Fuel cell, method for operating fuel cell, and fuel cell system

Abstract

A fuel cell comprising: a cathode catalyst layer containing a cathode-side proton-conductive ionomer; an anode catalyst layer; and an electrolyte layer disposed between the cathode catalyst layer and the anode catalyst layer and containing a proton conductor, wherein the cathode-side proton-conductive ionomer contains a Group 16 element-oxygen-acid compound, and the proton conductor contains a Group 15 element-oxygen-acid compound.

Description

Fuel cell, fuel cell operation method, and fuel cell system

[0001] The present invention relates to a fuel cell, a method for operating a fuel cell, and a fuel cell system.

[0002] Fuel cells have been studied for a long time for the purpose of reducing the environmental load, etc., due to their excellent energy conversion efficiency.

[0003] Known fuel cells include polymer electrolyte fuel cells that operate at low temperatures below 100° C. and solid oxide fuel cells that operate at high temperatures above 600° C.

[0004] Compared to fuel cells with operating temperatures below 100° C., fuel cells with high operating temperatures of 100° C. or higher can be used with a variety of fuels and can further increase the overall energy conversion efficiency by using waste heat as a heating source, etc. For this reason, fuel cells that operate in the medium temperature range, between 100° C. and 300° C., are desired, and have been studied for some time (see, for example, Patent Document 1).

[0005] Japanese Patent Application Publication No. 2012-49116

[0006] However, many of the fuel cells that have been studied to date that operate in the medium temperature range contain phosphoric acid in the electrolyte. In such cases, when manufacturing the fuel cell, platinum and other catalysts used on the cathode side can be poisoned by phosphoric acid, resulting in insufficient output characteristics.

[0007] Therefore, an object of the present invention is to provide a fuel cell with excellent output characteristics.

[0008] The fuel cell of the present invention comprises: a cathode catalyst layer containing a cathode-side proton-conductive ionomer; an anode catalyst layer; and an electrolyte layer containing a proton conductor, the electrolyte layer being disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton-conductive ionomer contains a Group 16 element oxyacid compound, and the proton conductor contains a Group 15 element oxyacid compound.

[0009] The present invention can provide a fuel cell with excellent output characteristics.

[0010] FIG. 1 is an explanatory diagram of a configuration example of a fuel cell according to one embodiment of the present disclosure. FIG. 2 is an explanatory diagram of another configuration example of a fuel cell according to one embodiment of the present disclosure. FIG. 3A is an explanatory diagram of an example of a proton conductor in an electrolyte layer. FIG. 3B is an explanatory diagram of an example of a proton conductor in an electrolyte layer. FIG. 3C is an explanatory diagram of an example of a proton conductor in an electrolyte layer. FIG. 3D is an explanatory diagram of an example of a proton conductor in an electrolyte layer. FIG. 3E is an explanatory diagram of an example of a proton conductor in an electrolyte layer. FIG. 4 is an explanatory diagram of an example of a fuel cell system according to one embodiment of the present disclosure. FIG. 5 shows evaluation results of VI characteristics in Example 1 and Comparative Example 1.

[0011] DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described below with reference to the accompanying drawings, in which:

[0024] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings.

[0025] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings.

[0026] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings.

[0027] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings.

[0028] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings.

[0029] A fuel cell according to one embodiment of the present disclosure (hereinafter referred to as "embodiment") will be described with reference to the accompanying drawings. [0

[0012] It should be noted that the drawings are all schematic diagrams for explaining the configuration of the fuel cell and other components of the present embodiment, and do not accurately depict the dimensions and other details.

[0013] As shown in FIG. 1, the fuel cell 10 of this embodiment has a cathode catalyst layer 11, an anode catalyst layer 12, and an electrolyte layer 13 disposed between the cathode catalyst layer 11 and the anode catalyst layer 12.

[0014] Each component will be described below: (1) Cathode Catalyst Layer The components contained in the cathode catalyst layer will be described below: (1-1) Cathode-Side Proton-Conductive Ionomer The cathode catalyst layer can contain a cathode-side proton-conductive ionomer.

[0015] An ionomer is a material that provides ionic conductivity in the cathode catalyst layer and anode catalyst layer, which are electrodes; in other words, a material that imparts ionic conductivity to the cathode catalyst layer and anode catalyst layer. A proton-conducting ionomer is a material that conducts protons. Adding an ionomer allows the catalytic components, such as platinum, to function effectively in the thickness direction of the electrode, greatly improving the performance of the fuel cell.

[0016] The cathode-side proton-conductive ionomer may contain a Group 16 element oxygen acid compound. The cathode-side proton-conductive ionomer may be composed solely of a Group 16 element oxygen acid compound, but this does not exclude the possibility of unavoidable impurities being mixed in.

