Electrode, fuel cell, and their manufacturing method

Abstract

To provide an electrode using platinum which does not cause time degradation of an ion exchange membrane and which prevents and suppresses time degradation, such as output degradation caused by sulfur contained in hydrogen fuel or mixed from an environment, so-called sulfur poisoning, without additional equipment such as a filter, which directly increases cost.SOLUTION: An electrode includes platinum as at least part of its component, and at least a part of the platinum surface is modified with a substance that promotes oxidative decomposition of sulfur. The substances that promote oxidative decomposition of sulfur may include cerium salt or cerium metal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrode, a fuel cell, and a method for producing the same. [Background technology]

[0002] Fuel cells have been attracting attention as an energy source for mobility such as automobiles, buses, trucks, forklifts, trains, and ships, as well as for spacecraft, and as a stationary power source for homes and local governments.

[0003] Fuel cells generate electricity by using hydrogen fuel and oxygen from the atmosphere, with hydrogen oxidizing at the hydrogen electrode and oxygen reducing at the air electrode. Platinum catalysts are mainly used in the electrodes to efficiently promote the complex multi-electron transfer reactions of hydrogen oxidation and oxygen reduction.

[0004] Hydrogen, which is used as fuel, contains very small amounts of hydrogen sulfide during the manufacturing process or during storage and transportation. In hot spring areas and air-polluted areas, sulfur compounds are also present in the air, and they strongly adsorb to platinum catalysts, inhibiting (poisoning) the reaction, causing not only a drop in output but also long-term deterioration due to repeated poisoning and recovery. Therefore, when using fuel cells, such as in automobiles equipped with fuel cells, it is essential to have effective prevention and recovery technology against sulfur poisoning.

[0005] At the air electrode, there is an abundance of oxygen taken in from the atmosphere and it operates at a relatively high potential (+0.6 to +0.7 V) (all potentials are based on a silver / silver chloride reference electrode; the same applies below), making it easy for spontaneous recovery to occur through the oxidative decomposition of sulfur. On the other hand, at the hydrogen electrode operating at a low potential (around -0.2 V), spontaneous oxidative decomposition does not occur.

[0006] Currently, a method using a filter to remove sulfur is known as a technology for preventing and recovering from poisoning in the hydrogen electrode. However, the use of auxiliary equipment such as filters, which are preventive technologies against sulfur poisoning in the hydrogen electrode, or the improvement of the purity of hydrogen fuel leads to increased costs.

[0007] Another poisoning prevention and recovery technique is to use crossover oxygen to oxidize and decompose sulfur in the same way as the air electrode. Here, crossover oxygen refers to oxygen from the air electrode passing through the proton exchange membrane and reaching the hydrogen electrode, which is effective in promoting the oxidative decomposition and desorption of sulfur.

[0008] On the other hand, such crossover oxygen generates hydrogen peroxide and hydroxyl radicals in the platinum catalyst, which can cause deterioration of the proton exchange membrane. In order to solve these problems, it has become essential to take drastic measures, such as developing new catalyst materials that have activity comparable to that of platinum (Pt) and are highly resistant to sulfur poisoning. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication No. 2014-216157 [Patent Document 2] Patent Publication No. 2014-110152 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a platinum electrode, a fuel cell, and a method for manufacturing the same, which prevent or suppress deterioration over time, such as a decrease in output due to sulfur mixed in from the environment, or so-called sulfur poisoning, without requiring the installation of additional equipment such as a filter that directly increases costs and without causing deterioration over time of the ion exchange membrane on the hydrogen electrode side, and which do not cause deterioration over time. [Means for solving the problem]

