⁻¹. 1 . Detailed Description of the Invention

[0023] The present invention relates to an electrocatalyst with a coating comprising a mass quantity of niobium, tantalum, titanium nanoparticles or combinations thereof. Said coated electrocatalyst is capable of increasing the durability of fuel cells, improving and enabling more efficient and cleaner energy generation.

[0024] In the context of the present invention, the term "Niobium nanoparticle" encompasses various chemical entities containing Niobium, including metallic Niobium, oxides, hydrates, hydrides, carbides, or nitrides of Niobium, iron Niobium or Niobium alloyed with other metals or transition metals, or combinations thereof. It also includes NbO, NbC, Nb2O5, niobic acid, Niobium oxalate, FeNb, or combinations thereof.

[0025] Due to the significant niobium reserves in Brazilian territory, it is an advantage of the present invention to use this element for the production of improved electrocatalysts.

[0026] In the context of the present invention, the term "tantalum nanoparticle" encompasses various tantalum-containing chemical entities, including tantalum metal, tantalum oxides, hydrates, hydrides, carbides, or nitrides, tantalum iron or tantalum alloyed with other metals or transition metals, or combinations thereof. It also includes tantalum pentoxide.

[0027] In the context of the present invention, the expression "titanium nanoparticle" encompasses various titanium-containing chemical entities, such as a titanium oxide selected from the group consisting of TiO, TiO2 (rutile, anatase and / or brookite), Ti2O3, TisO, Ti2O, Ti3O5, Ti4O7, Ti5O9 and combinations thereof.

[0028] Additionally, the inventors surprisingly found that niobium nanoparticles comprising a significant degree of dampening in the electrocatalyst coating show more impressive results in improving electrocatalyst stability and increasing fuel cell durability.

[0029] In the context of the present invention, the expression "degree of amortization" should be understood as the extent to which a material exhibits a predominantly disordered phase, in contrast to predominantly monocrystalline and polycrystalline phases. "Amortization" can be understood as a process of loss of long-range order of atoms, molecules or ions in the crystalline structure of a given material, and may also exhibit short-range order.

[0030] In a first aspect, the present invention presents a fuel cell electrocatalyst comprising - Carbon-based support; - Platinum-based particle; and - coating comprising a mass quantity of niobium, tantalum, titanium nanoparticles or combinations thereof.

[0031] In one embodiment of the electrocatalyst, the carbon-based support is composed of carbon black, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers, or combinations thereof.

[0032] In one embodiment of the electrocatalyst, the platinum-based particle is composed of platinum and cobalt, platinum and iron, platinum and nickel, platinum and rhodium, platinum and palladium, or combinations thereof. In another embodiment, the platinum-based particle is composed of PtsCo.

[0033] In one embodiment of the electrocatalyst, the coating comprises a mass amount of niobium nanoparticles, wherein said mass amount is equal to or less than 1.0% by mass.

[0034] In one embodiment of the electrocatalyst, the niobium nanoparticles are composed of niobium pentoxide.

[0035] In one embodiment, the aforementioned mass quantity was 0.25% by mass. In another embodiment, the aforementioned mass quantity was between 0.2% and 0.8% by mass. In yet another embodiment, the aforementioned mass quantity was between 0.05% and 0.2% by mass.

[0036] In one embodiment of the electrocatalyst, the coating comprises a mass quantity of Nb2Ü5 nanoparticles comprising a significant degree of damping. In one embodiment, said particles have a degree of damping of at least 19%.

[0037] In one embodiment, the said mass quantity of particles preferably comprises an amortization rate of at least 20%, more preferably at least 25%, more preferably at least 30%, more preferably at least 35%, more preferably at least 39%, more preferably at least 40%, more preferably at least 45%, more preferably at least 50%, more preferably an amortization rate of at least 55%, more preferably at least 60%, more preferably at least 65%, and even more preferably an amortization rate of at least 70%. In one embodiment, the amortization rate is at least 71%, more preferably at least 72%, more preferably at least 73%. In a non-limiting embodiment, the amortization rate is 74%.

[0038] In one embodiment, the said mass quantity of particles preferably comprises an amortization rate of at least 39%, preferably an amortization rate of at least 55%, and even more preferably an amortization rate of at least 70%.

[0039] In one embodiment, the aforementioned mass quantity of Niobium pentoxide nanoparticles have an average size distribution of 150 nm. In one embodiment, said niobium nanoparticles comprise a particle size distribution profile that is: d10: between 14 and 110 nm; d50: between 29 and 243 nm; and d90: between 89 and 747 nm.

[0040] In a second aspect, the present invention provides a membrane-electrode assembly comprising - at least one anode or cathode comprising an electrocatalyst as defined above; and - at least one membrane permeable to ions.

[0041] In one embodiment of the membrane-electrode assembly, the membrane is composed of Nafion.

[0042] In a third aspect, the present invention provides a fuel cell comprising the membrane-electrode assembly as defined above.

[0043] In one embodiment of the fuel cell, said cell is of the proton exchange membrane fuel cell (PEMFC) type.