[0017] The inventors of the present invention have conducted research into fuel cells that operate in the medium temperature range (100°C or higher and 300°C or higher). For fuel cells that operate in the medium temperature range, the use of phosphoric acid-based materials as proton-conductive ionomers in the cathode catalyst layer has been considered. However, the cathode catalyst layer uses metals such as platinum as a cathode catalyst to promote the cathode reaction. When a phosphoric acid-based material is used as a proton-conductive ionomer, the catalyst is poisoned immediately after production, and the output characteristics cannot be sufficiently improved.

[0018] In contrast, in the fuel cell of this embodiment, the cathode catalyst layer 11 contains a Group 16 element oxyacid compound as the cathode-side proton-conducting ionomer. Compared to when a phosphoric acid-based material is used, the Group 16 element oxyacid compound can reduce the poisoning of metals such as platinum used in the cathode catalyst layer. Group 16 element oxyacid compounds have the property of being reductively decomposed when used in a reducing atmosphere, but in a fuel cell, the cathode catalyst layer is an oxygen electrode and is in an oxidizing atmosphere, so there is no risk of reductive decomposition.

[0019] Therefore, by containing a Group 16 element oxygen acid compound as the cathode-side proton-conductive ionomer in the cathode catalyst layer 11, it is possible to reduce the poisoning of the cathode catalyst layer 11 as described above and improve the output characteristics of the fuel cell 10.

[0020] The Group 16 element oxyacid compound is an oxyacid compound containing an element of Group 16 of the periodic table.

[0021] Examples of Group 16 elements include sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). However, it is particularly preferable to use an oxygen acid compound of one or more elements selected from sulfur (S) and selenium (Se) as the Group 16 element oxygen acid compound. Therefore, the Group 16 element oxygen acid compound may be a sulfur-selenium-based oxygen acid compound.

[0022] The oxygen acid compound means a compound containing an inorganic acid containing oxygen, and for example, a hydrogen acid salt can be used.

[0023] The Group 16 element oxyacid compound is not particularly limited, but for example, as described above, one or more types selected from sulfuric acid-based oxyacid compounds and selenium-based oxyacid compounds can be used.

[0024] Among the group 16 element oxygen acid compounds, examples of sulfuric acid-based oxygen acid compounds include sulfuric acid-based hydrogen salts. Examples of sulfuric acid-based hydrogen salts include RbHSO ４ , K.H.S.O. ４ , K. ３ H (SO ４ ) ２ , CsHSO ４ , N.H. ４ HSO ４ etc.

[0025] Among the group 16 element oxygen acid compounds, examples of selenium-based oxygen acid compounds include selenium-based hydrochlorides. ３ H(SeO ４ ) ２ , Rb ３ H(SeO ４ ) ２ , K. ３ H(SeO ４ ) ２ , N.H. ４ HSeO ４ etc.

[0026] The Group 16 element oxyacid compound contained in the cathode-side proton-conducting ionomer preferably contains a sulfate-based hydrogen salt. This is because sulfur is easier to handle than other Group 16 elements, and sulfur-containing sulfate-based hydrogen salts also have excellent proton conductivity in the medium temperature range. The Group 6 element oxyacid compound may be composed solely of a sulfate-based hydrogen salt, but even in this case, this does not exclude the possibility of unavoidable impurities being mixed into the Group 6 element oxyacid compound.

[0027] In particular, the Group 16 element oxygen acid compound contained in the cathode-side proton-conducting ionomer is cesium hydrogen sulfate (CsHSO ４ ) is preferably contained. This is because cesium hydrogen sulfate is a stable substance with particularly excellent proton conductivity in the medium temperature range. The Group 16 element oxyacid compound may be composed solely of cesium hydrogen sulfate, but even in this case, this does not exclude the possibility of unavoidable impurities being mixed into the Group 16 element oxyacid compound.

[0028] It is preferable that the content of phosphoric acid compounds in the cathode-side proton-conductive ionomer of the cathode catalyst layer 11 is suppressed. For example, the content of phosphoric acid compounds can be 5% by mass or less, or 1% by mass or less, or even 0.1% by mass or less. The cathode-side proton-conductive ionomer may contain no phosphoric acid compounds, i.e., the content may be 0, but this does not exclude the inclusion of phosphoric acid compounds as unavoidable impurities. Examples of phosphoric acid compounds include various phosphates.

[0029] The Group 16 element oxyacid compound used as the cathode-side proton-conducting ionomer is preferably solid at least at room temperature (27°C). Therefore, the Group 16 element oxyacid compound, sulfate-based hydrogen salt, selenium-based hydrogen salt, etc. may be expressed as Group 16 element solid oxyacid compound, sulfate-based solid hydrogen salt, selenium-based solid hydrogen salt, etc., respectively. (1-2) Cathode Catalyst The cathode catalyst layer 11 can contain a cathode catalyst that promotes the cathode reaction.