[0011] The configuration of the present invention is shown below. (Configuration 1) Platinum is at least a part of the material of the electrode; An electrode, wherein at least a portion of the platinum surface is modified with a substance that promotes the oxidative decomposition of sulfur. (Configuration 2) 2. The electrode according to claim 1, wherein the substance that promotes the oxidative decomposition of sulfur is a cerium species selected from the group consisting of cerium salts and cerium metal. (Configuration 3) 3. The electrode according to claim 2, wherein a ratio of an area of ​​the platinum modified by the cerium species to a surface area of ​​the platinum is 1% or more and 50% or less. (Configuration 4) 4. The electrode according to claim 2 or 3, wherein the thickness of the cerium species modifying the platinum surface is 0.1 atomic layers or more and 10 atomic layers or less. (Configuration 5) 3. The electrode of claim 2, wherein the cerium salt is cerium nitrate. (Configuration 6) 6. The electrode of any one of claims 2 to 5, wherein the cerium valence in the cerium species is 3. (Configuration 7) 7. The electrode of any one of claims 1 to 6, wherein the platinum is in particulate form. (Configuration 8) 8. The electrode according to claim 7, wherein the diameter of the microparticles, as calculated by a spherical volume conversion method, is 1 nm or more and 10 nm or less. (Configuration 9) Preparing an electrode member having platinum as at least a part of its constituent material; immersing the electrode member in a solution containing one or more cerium species selected from the group consisting of cerium salts and cerium metal; and bubbling with hydrogen gas or holding at -0.2V; and drying the electrode. (Configuration 10) 10. The method for producing an electrode according to claim 9, wherein the solution is an aqueous solution containing cerium nitrate. (Configuration 11) 11. The method for producing an electrode according to claim 10, wherein the concentration of the cerium nitrate is 0.001 mol or more and 1 mol or less per 1 L of water that is a solvent for the aqueous solution. (Configuration 12) A fuel cell having at least a hydrogen electrode, an oxygen electrode, and an electrolyte, A fuel cell, wherein the hydrogen electrode comprises platinum as at least a part of its constituent material, and at least a part of the surface of the platinum is modified with a substance that promotes the oxidative decomposition of sulfur. (Configuration 13) 13. The fuel cell according to claim 12, wherein the substance that promotes the oxidative decomposition of sulfur is a cerium species that is one or more selected from the group consisting of cerium salts and cerium metal. (Configuration 14) 13. The fuel cell of claim 12, wherein the cerium salt is cerium nitrate. (Configuration 15) 14. The fuel cell according to claim 13, wherein the valence of cerium in the cerium species is 3. (Configuration 16) 16. The fuel cell of any one of aspects 12 to 15, wherein the platinum is in particulate form. (Configuration 17) Providing an oxygen electrode, an electrolyte, and a hydrogen electrode having platinum as at least a portion of its components; The hydrogen electrode and the oxygen electrode are disposed so as to face each other via the electrolyte, 12. A method for producing a fuel cell, wherein the hydrogen electrode is produced by the electrode production method according to any one of aspects 9 to 11. (Configuration 18) Providing an oxygen electrode, an electrolyte, and a hydrogen electrode having platinum as at least a portion of its components; disposing the hydrogen electrode and the oxygen electrode so as to face each other via the electrolyte; 17. A method for producing a fuel cell according to any one of claims 12 to 16, comprising adding a substance that promotes the oxidative decomposition of sulfur to the electrolyte. Effect of the Invention

[0012] According to the present invention, there are provided a platinum electrode, a fuel cell, and a method for manufacturing the same, which prevent or suppress deterioration over time, such as a decrease in output due to sulfur contained in hydrogen fuel or mixed in from the environment, without the need for additional equipment such as a filter that directly increases costs, and without causing deterioration over time of the ion exchange membrane on the hydrogen electrode side, so-called sulfur poisoning, as well as a method for manufacturing the same. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a fuel cell. [Diagram 2] An explanatory diagram explaining the reactions that occur at the electrodes of a fuel cell; (a) shows the hydrogen electrode and (b) shows the oxygen electrode. [Diagram 3] An explanatory diagram showing the reactions that occur at the hydrogen electrode of a fuel cell. (a) shows the case of sulfur poisoning, and (b) shows the case of platinum-52 being protected with cerium species. [Figure 4] FIG. 2 is a flow chart showing a method for producing an electrode according to the present invention. [Diagram 5] FIG. 2 is an explanatory diagram showing the configuration of a three-electrode beaker cell used in the present embodiment. [Figure 6] This is a characteristic diagram showing the relationship between the applied potential and the current, comparing a platinum electrode modified with Ce species with a bare platinum single crystal (111) electrode. [Figure 7] This is a characteristic diagram showing the relationship between the applied potential and the current, comparing a platinum single crystal (111) electrode with sulfur attached and a bare platinum electrode. [Figure 8] FIG. 1 is a characteristic diagram showing XPS spectra (S2p region) obtained before and after electrochemical measurement of a platinum single crystal (111) electrode modified with cerium species to which sulfur is adsorbed in an aqueous solution of 0.01 M cerium nitrate and 0.1 M perchloric acid. [Figure 9](a) shows the XAFS (X-ray Absorption Fine Structure) measurement data of a cerium-modified platinum single crystal (111) electrode sample that was treated in a 0.01M cerium nitrate + 0.1M perchloric acid aqueous solution that was bubbled with a mixed gas of argon and hydrogen for 1 hour under an open circuit potential (OCP) of -0.2V. (b) shows the XAFS measurement results of Ce(NO3)3 and CeO2. (c) shows the current-potential curve measurement results of the sample in (a). [Figure 10] This is a characteristic diagram showing the current-potential curves of a platinum single crystal (111) electrode that is not modified with cerium species and has sulfur adsorbed in an aqueous solution of 0.01 M cerium nitrate + 0.1 M perchloric acid, with the number of cycles as a parameter. [Figure 11] This is a characteristic diagram showing the current-potential curves of a platinum single crystal (111) electrode modified with cerium species to which sulfur is adsorbed in a 0.01M cerium nitrate + 0.1M perchloric acid aqueous solution, with the number of cycles as a parameter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Embodiment 1) In the first embodiment, a platinum electrode is described which prevents or suppresses deterioration over time, such as a decrease in output, caused by sulfur mixed in from the environment, so-called sulfur poisoning.