[0044] In a fourth aspect, the present invention provides a method for improving the stability of the electrocatalyst and increasing the durability of the fuel cell comprising at least one step of coating the electrocatalyst with a coating layer comprising a mass amount of Niobium, Tantalum, Titanium nanoparticles or combinations thereof.

[0045] The inventors surprisingly found that the protective coating of Nb2Ü5 nanoparticles on the PtsCo / C catalyst acts as a barrier to cobalt leaching, minimizing the loss of structural stability due to cobalt dissolution in commercial catalysts.

[0046] Furthermore, a uniform coating of the catalysts isolates them from the effects of contamination by additives in the paint formulations, resulting in improvements. Corrosion resistance is also increased with the use of the coating. Examples

[0047] The examples shown here are intended only to illustrate one of the numerous ways of carrying out the invention, without, however, limiting its scope. Example 1 - Preparation of niobium pentoxide nanoparticles

[0048] The nanoparticles were obtained through a milling process, resulting in particles with an average size distribution of around 150 nm. More details about this process can be found in document WO2022 / 036427, issued by FRAS-LE SA.

[0049] A Labstar LS01 stirred ball mill (Netzsch) was fed with micrometric particles of niobium pentoxide. The process involved high-energy wet milling. The particle suspension was 17.7 wt%, consisting of approximately 3500 g of milli-Q water + 10 M NaOH and 750 g of the solid sample, which was prepared and stabilized in the mill's mixing tank at pH 9 and titrated with 10 M NaOH. The milling spheres used were yttria-stabilized zirconia, 400 µm in diameter. The milling chamber was filled to 80% vol. and the suspension temperature was below 40 °C. The mill rotation speed was set to 3000 rpm and milling was conducted for 8 hours. To stabilize the suspension at pH 9, 10 M NaOH was added during milling, with samplings taken periodically and particle sizes measured.

[0050] In this example, several embodiments of niobium pentoxide nanoparticle preparations were obtained, with a purity greater than 99%. Commercial niobium pentoxide, with the particle size distribution described in Table 1, was pre-milled in a high-energy mill containing yttria-stabilized zirconia beads with a diameter of 400 µm, in liquid medium, and the pH adjusted to 6.6. The mill rotation speed was 3500 rpm, and the particle grinding was conducted at a temperature below 40 °C. Table 4 shows the particle size distribution (PSD) of niobium pentoxide. input (commercial product) and output of a pre-comminution stage.

[0051] Table 1 - Input DTP (commercial product) and output DTP after pre-comminution.

[0052] The average specific surface area S (m 2 The mass of the particles after the pre-comminution step was 0.32 m / g. 2 / g.

[0053] In one embodiment, the pre-comminuted particles were then fed into a high-energy mill, where conditions similar to those described above were applied, but with 200 µm Zr spheres and milled for different times, until each nanoparticle preparation was obtained. Three different nanoparticle preparations were obtained, each with a defined particle size distribution as described in Table 2.

[0054] Table 2 - Particle size distribution of three different preparations (C, D and E) of niobium pentoxide nanoparticles.

[0055] In the context of the present invention, particles obtained after 12 hours of grinding were used. Without wishing to be bound by theory, it is understood that samples exhibiting a higher degree of amortization contribute to the surprising effects presented. Example 2 - Electrocatalyst Production

[0056] Particles of a PtsCo / C electrocatalyst were coated with a coating layer comprising niobium pentoxide nanoparticles, using techniques such as colloidal processing routes, atomic layer deposition, and CVD.

[0057] In the present invention, the Nb2Ü5 nanometric layer was formed by liquid-phase chemical impregnation of amorphous Nb2Ü5 nanoparticles onto PtsCo particles previously dispersed in carbon black (CB). This process is sensitive to the pH of the dispersion, and the microstructure of the coating - including distribution and thickness - is controlled by the amount of Nb2Ü5 added and the reaction time.

[0058] The pH used for the adsorption of nanoparticles onto the surface of the catalytic particles is approximately 4.0. This value proved ideal for promoting electrostatic attraction between the catalytic materials and the Nb2Os nanoparticles, as well as preventing flocculation of the materials.

[0059] The present invention utilizes porous thin-layer electrodes with a specific structure (PTFE cylinder containing a concentric cylinder of glassy carbon), which allows for the controlled deposition of catalysts in dispersion, an approach more compatible with subsequent application in fuel cells.

[0060] In the present invention, quantities of niobium pentoxide equal to or less than 1.0% by mass were tested. In one embodiment, 0.25% by mass was used. In another embodiment, Nb2U5 deposition concentrations in the range of 0.2 to 0.8% by mass were evaluated. In yet another embodiment, Nb2U5 deposition concentrations in the range of 0.05 to 0.2% by mass were evaluated.

[0061] The electrocatalyst produced was characterized and applied in a proton exchange membrane fuel cell (PEMFC). Example 3 - Comparative study of electrochemically active area loss (ECSA) of electrodes containing Nb oxide.