[0030] The cathode reaction is represented by the following formula, for example: ＋ +0.5O２ +2e － → H ２ O

[0031] The cathode catalyst is not particularly limited, and may be one or more selected from metals and alloys supported on a carrier such as carbon, conductive oxide, etc. Alternatively, one or more selected from metals and alloys may be directly supported on the cathode-side proton-conductive ionomer.

[0032] Examples of the metal include platinum, gold, silver, etc. Examples of the alloy include an alloy containing one or more metals selected from platinum, gold, silver, etc.

[0033] The carrier such as carbon exemplified as the cathode catalyst functions as an electron conductor, and can provide a current collecting function to the cathode catalyst layer 11. (1-3) Other Components The cathode catalyst layer 11 can also contain any other components such as a binder in addition to the cathode-side proton-conductive ionomer and the cathode catalyst.

[0034] The cathode catalyst layer 11 may be manufactured, for example, by pressing a mixture of a cathode-side proton-conductive ionomer and a cathode catalyst. Alternatively, the cathode catalyst layer 11 may be manufactured, for example, by applying a mixture of a cathode-side proton-conductive ionomer, a cathode catalyst, and a binder to the first surface 131 of the electrolyte layer 13. (2) Electrolyte Layer As shown in FIG. 1 , the electrolyte layer 13 can be disposed between the cathode catalyst layer 11 and the anode catalyst layer 12 and can contain a proton conductor.

[0035] For example, as shown in FIG. 1 , the electrolyte layer 13 may be disposed so as to be in contact with the cathode catalyst layer 11 and the anode catalyst layer 12. Here, the surface of the electrolyte layer 13 facing the cathode catalyst layer 11 is defined as a first surface 131, and the surface of the electrolyte layer 13 facing the anode catalyst layer 12 is defined as a second surface 132. The first surface 131 and the second surface 132 are surfaces located on opposite sides of the electrolyte layer 13. In this case, for example, the first surface 131 of the electrolyte layer 13 may be disposed so as to be in contact with the cathode catalyst layer 11, and the second surface 132 of the electrolyte layer 13 may be disposed so as to be in contact with the anode catalyst layer 12. (2-1) Proton Conductor (Regarding the Proton Conductor Material) The electrolyte layer 13 may contain an ion conductor, which is an electrolyte. The electrolyte layer 13 may contain, as an ion conductor, protons (H ＋ ) can be included as a proton conductor.

[0036] The proton conductor of the electrolyte layer 13 may contain a Group 15 element oxygen acid compound. Group 15 element oxygen acid compounds exhibit high proton conductivity in the medium temperature range, particularly at temperatures above 200°C, and particularly above 200°C. Therefore, by including a Group 15 element oxygen acid compound as a proton conductor in the electrolyte layer 13 of the fuel cell 10, the fuel cell 10 can be made to operate in the medium temperature range. Furthermore, since Group 15 element oxygen acid compounds are stable even in a reducing atmosphere, when used in the electrolyte layer 13, reductive decomposition of the Group 15 element oxygen acid compound serving as a proton conductor hardly occurs, thereby stabilizing the output characteristics of the fuel cell 10. The proton conductor of the electrolyte layer 13 may be composed solely of a Group 15 element oxygen acid compound, but even in this case, this does not exclude the possibility of unavoidable impurities being mixed into the proton conductor of the electrolyte layer 13.

[0037] The Group 15 element oxyacid compound is an oxyacid compound containing an element of Group 15 of the periodic table.

[0038] Examples of Group 15 elements include phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). However, it is particularly preferable to use an oxygen acid compound of one or more elements selected from phosphorus (P) and arsenic (As) as the Group 15 element oxygen acid compound. Therefore, the Group 15 element oxygen acid compound may be a phosphorus-arsenic-based oxygen acid compound.

[0039] The oxygen acid compound means a compound containing an inorganic acid containing oxygen, and for example, a hydrogen acid salt can be used.

[0040] The Group 15 element oxyacid compound is not particularly limited, but for example, as described above, one or more types selected from phosphorus-based oxyacid compounds and arsenic-based oxyacid compounds can be used.

[0041] Among the group 15 element oxygen acid compounds, examples of phosphorus-based oxygen acid compounds include hydrophosphates. Examples of hydrophosphates include RbH ２ P.O. ４ , CsH ２ P.O. ４ , K.H. ２ P.O. ４ , LiH ２ P.O. ４ etc.

[0042] Among the group 15 element oxygen acid compounds, arsenic-based oxygen acid compounds include arsenic hydrochlorides. ２ AsO ４ , K.H. ２ AsO ４ , N.H. ４ H ２ AsO ４ etc.

[0043] The Group 15 element oxyacid compound contained in the proton conductor of the electrolyte layer 13 preferably contains a phosphate-based hydrophosphate. This is because phosphorus is easier to handle than other Group 15 elements, and phosphorus-containing phosphate-based hydrophosphates also have excellent proton conductivity in the medium temperature range. The Group 15 element oxyacid compound may be composed solely of a phosphate-based hydrophosphate, but even in this case, this does not exclude the possibility of unavoidable impurities being mixed into the Group 15 element oxyacid compound.