[0015] <Electrode structure> The platinum electrode of the first embodiment is characterized in that its surface is modified with a substance that promotes the oxidative decomposition of sulfur.

[0016] The platinum electrode of the first embodiment is intended for use in a hydrogen electrode where hydrogen is supplied as fuel. When using a hydrogen electrode, crossover oxygen is often introduced, but if a large amount of crossover oxygen is introduced into the hydrogen electrode, hydrogen peroxide and hydroxyl radicals are generated, as described in the background, which leads to deterioration of the proton exchange membrane.

[0017] The inventors of the present invention have found that by using a substance (promoter catalyst) that promotes the oxidative decomposition of sulfur added to the surface of the platinum electrode, sulfur adhesion and coating on the platinum electrode of the hydrogen electrode, that is, sulfur poisoning, can be suppressed by a normal potential cycle without introducing oxygen into the hydrogen electrode. Since no special oxygen introduction is required, deterioration of the proton exchange membrane is unlikely to occur. The potential cycle may be the hydrogen electrode operation during normal use of the fuel cell, i.e., -0.2V or more and +0.5V or less. Under these conditions of use, an electrode having platinum whose surface is modified with a substance that promotes the oxidative decomposition of sulfur becomes a hydrogen electrode that can prevent sulfur poisoning. In the case of platinum whose surface is not modified with a substance that promotes the oxidative decomposition of sulfur, a potential cycle of +0.7V to +1.0V is required for the oxidative decomposition of sulfur species, and under these conditions, hydrogen peroxide and hydroxyl radicals are generated, which causes deterioration of the proton exchange membrane. The platinum electrode of the first embodiment can also be used as an oxygen electrode placed in an oxygen-rich environment.

[0018] The substance that promotes the oxidative decomposition of sulfur can be exemplified by cerium species selected from the group consisting of cerium salts and cerium metal. Specifically, cerium metal (Ce), cerium nitrate (Ce(NO 3 ) 3 ), Cerium chloride (CeCl 3 ), cerium acetate (Ce(CH 3 COO) 3 ), cerium sulfate (Ce(SO 4 ) 2 ), and cerium hydroxide (Ce(OH) 3 ), and cerium nitrate (Ce(NO 3 ) 3 ) can be used preferably. Here, the valence of cerium as the cerium species is preferably 3, as shown in the examples described later, in view of its sulfur oxidative decomposition ability.

[0019] 2A and 2B are diagrams for explaining the state of electrodes having platinum particles 52 and 62 that are not poisoned by sulfur, where FIG. 2A shows a hydrogen electrode and FIG. 2B shows an oxygen electrode. Here, the platinum particles 52 and 62 are deposited on carbon 51 and 61. At the hydrogen electrode, hydrogen gas (H 2 ) is adsorbed to the platinum particles 52 as hydrogen atoms (H) 53, and hydrogen ions (H + )54 is generated. On the other hand, at the oxygen electrode, oxygen gas (O 2 ) is a hydrogen ion (H + ) reacts with water (H 2 O) is produced, and the water produced escapes to the outside.