[0062] A fuel cell with the electrocatalyst of the present invention in operation was compared to a fuel cell with a prior art electrocatalyst.

[0063] For reference, Table 1 presents a comparative result of electrochemically active area loss (ECSA) of a sample with 0.25% by mass (nominal) of niobium pentoxide, obtained from an accelerated degradation electrochemical test that aimed to simulate the most critical stress cycle in a fuel cell for automotive application. 1 RHE: reversible hydrogen electrode 2 ECSA: electrochemically active surface area 3 CB: carbon black 4ALD: Atomic layer deposition, a subclass of chemical vapor deposition (CVD) 5 and: not available 6 CNTs: carbon nanotubes

[0065] The electrocatalyst of the present invention, with a coating comprising niobium pentoxide nanoparticles, maintained its structural stability and, consequently, its electroactivity under cycling.

[0066] Without wishing to be bound by theory, the inventors understood that the protective coating of Nb2Ü5 nanoparticles on the PtsCo / C catalyst acts as a barrier to cobalt leaching, minimizing the loss of structural stability due to cobalt dissolution in commercial catalysts.

[0067] Furthermore, a uniform coating of the catalysts isolates them from the effects of contamination by additives in the paint formulations, resulting in improvements. Corrosion resistance is increased with the use of the coating.

[0068] There was an improvement in electrochemical stability as the coating technology used was applied to future operation in hydrogen / oxygen fuel cells. Example 4 - Electrochemical stability study

[0069] An experimental study conducted by the inventors demonstrated that one of the glassy carbon (GC) electrodes, manufactured in an ultrathin layer configuration with a catalyst modified with approximately 0.1% by mass of Nb2Ü5 (measured concentration), exhibited greater electrochemical stability, with a 59% reduction in initial area after 220 potential cycles between -0.2 and 1.8 V vs. RHE (reversible hydrogen electrode). Although the absolute area was lower than that of the commercial standard, the commercial electrode showed a loss of approximately 75% of the area loss. electrochemically active (ECSA) under the same conditions, as can be seen in Figure 2.

[0070] The results shown in Figure 2 suggest a catalytic cyclability 1.6 times higher for the system containing Nb2Ü5 over PtsCo / CB.

[0071] Further experimental results are presented in Figure 3, which illustrates and compares the ECSA variation of samples containing 0.25 and 0.50% by mass (nominal contents) of Nb2Ü5, after electrochemical accelerated degradation tests. These tests were designed to simulate the most critical stress cycle that occurs in an automotive fuel cell.

[0072] Although the absolute area of ​​these samples was lower than that of the commercial standard (whose curve is not shown), it was observed that the electrode with 0.25 wt% of Nb2Ü5 showed, on average, a loss of about 7% of the initial ECSA, while the sample with 0.50 wt% of Nb2Ü5 demonstrated high cyclic stability, comparable to that of the best electrodes reported in the technical-scientific literature.

[0073] Example 5 - Electrocatalyst production processes

[0074] After evaluating the mass quantities in the previous examples, electrocatalyst production processes that allow for larger-scale production were tested.

[0075] To this end, different deposition methods were tested, namely methods most representative of continuous processes. Thus, different methods such as screen printing, slot-die coating, inkjet printing, flexography and rotogravure printing were tested, which allow control of the thickness, uniformity and adhesion of the active layer on different substrates.

[0076] Those skilled in the art will appreciate the knowledge presented here and will be able to reproduce the invention in the forms presented and in other variants and alternatives, covered by the scope of the following claims.

Claims

Claims 1. Fuel cell electrocatalyst characterized by comprising - Carbon-based support; - Platinum-based particle; and - coating comprising a mass quantity of niobium, tantalum, titanium nanoparticles or combinations thereof.

2. Fuel cell electrocatalyst according to claim 1 characterized in that the carbon-based support is composed of carbon black, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, carbon nanofibers or combinations thereof.

3. Fuel cell electrocatalyst according to claim 1 characterized in that the platinum-based particle is composed of PtsCo.

4. Fuel cell electrocatalyst according to claim 1 characterized in that the coating comprises a mass amount of niobium nanoparticles, wherein said mass amount is equal to or less than 1.0% by mass.

5. Fuel cell electrocatalyst according to claim 3 characterized in that the niobium nanoparticles are composed of niobium pentoxide.

6. Membrane-electrode assembly characterized by comprising - at least one anode or cathode comprising an electrocatalyst as defined in claim 1; and - at least one membrane permeable to ions.

7. Membrane-electrode assembly according to claim 6, characterized in that the membrane is composed of Nafion.

8. Fuel cell characterized by comprising the membrane-electrode assembly as defined in claim 6.

9. Fuel cell according to claim 8 characterized because it is a proton exchange membrane fuel cell (PEMFC).

10. Method for improving electrocatalyst stability and increasing fuel cell durability, characterized by comprising at least one step of coating the electrocatalyst with a coating layer comprising a bulk quantity of Niobium, Tantalum, Titanium nanoparticles or combinations thereof.

Images