[0044] In particular, the Group 15 element oxygen acid compound contained in the proton conductor of the electrolyte layer 13 is cesium dihydrogen phosphate (CsH ２ P.O. ４) is preferably contained. This is because cesium dihydrogen phosphate is a stable substance with particularly excellent proton conductivity in the medium temperature range. The Group 15 element oxyacid compound may be composed solely of cesium dihydrogen phosphate, but even in this case, this does not exclude the possibility of unavoidable impurities being mixed into the Group 15 element oxyacid compound.

[0045] The Group 15 element oxyacid compound used as the proton conductor is preferably solid at least at room temperature (27° C.), and therefore the Group 15 element oxyacid compound, phosphate-based hydrochloride, arsenic-based hydrochloride, etc. may be written as Group 15 element solid oxyacid compound, phosphate-based solid hydrochloride, arsenic-based solid hydrochloride, etc., respectively.

[0046] The Group 15 element oxyacid compound serving as a proton conductor may be contained in a portion of the electrolyte layer 13, or may be contained in the entire electrolyte layer 13. In other words, the electrolyte layer 13 may contain only the Group 15 element oxyacid compound as a proton conductor, or may contain other components.

[0047] For example, examples of changes in the mass ratio of the Group 15 element oxygen acid compound in the proton conductor along the thickness direction of the electrolyte layer 13 are shown in FIGS. 3A to 3E.

[0048] 3A to 3E, the horizontal axis indicates the position along the thickness direction of the electrolyte layer 13. The first surface and the second surface refer to the end surfaces of the electrolyte layer 13, and the region sandwiched between the first surface and the second surface constitutes the electrolyte layer 13. The definitions of the first surface and the second surface have already been explained.

[0049] 3A to 3E, the vertical axis represents the mass ratio of the Group 15 element oxygen acid compound in the proton conductor. Note that Figs. 3A to 3E are merely examples, and the present invention is not limited to these examples.

[0050] For example, as shown in FIG. 3A, the entire electrolyte layer 13 may contain a Group 15 element oxygen acid compound as a proton conductor.

[0051] 3B , a first layer 31 including the first surface of the electrolyte layer 13 and a second layer 32 including the second surface thereof may contain a Group 15 element oxygen acid compound as a proton conductor. The material contained as a proton conductor in a third layer 33 between the first layer 31 and the second layer 32 is not particularly limited, and may be, for example, a Group 16 element oxygen acid compound. While FIG. 3B shows an example in which the electrolyte contains three proton conductor layers, the electrolyte is not limited to this form and may contain four or more proton conductor layers with different configurations.

[0052] When the electrolyte layer 13 contains a Group 16 element oxygen acid compound, the Group 16 element oxygen acid compound contained in the cathode-side proton-conductive ionomer may be the same as or different from the Group 16 element oxygen acid compound contained in the electrolyte layer 13. The Group 16 element oxygen acid compound that can be suitably used in the electrolyte layer 13 is the same as the Group 16 element oxygen acid compound described in the cathode-side proton-conductive ionomer, and therefore a description thereof will be omitted.

[0053] In addition, in the portions where the Group 15 element oxyacid compound is disposed in FIGS. 3A and 3B, the proton conductor is composed solely of the Group 15 element oxyacid compound, but this is not a limitation.

[0054] For example, a mixture of a Group 15 element oxygen acid compound and another proton conductor, such as a Group 16 element oxygen acid compound, may be used. In this case, the mass proportion of the Group 15 element oxygen acid compound in the proton conductor will be less than 100%, as shown by the solid line 34 in FIG. 3C . While FIG. 3C shows an example in which the mass proportion of the Group 15 element oxygen acid compound in the proton conductor is constant, the mass proportion of the Group 15 element oxygen acid compound in the proton conductor may vary depending on the position within the electrolyte layer 13, as shown by the two-dot chain line 35. In the example shown by the two-dot chain line 35, the mass proportion of the Group 15 element oxygen acid compound varies monotonically, but this is not a limitation.

[0055] When the electrolyte layer 13 contains a Group 16 element oxygen acid compound in addition to the Group 15 element oxygen acid compound as a proton conductor, in order to avoid reductive decomposition of the Group 16 element oxygen acid compound, it is preferable that the content of the Group 16 element oxygen acid compound is small at least on the second surface of the electrolyte layer 13. In particular, on the second surface of the electrolyte layer 13, the proportion of the Group 16 element oxygen acid compound in the total of the Group 15 element oxygen acid compound and the Group 16 element oxygen acid compound is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less.