[0020] However, at the hydrogen electrode, hydrogen sulfide (H 2 When sulfur compounds (sulfur species) such as sulfur (S) 55 are introduced, sulfur (S) 56 adheres to the surface of the platinum fine particles 52, and the sulfur compounds are converted into hydrogen gas (H 2 )57, i.e., hydrogen ion (H + ) is produced. And this hydrogen ion (H + ) generation is inhibited, thereby reducing power generation.

[0021] On the other hand, in the case of an electrode using platinum fine particles modified with cerium species according to the present invention, as shown in FIG. 3(b), sulfur species brought from the environment, etc., are oxidized and decomposed to SO by the catalytic action of cerium (Ce), especially trivalent cerium, which has a large catalytic action, even under a low applied potential. 2 (59) and released to the outside. 2 ) is adsorbed on the platinum particles 52 as hydrogen atoms (H), and converted into hydrogen ions (H + ) is generated.

[0022] The amount of modification with a substance that promotes the oxidative decomposition of sulfur can be, for example, in the case of cerium species, 1% to 50% of the platinum surface area covered, and 0.1 to 10 atomic layers, preferably 1 atomic layer, in terms of thickness. When the amount of modification with cerium species is within this range, platinum and cerium species act in concert to effectively remove sulfur. These amounts can be measured using a SEM (Scanning Electron Microscope) or a TEM (Transmission Electron Microscope).

[0023] The platinum electrode is not particularly limited as long as it is an electrode containing platinum (Pt), but platinum or a platinum-heterogeneous metal alloy is preferably used because of its high electrochemical action (catalysis) as a fuel cell electrode. The shape or form of the platinum or platinum-heterogeneous metal alloy catalyst is also not particularly limited, but it may be plate-like or fine particle-like. In the case of a plate-like shape, it is easy to form, and in the case of a fine particle-like shape, the surface area per unit amount is large, and the adsorption and reaction of hydrogen gas occurs efficiently. Platinum fine particles are preferably used as an electrode for a high-efficiency fuel cell. The size of the platinum fine particles is preferably 1 nm or more and 10 nm or less, expressed as the diameter when converted into a sphere by volume. If the platinum fine particles have a size in this range, the surface area per unit amount can be earned, and expensive platinum can be used efficiently. When platinum is used as fine particles, it is recommended to use carbon or the like as a carrier and a polymer electrolyte or the like as a binder.

[0024] <Electrode manufacturing method> The method for producing the electrode according to the first embodiment will be described with reference to the flow chart of FIG. First, an electrode member containing platinum as at least a part of its constituent material is prepared (step S11). Examples of electrode members containing platinum as at least a part of its constituent material include a platinum metal plate and a platinum microparticle-supported carbon electrode in which platinum microparticles are supported on a conductive carrier made of carbon or the like. Here, platinum may be an alloy with a transition metal such as iron, cobalt, or nickel, or a binder made of a polymer electrolyte or the like may be used.

[0025] Next, the electrode member is immersed in a solution containing cerium seeds, and is coated with cerium seeds by bubbling with hydrogen gas or by holding at −0.2 V (step S12). Here, the solution containing cerium species is preferably one in which cerium species are dissolved in water. The cerium species is one or more selected from the group consisting of cerium salts and cerium metal. Specific examples of cerium species include cerium metal, cerium nitrate, cerium chloride, cerium acetate, cerium sulfate, and cerium hydroxide. Cerium nitrate is particularly preferred because it is easy to handle and is a trivalent substance. When cerium nitrate is used as the cerium species, the concentration of the cerium species is preferably 0.001 mol or more per 1 L of water, which is the solvent of the aqueous solution. At this concentration, the platinum electrode can be modified with an amount of cerium species that can suppress sulfur poisoning. There is no particular upper limit to the concentration of the cerium species, but in consideration of the saturation of the effect and resource saving, 1 mol per 1 L of water can be mentioned.

[0026] Thereafter, the electrode is dried (step S13) to obtain a platinum electrode having a high sulfur poisoning prevention effect. Here, examples of the drying method include air drying, heating, and blowing with a gas.