[0056] On the second surface of the electrolyte layer 13, the mass proportion of the Group 16 element oxygen acid compound may be 0. In this case, the proportion of the Group 15 element oxygen acid compound of the total of the Group 15 element oxygen acid compound and the Group 16 element oxygen acid compound on the second surface of the electrolyte layer 13 can be 100 mass%.

[0057] In the example shown in FIGS. 3A to 3C, the first surface 131 and the second surface 132 of the electrolyte layer 13 contain a Group 15 element oxygen acid compound as a proton conductor.

[0058] As already described, there are no particular limitations on the composition between the first surface 131 and the second surface 132. The proton conductor between the first surface 131 and the second surface 132 may also contain a Group 15 element oxyacid compound, or may contain a proton conductor other than a Group 15 element oxyacid compound.

[0059] The mass ratio of the Group 15 element oxygen acid compound on the first surface 131 and the second surface 132 may be the same or different.

[0060] When a Group 15 element oxygen acid compound is contained as a proton conductor between the first surface 131 and the second surface 132, the concentration of the Group 15 element oxygen acid compound may be constant, or, for example, the concentration may increase or decrease from the first surface 131 to the second surface 132.

[0061] 3D , the first layer 36 including the first surface may not contain a Group 15 element oxyacid compound as a proton conductor, but may contain a Group 16 element oxyacid compound other than a Group 15 element oxyacid compound, for example, an oxyacid compound of a Group 16 element. The second layer 37 including the second surface may contain a Group 15 element oxyacid compound as a proton conductor.

[0062] Although Fig. 3D shows a case in which the mass proportion of the Group 15 element oxygen acid compound in the proton conductor changes suddenly between the first layer 36 and the second layer 37, this is not a limitation. For example, as shown in Fig. 3E , a transition layer 38 may be provided between the first layer 36 and the second layer 37 so that the mass proportion of the Group 15 element oxygen acid compound in the proton conductor changes gradually. In Fig. 3E , the mass proportion of the Group 15 element oxygen acid compound in the proton conductor in the transition layer 38 changes linearly, but this is not a limitation and can be selected arbitrarily. Furthermore, the number of proton conductor layers in the electrolyte layer 13 is not limited to the configurations shown in Figs. 3D and 3E .

[0063] As described with reference to Figures 3D and 3E, the first surface 131 of the electrolyte layer 13 may contain a Group 16 element oxygen acid compound as a proton conductor, and the second surface 132 of the electrolyte layer 13 may contain a Group 15 element oxygen acid compound as a proton conductor.

[0064] As explained above regarding the cathode catalyst layer, using a phosphoric acid-based material in the cathode catalyst layer may poison the cathode catalyst contained in the cathode catalyst layer 11. If the Group 15 element oxygen acid compound contained in the electrolyte layer 13 is a phosphoric acid-based compound, it does not come into contact with the cathode catalyst contained in the cathode catalyst layer 11, but may gradually become poisoned due to material diffusion during operation. By including a Group 16 element oxygen acid compound as a proton conductor in the first surface 131, the performance degradation due to the diffusion can be reduced. This particularly reduces the poisoning of the cathode catalyst contained in the cathode catalyst layer 11, thereby particularly improving the long-term output characteristics of the fuel cell 10. (Regarding Composite Formation) The Group 15 element oxygen acid compound contained in the electrolyte layer 13 may be composited (composite-formed).

[0065] The form of the composite is not particularly limited, and the proton conductor may be mixed with a composite material other than the proton conductor and dispersed in the composite material, or the proton conductor may be supported on the surface of particles or membranes of the composite material or inside the voids of the particles.

[0066] By forming a composite of the Group 15 element oxyacid compound, the physical properties and handling properties can be improved, and the properties of the electrolyte layer 13 can be enhanced.

[0067] For example, the Group 15 element oxyacid compound contained in the electrolyte layer 13 may be composited with an inorganic oxide. Inorganic oxides are generally stable, and therefore, by composited with the Group 15 element oxyacid compound, the properties of the electrolyte layer 13 can be improved while preventing adverse effects on the properties of the Group 15 element oxyacid compound, such as the proton conductivity properties.

[0068] Examples of inorganic oxides include silicon oxide (SiO ２ ), titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ) and the like can be used. When the electrolyte layer 13 contains a material other than a Group 15 element oxygen acid compound as a proton conductor, these materials may also be composited. That is, at least a portion of the proton conductor may be composited, or the proton conductor may be composited. (2-2) Regarding Other Components The electrolyte layer 13 may further contain any component other than the proton conductor. The electrolyte layer 13 may also contain a component for stabilizing the shape of the electrolyte layer 13, such as a binder.

[0069] It is preferable that the electrolyte layer 13 does not contain a fluorine-based proton conductor, for example, an organic compound containing fluorine. This is because fluorine-based proton conductors have low heat resistance, which may make it difficult to operate the fuel cell 10 at temperatures of, for example, 200°C or higher. (3) Anode Catalyst Layer The components contained in the anode catalyst layer are described below. (3-1) Anode-Side Proton-Conductive Ionomer The anode catalyst layer can contain an anode-side proton-conductive ionomer.

[0070] The anode-side proton-conductive ionomer may contain a Group 15 element oxygen acid compound. The anode-side proton-conductive ionomer may be composed solely of a Group 15 element oxygen acid compound, but this does not exclude the possibility of unavoidable impurities being mixed in.

[0071] The anode catalyst layer, which is the fuel electrode, is prone to a reducing atmosphere. However, since the Group 15 element oxygen acid compound is stable even in a reducing atmosphere, the use of the Group 15 element oxygen acid compound as the anode-side proton-conductive ionomer can stably improve the output characteristics of the fuel cell 10.

[0072] The Group 15 element oxygen acid compound is not particularly limited, and can be, for example, the Group 15 element oxygen acid compound described in the proton conductor of the electrolyte layer 13. The Group 15 element oxygen acid compound contained in the electrolyte layer 13 and the Group 15 element oxygen acid compound contained in the anode-side proton-conductive ionomer can be the same or different. As the Group 15 element oxygen acid compound, for example, one or more types selected from phosphorus-based oxygen acid compounds and arsenic-based oxygen acid compounds can be used.

[0073] Among the group 15 element oxygen acid compounds, examples of phosphorus-based oxygen acid compounds include hydrophosphates. Examples of hydrophosphates include RbH ２ P.O. ４ , CsH ２ P.O. ４ , K.H. ２ P.O. ４ , LiH ２ P.O. ４ etc.

[0074] Among the group 15 element oxygen acid compounds, arsenic-based oxygen acid compounds include arsenic hydrochlorides. ２ AsO ４ , K.H. ２ AsO ４ , N.H. ４ H ２ AsO ４ etc.

[0075] The Group 15 element oxygen acid compound preferably contains a phosphate-based hydrophosphate. This is because phosphorus is easier to handle than other Group 15 elements, and phosphorus-containing phosphate-based hydrophosphates also have excellent proton conductivity in the medium temperature range. The Group 15 element oxygen acid compound may be composed solely of a phosphate-based hydrophosphate, but even in this case, this does not exclude the possibility of the Group 15 element oxygen acid compound being contaminated with other Group 15 element oxygen acid compounds or unavoidable impurities.

[0076] The Group 15 element oxyacid compound preferably contains cesium dihydrogen phosphate. This is because cesium dihydrogen phosphate is a stable substance with particularly excellent proton conductivity in the medium temperature range. The Group 15 element oxyacid compound may be composed solely of cesium dihydrogen phosphate, but this does not exclude the possibility of unavoidable impurities being mixed in. (3-2) Anode Catalyst The anode catalyst layer 12 can contain an anode catalyst that promotes the anode reaction.

[0077] The anodic reaction can be expressed by the following formula, for example: ２ → 2H ＋ +2e －

[0078] The anode catalyst is not particularly limited, and may be one or more selected from metals and alloys supported on a support such as carbon, conductive oxide, etc. Alternatively, one or more selected from metals and alloys may be directly supported on the anode-side proton-conductive ionomer.

[0079] Examples of the metal include platinum, gold, silver, etc. Examples of the alloy include an alloy containing one or more metals selected from platinum, gold, silver, etc.

[0080] The anode catalyst layer 12 may contain any other components such as a binder in addition to the anode-side proton-conductive ionomer and the anode catalyst.

[0081] The anode catalyst layer 12 may be manufactured by, for example, pressing a mixture of an anode-side proton-conductive ionomer and an anode catalyst. Alternatively, the anode catalyst layer 12 may be manufactured by, for example, applying a mixture of an anode-side proton-conductive ionomer, an anode catalyst, and a binder to the second surface 132 of the electrolyte layer 13. (4) Other Components (Diffusion Layer, Separator) As shown in FIG. 2 , the fuel cell 20 of this embodiment may include, in addition to the cathode catalyst layer 11, the anode catalyst layer 12, and the electrolyte layer 13, a diffusion layer 21, a separator 22, and the like. The fuel cell 20 of this embodiment may include either the diffusion layer 21 or the separator 22, or both. The presence or absence of the diffusion layer 21 and the separator 22 and their configurations may be different or the same between the cathode catalyst layer 11 side and the anode catalyst layer 12 side. (Organic Hydride Supply Device) The fuel cell 20 of this embodiment can also supply hydrogen to the anode catalyst layer 12, which is the fuel electrode, to generate power. However, the fuel cell is not limited to this configuration, and can further include an organic hydride supply device 23 that supplies a hydrogen supply substance, i.e., an organic hydride that is a hydrogen carrier (hydrogen storage material), to the anode catalyst layer 12, as in the fuel cell 20 shown in FIG.