[0027] (Embodiment 2) In the second embodiment, a fuel cell in which degradation over time, such as a decrease in output power, caused by sulfur mixed in from the environment, etc., is suppressed will be described.

[0028] <Structure and Features> As shown in FIG. 1, the fuel cell 101 of the second embodiment has a hydrogen electrode consisting of a hydrogen electrode 11 and a hydrogen electrode collector 12, an oxygen electrode consisting of an oxygen electrode 13 and an oxygen electrode collector 14, and an electrolyte 15. Here, the hydrogen electrode 11 is an electrode having platinum as at least a part of its constituent materials, and at least a part of the surface of the platinum is modified with a substance that promotes the oxidative decomposition of sulfur, i.e., the hydrogen electrode described in embodiment 1. As described in the first embodiment, the modifier for promoting the oxidative decomposition of sulfur in the hydrogen electrode 11 is preferably one or more cerium species selected from the group consisting of cerium salts and cerium metal. Specific examples of cerium species include cerium metal, cerium nitrate, cerium chloride, cerium acetate, cerium sulfate, and cerium hydroxide. In particular, cerium nitrate is preferably used because it is easy to handle and is a trivalent substance. Furthermore, the electrode having platinum as at least a part of its constituent materials, the hydrogen electrode 11, is not particularly limited as long as it is an electrode containing platinum, but platinum or a platinum-heterogeneous metal alloy is preferably used because of its high electrochemical action (catalytic action) as a fuel cell electrode. There is also no particular limit to the shape or form of the platinum or platinum-heterogeneous metal alloy catalyst, but it may be in the form of a plate or fine particles. In the case of a fine particle shape, the surface area per unit amount is large, and hydrogen gas is efficiently adsorbed and reacted, so platinum fine particles are preferably used as an electrode for a highly efficient fuel cell.

[0029] There are no particular limitations on the hydrogen electrode collector 12 as long as it is made of a conductive material, and examples of such materials include an electrode made of carbon and metal oxide.

[0030] On the other hand, the oxygen electrode 13 is not particularly limited, but may be an electrode made of a material consisting of platinum or a platinum-heterogeneous metal alloy, and the oxygen electrode collector 14 is not particularly limited, but may be an electrode made of a material consisting of carbon and a metal oxide.

[0031] The electrolyte 15 is not particularly limited, and examples thereof include an aqueous electrolyte solution and a solid polymer electrolyte. Among these, a solid polymer electrolyte such as a perfluorosulfonic acid membrane, such as Nafion (registered trademark) or Aquivion (registered trademark), is preferably used because it is a material that is widely used in actual solid polymer fuel cells.

[0032] In addition, cerium oxide (CeO x Patent Document 2 discloses that high performance can be achieved even in the medium temperature range (100-200°C) by using platinum nanoparticles and carbon particles partially covered on the surface with a cerium oxide layer. In this method, cerium oxide is used, but its function is to replace platinum with CeO at the oxygen electrode during the operation of the fuel cell. x The purpose of this is to suppress the oxidation of platinum by oxidizing and reducing platinum, thereby maintaining and bringing out the inherent performance of platinum over a wide operating range, and is completely different from the purpose, function, mechanism, and effect of oxidizing and decomposing sulfur at the hydrogen electrode of the present application.

[0033] When hydrogen gas is introduced into the hydrogen electrode 11 and oxygen gas is introduced into the oxygen electrode 13 , electricity is supplied to a load 17 such as a motor via wiring 16 .

[0034] As explained in the first embodiment, when an electrode in which platinum is at least a part of the constituent material and at least a part of the surface of the platinum is modified with a substance such as cerium nitrate that promotes the oxidative decomposition of sulfur is used as the hydrogen electrode 11, sulfur that is about to adhere to or has adhered to the electrode is oxidized and decomposed in a normal operation potential cycle, i.e., a potential cycle of -0.2 V or more and +0.5 V or less, and sulfur poisoning of the electrode is suppressed. This sulfur poisoning suppression is performed without supplying any particular oxygen gas to the hydrogen electrode side, so that deterioration of the proton exchange membrane is also suppressed. Therefore, the fuel cell 101 according to the second embodiment is a high-output, high-efficiency fuel cell with little deterioration over time.