[0082] The organic hydride supply device 23 may be configured to supply an organic hydride to the anode catalyst layer 12. For this purpose, the organic hydride supply device 23 may include, for example, a tank for storing the organic hydride, a pump for transporting the organic hydride from the tank to the anode catalyst layer 12, and the like.

[0083] Furthermore, the organic hydride may be supplied alone or together with some kind of carrier gas (accompanying gas). When the organic hydride is supplied to the fuel cell 20 by a carrier gas, the fuel cell 20 of this embodiment may also have a carrier gas supply device 231 for supplying the carrier gas. The carrier gas supply device 231 may have a carrier gas tank for storing the carrier gas, and a flow meter, a valve, a mass flow controller, etc. for measuring, adjusting, and controlling the amount of carrier gas supplied.

[0084] In Figure 2, the carrier gas supply device 231 is connected to a pipe connecting the organic hydride supply device 23 and the fuel cell 20, but this is not limited to this form, and the carrier gas supply device 231 may be provided inside the organic hydride supply device 23, etc.

[0085] The organic hydride supplied to the anode catalyst layer 12 can release hydrogen by utilizing, for example, heat generated by the fuel cell 20, thereby supplying hydrogen to the anode catalyst layer 12. After releasing hydrogen, the organic hydride is recovered in the organic hydride recovery device 24 and re-hydrogenated, allowing it to be reused as a hydrogen carrier.

[0086] The configuration of the organic hydride recovery device 24 is not particularly limited, but may include, for example, a tank for storing the recovered organic hydride.

[0087] The organic hydride supplied by the organic hydride supply device 23 may be any organic compound capable of undergoing hydrogenation and dehydrogenation through a reversible reaction, and its type, etc., is not particularly limited. The organic hydride is not particularly limited, but may include one or more types selected from cyclohexane, decalin, methylcyclohexane, 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane, 1-methyldecalin, 2-methyldecalin, perhydrobenzyltoluene, perhydrodibenzyltoluene, etc.

[0088] The cathode catalyst layer 11 can be supplied with an oxygen-containing gas, such as an oxygen-containing gas. Examples of the oxygen-containing gas include oxygen gas and air. (Heating Device, Cooling Device) The fuel cell 20 can also include a heating device for heating the cathode catalyst layer 11, the anode catalyst layer 12, and the electrolyte layer 13 to a predetermined operating temperature (driving temperature) during startup, or a cooling device for cooling the fuel cell 20 and recovering heat generated by the fuel cell 20. The heating device may be a heater capable of heating some or all of the components of the fuel cell 20, or may heat the fuel cell 20 by heating raw materials such as the oxygen-containing gas supplied to the fuel cell 20. (Humidifying Device) The fuel cell of this embodiment is preferably operated while humidifying the gas supplied to the cathode catalyst layer 11 and the anode catalyst layer 12 and humidifying the electrolyte layer 13. This is because humidifying the electrolyte layer 13 suppresses the dehydration decomposition reaction of oxygen acid compounds and ensures stable performance over a long period of time.

[0089] The humidifier may be configured to humidify, for example, either or both of the gas supplied to the cathode catalyst layer 11 or the gas supplied to the anode catalyst layer 12. Therefore, the humidifier may include, for example, a device for bubbling the gas supplied to the fuel cell into water or a mixing device for mixing the gas supplied to the fuel cell with a gas containing water. [Method of Operating the Fuel Cell] A method of operating the fuel cell of this embodiment will now be described.

[0090] A fuel cell according to one aspect of the present disclosure can be used as a fuel cell for use in the fuel cell operating method of this embodiment.

[0091] Therefore, the method for operating a fuel cell according to this embodiment can operate a fuel cell including the following cathode catalyst layer 11, anode catalyst layer 12, and electrolyte layer 13.

[0092] The cathode catalyst layer 11 can contain a cathode-side proton-conducting ionomer.

[0093] The electrolyte layer 13 is disposed between the cathode catalyst layer 11 and the anode catalyst layer 12 and can contain a proton conductor.

[0094] The cathode-side proton-conductive ionomer may contain a Group 16 element oxyacid compound, and the proton conductor may contain a Group 15 element oxyacid compound.

[0095] The method for operating the fuel cell of this embodiment can include an operating step of operating the fuel cell. (1) Operating Step In the operating step, for example, an oxygen-containing gas can be supplied to the cathode catalyst layer 11, and hydrogen can be supplied to the anode catalyst layer 12. The method for supplying hydrogen to the anode catalyst layer 12 is not particularly limited, and hydrogen gas can be supplied to the anode catalyst layer 12, or a hydrogen storage material such as an organic hydride can be supplied to the anode catalyst layer 12, and hydrogen can be supplied from the hydrogen storage material by a dehydrogenation reaction.