[0035] <Manufacturing method> The fuel cell 101 of embodiment 2 comprises preparing a hydrogen electrode 11 having the aforementioned oxygen electrode 13, electrolyte 15, and platinum as at least some of its constituent materials, and arranging the hydrogen electrode 11 and the oxygen electrode 13 so as to face each other via the electrolyte 15 and housing them in a casing. The hydrogen electrode 11 can be manufactured using the electrode described in embodiment 1 or using an electrode manufactured by the electrode manufacturing method described in embodiment 1. Alternatively, the fuel cell 101 of embodiment 2 can be manufactured by preparing the aforementioned oxygen electrode 13, electrolyte 15, and hydrogen electrode 11 having platinum as at least some of its constituent materials, arranging the hydrogen electrode 11 and the oxygen electrode 13 so as to face each other via the electrolyte 15 and housing them in a casing, and adding a substance that promotes the oxidative decomposition of sulfur to the electrolyte 15. Here, the substance that accelerates the oxidative decomposition of sulfur is preferably one or more cerium species selected from the group consisting of cerium salts and cerium metal. Specific cerium species include cerium metal, cerium nitrate, cerium chloride, cerium acetate, cerium sulfate, and cerium hydroxide. In particular, cerium nitrate is preferably used because it is easy to handle and is a trivalent substance. As described above, in the manufactured fuel cell 101, sulfur that is about to adhere or has adhered to the electrodes is oxidized and decomposed in a potential cycle of normal operation, i.e., a potential cycle of -0.2 V or more and +0.5 V or less, and sulfur poisoning of the electrodes is suppressed. This sulfur poisoning suppression is performed without supplying any particular oxygen gas to the hydrogen electrode side, so there is little deterioration of the proton exchange membrane. Therefore, the manufactured fuel cell 101 is a high-output, high-efficiency fuel cell with little deterioration over time. EXAMPLES

[0036] Example 1 In Example 1, the modification of a platinum single crystal (111) electrode with cerium species was investigated by immersing the platinum single crystal (111) electrode in an aqueous solution of 0.01 M cerium nitrate and 0.1 M perchloric acid and bubbling the electrode with a mixed gas of argon and hydrogen. However, it should be noted that the present invention is not limited to such a specific form, and the technical scope of the present invention is defined by the claims.

[0037] <Sample preparation> A platinum single crystal (111) electrode (manufactured by Surface Preparation Laboratory) was prepared, brought into contact with a 0.01M cerium nitrate + 0.1M perchloric acid aqueous solution, and held for 1 hour while bubbling a mixed gas of argon and hydrogen. It was then washed with pure water and air-dried to obtain a platinum electrode. Here, the platinum single crystal (111) electrode has a purity of 99.99% or more, is cylindrical with a diameter of 10 mm, and is 5 mm thick.

[0038] <Sample evaluation> Electrochemical measurements of this electrode showed that the hydrogen adsorption / desorption waves specific to clean platinum surfaces, which appeared between -0.2 and +0.15 V, were reduced. This result supports the idea that cerium species (Ce species) were adsorbed on the surface (Figure 6). Here, for this electrochemical evaluation, a three-electrode beaker cell 102 shown in Fig. 5 was used. The three-electrode beaker cell 102 comprises an electrolyte 31, a container 32, a positive electrode (working electrode) 33, a negative electrode (counter electrode) 34, a reference electrode 35, a variable voltage power supply 36, an ammeter 37, and a voltmeter 38. In addition, when the platinum electrode was simply placed in contact with an aqueous solution containing cerium ions without bubbling with a mixed argon-hydrogen gas, the current-potential response was almost the same as that of an unmodified, clean platinum surface. This shows that bubbling a gas containing hydrogen is effective in adsorbing cerium species.

[0039] For reference, the same platinum single crystal (111) electrode as in Example 1 was used, but the current-potential response of the electrode was investigated for a sample in which electrochemical and XPS (X-ray Photoelectron Spectroscopy) measurements confirmed that sulfur had adhered to the electrode during normal use. The results are shown in Figure 7(b) alongside Figure 7(a), which shows the results for a bare platinum single crystal (111) electrode. It can be seen that the electrochemical activity is greatly suppressed by the adhesion of sulfur.

[0040] Example 2 In Example 2, the same platinum single crystal (111) electrode (manufactured by Surface Preparation Laboratory) as in Example 1 was prepared, and the platinum electrode (Ce-unmodified platinum electrode) was immersed in a 0.01 M cerium nitrate + 0.1 M perchloric acid aqueous solution as in Example 1, and the electrode potential was held at -0.2 V without bubbling with argon-hydrogen mixed gas. The reason for holding at -0.2 V is that when the platinum electrode is brought into contact with a 0.01 M cerium nitrate + 0.1 M perchloric acid aqueous solution while bubbling with argon-hydrogen mixed gas, the open circuit potential is approximately -0.2 V, which corresponds to the hydrogen electrode of the fuel electrode during operation. As a result, the addition and adsorption of cerium species became evident from the decrease in the hydrogen adsorption / desorption wave from the current-potential response, similar to the case of bubbling in Figure 4. In other words, it was demonstrated that in order to modify the platinum surface with cerium species, it is effective to maintain the potential at which the hydrogen electrode reaction occurs, in other words, near the potential of the hydrogen electrode of an operating fuel cell.

[0041] Example 3 In Example 3, it was confirmed by XPS (X-ray Photoelectron Spectroscopy) measurement that sulfur poisoning was suppressed by applying +0.2 V while maintaining the sample in an aqueous solution of 0.01 M cerium nitrate and 0.1 M perchloric acid. XPS measurements were carried out in the following states: sulfur was adsorbed on a platinum electrode modified with cerium species; and this electrode was held in an aqueous solution of 0.01M cerium nitrate + 0.1M perchloric acid and the potential was scanned from the oxidation peak at +0.2V to around +0.5V on the positive potential side. KRATOS NOVA (manufactured by SHIMADZU CORPORATION) was used as the XPS device. Figure 8 shows the measurement results before and after applying a voltage of 0.2V, using the HS - 2p 3 / 2 , H.S. - 2p 1 / 2 , S.O. 2 2- 2p 3 / 2 , S.O. 2 2p 3 / 2 The calculated values ​​and fitting curves created by combining these components are also shown.

[0042] In the sample in which sulfur was adsorbed on a platinum electrode modified with cerium species, a peak attributed to sulfur or sulfide ions appeared. Next, when the electrode was placed in an aqueous electrolyte solution and passed through an oxidation peak at +0.2 V, and then removed at +0.5 V, peaks due to sulfur oxides such as sulfur dioxide or sulfate ions appeared along with the sulfide ion peak. This indicates that the oxidation current appearing at +0.2 V is due to the oxidation of sulfur.

[0043] Example 4 In order to identify the surface adsorbed species, XAFS measurement was performed on a sample prepared in the same manner as in Example 1. Here, the XAFS measurement was carried out at the High Energy Accelerator Research Organization Photon Factory. The measurement results are shown in Fig. 9(a). Fig. 9(b) shows Ce(NO 3 ) 3 An example of a tetravalent cerium species is CeO 2 The results of the measurements are also shown in Fig. 9(c). For reference, the current-potential response of this sample is shown in Fig. 9(c). As is clear from a comparison of the two figures, a peak characteristic of trivalent cerium species appears at around 5726 eV in the sample of Example 1. This indicates that the cerium species adsorbed on the platinum electrode are trivalent ions (Ce 3+ ) was identified.

[0044] Example 5 In Example 5, the dependence on the number of potential cycles was examined. When sulfur is adsorbed onto a platinum surface that is not modified with cerium species, an oxidation current flows from about +0.7 to +1.0 V, as shown in Figure 10. This oxidation current gradually decreases with each potential cycle, while the current response from about -0.2 to +0.05 V, which is derived from the adsorption and desorption of hydrogen, increases. In other words, it was revealed that this oxidation current is derived from the oxidative decomposition of sulfur species, and that the platinum surface is gradually exposed by the repetition of potential cycles. On the other hand, when sulfur was adsorbed onto a platinum electrode modified with cerium species, an oxidation current appeared near +0.2 V in the current-potential curve, as shown in FIG.

[0045] From the above, it was revealed that at a platinum electrode modified with cerium species, repeated potential cycling in the region of -0.2 V to +0.5 V, which is more negative than that of unmodified, clean platinum, causes the oxidative desorption of adsorbed sulfur species. [Industrial Applicability]

[0046] According to the present invention, a platinum-based electrode, a fuel cell, and a method for manufacturing the same are provided, which prevent and suppress deterioration and changes over time due to sulfur poisoning without the need for additional equipment such as a filter that directly increases costs. Fuel cells are expected to be the next-generation energy source for mobility, and this technology is expected to have a significant impact on society and industry. This technology will also contribute to the widespread use of fuel cells, as it will no longer be necessary to excessively increase the purity of hydrogen fuel. [Explanation of symbols]

[0047] 11 Hydrogen electrode, platinum electrode 12 Hydrogen collector electrode 13 Oxygen electrode, platinum electrode 14 Oxygen collector electrode 15 Electrolytes 16 Wiring 17 Load, motor 31 Electrolytes 32 Container 33 Positive electrode (working electrode) 34 Negative electrode (counter electrode) 35 Reference pole 36 Variable voltage power supply 37 Ammeter 38 Voltmeter 51 Carbon 52 Platinum fine particles, Pt 53 Hydrogen, H 54 Hydrogen ion, H + 55 Hydrogen sulfide, H 2 S 56 Sulfur, S 57 Hydrogen gas, H 2 58 Cerium, Ce 59 Sulfur dioxide, SO 2 61 Carbon 62 Platinum, Pt 101 Fuel Cell 102 Three-electrode beaker cell

Claims

1. Platinum is at least a part of the material of the electrode; An electrode, wherein at least a portion of the platinum surface is modified with a substance that promotes the oxidative decomposition of sulfur.

2. 2. The electrode according to claim 1, wherein the substance that promotes the oxidative decomposition of sulfur is a cerium species selected from the group consisting of cerium salts and cerium metal.

3. 3. The electrode according to claim 2, wherein a ratio of an area of ​​the platinum modified by the cerium species to a surface area of ​​the platinum is 1% or more and 50% or less.

4. 4. The electrode according to claim 2, wherein the thickness of the cerium species modifying the platinum surface is from 0.1 atomic layer to 10 atomic layers.

5. 3. The electrode of claim 2, wherein said cerium salt is cerium nitrate.

6. 3. The electrode of claim 2, wherein the cerium valency in said cerium species is 3.

7. The electrode of claim 1 , wherein the platinum is in particulate form.

8. The electrode according to claim 7 , wherein the diameter of the microparticles, calculated by a spherical volume conversion method, is 1 nm or more and 10 nm or less.

9. Preparing an electrode member having platinum as at least a part of its constituent material; immersing the electrode member in a solution containing one or more cerium species selected from the group consisting of cerium salts and cerium metal; and bubbling with hydrogen gas or holding at −0.2 V; and drying the electrode.

10. The method for producing an electrode according to claim 9, wherein the solution is an aqueous solution containing cerium nitrate and perchloric acid.

11. The method for producing an electrode according to claim 10, wherein the concentration of the cerium nitrate is from 0.001 mol to 1 mol per 1 L of water which is a solvent for the aqueous solution.

12. A fuel cell having at least a hydrogen electrode, an oxygen electrode, and an electrolyte, A fuel cell, wherein the hydrogen electrode comprises platinum as at least a part of its constituent material, and at least a part of the surface of the platinum is modified with a substance that promotes the oxidative decomposition of sulfur.

13. 13. The fuel cell according to claim 12, wherein the substance that promotes the oxidative decomposition of sulfur is a cerium species selected from the group consisting of cerium salts and cerium metal.

14. 13. The fuel cell of claim 12, wherein the cerium salt is cerium nitrate.

15. 14. The fuel cell of claim 13, wherein the cerium valency in said cerium species is 3.

16. 16. The fuel cell of claim 12, wherein the platinum is in particulate form.

17. Providing an oxygen electrode, an electrolyte, and a hydrogen electrode having platinum as at least a portion of its components; The hydrogen electrode and the oxygen electrode are disposed so as to face each other via the electrolyte, A method for producing a fuel cell, wherein the hydrogen electrode is produced by the electrode production method according to any one of claims 9 to 11.

18. Providing an oxygen electrode, an electrolyte, and a hydrogen electrode having platinum as at least a portion of its components; disposing the hydrogen electrode and the oxygen electrode so as to face each other via the electrolyte; A method for producing the fuel cell according to any one of claims 12 to 15, comprising adding a substance that promotes oxidative decomposition of sulfur to the electrolyte.

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