[0096] The operating conditions of the fuel cell in the operation step are not particularly limited, but for example, the fuel cell may be operated at an operating temperature of 190° C. to 230° C. and a water vapor partial pressure of 0.3 atm or more, or at an operating temperature of 200° C. to 220° C. and a water vapor partial pressure of 0.35 atm to 0.45 atm. (2) Warm-up Step The fuel cell operation method of this embodiment may also have a warm-up step before the operation step.

[0097] In the warm-up step, the temperature of the fuel cell is set to 240° C. or higher and 260° C. or lower before the operating step, and then the temperature of the fuel cell can be changed to the operating conditions of the operating step, i.e., the operating temperature.

[0098] By performing the warm-up step and heating the Group 15 element oxyacid compound to 240°C or higher and 260°C or lower, it is possible to prevent decomposition of the Group 15 element oxyacid compound and induce proton conductivity through transition (crystal structure transition). Even when the temperature is subsequently lowered to the operating temperature, the proton conductivity of the Group 15 element oxyacid compound can be increased. [Fuel Cell System] A fuel cell system will now be described.

[0099] 4, a fuel cell system 40 may include a fuel cell 41. As the fuel cell 41, a fuel cell according to an aspect of the present disclosure may be used.

[0100] Therefore, the fuel cell 41 included in the fuel cell system 40 can contain the following cathode catalyst layer 11, anode catalyst layer 12, and electrolyte layer 13.

[0101] The cathode catalyst layer 11 can contain a cathode-side proton-conducting ionomer.

[0102] The electrolyte layer 13 is disposed between the cathode catalyst layer 11 and the anode catalyst layer 12 and can contain a proton conductor.

[0103] The cathode-side proton-conductive ionomer may contain a Group 16 element oxyacid compound, and the proton conductor may contain a Group 15 element oxyacid compound.

[0104] Materials suitable for use as the cathode-side proton-conducting ionomer and proton conductor have already been described, and therefore further description will be omitted. For example, the cathode-side proton-conducting ionomer may contain a sulfate-based hydrogen salt, and the proton conductor may contain a phosphate-based hydrogen salt.

[0105] The fuel cell system 40 of this embodiment is not particularly limited in its use, and can be used for various purposes such as home use and business use, and can also be used as a stationary fuel cell system. Therefore, in addition to the fuel cell 41, the fuel cell system 40 of this embodiment can also have a power receiving facility 42 that receives the power generated by the fuel cell 41.

[0106] The fuel cell included in the fuel cell system 40 of this embodiment can also be used as a stack by stacking cells each including a cathode catalyst layer 11, an anode catalyst layer 12, and an electrolyte layer 13.

[0107] Specific examples will be given below for explanation, but the present invention is not limited to these examples. Example 1 (1) Fabrication of a fuel cell A fuel cell was fabricated according to the following procedure.

[0108] A 1.9 mm diameter mold was prepared, and the materials for the anode catalyst layer, electrolyte layer, and cathode catalyst layer were placed in the mold in the order shown below and pressed to fabricate a fuel cell. (Anode Catalyst Layer) After placing a metal mesh to protect the end faces, 100 mg of a mixed powder for the anode catalyst layer, consisting of platinum-supported carbon and cesium dihydrogen phosphate, a Group 15 element oxyacid compound, mixed in a 1:2 mass ratio, was placed on top of the material for the anode catalyst layer. (Electrolyte Layer) 100 mg of cesium dihydrogen phosphate, a Group 15 element oxyacid compound, was placed on top of the material for the electrolyte layer. (Cathode Catalyst Layer) 50 mg of a mixed powder for the cathode catalyst layer, consisting of platinum-supported carbon and cesium hydrogen sulfate, a Group 16 element oxyacid compound, mixed in a 1:2 mass ratio, was placed on top of the material for the electrolyte layer. (2) Operation and evaluation of fuel cell The fabricated fuel cell was operated by supplying hydrogen and air to the anode catalyst layer and cathode catalyst layer under the following conditions, and the VI characteristics were measured using an electrochemical measurement device with a four-terminal method. A heater and thermocouple were incorporated into the fuel cell itself, and the temperature during operation was controlled by the heater output to maintain 230°C.

[0109] Hydrogen was supplied to the anode catalyst layer at a supply rate of 60 SCCM. The hydrogen was humidified so that the water vapor partial pressure was 0.4 atm.

[0110] Air was supplied to the cathode catalyst layer at a rate of 120 SCCM. The air was humidified to a water vapor partial pressure of 0.4 atm. Therefore, the water vapor partial pressure in the fuel cell was 0.4 atm during operation.

[0111] The evaluation results are shown in Figure 5. Comparative Example 1 (1) Fabrication of Fuel Cell A fuel cell was fabricated according to the following procedure.

[0112] A 1.9 mm diameter mold was prepared, and the materials for the anode catalyst layer, electrolyte layer, and cathode catalyst layer were placed in the mold in the following order and pressed to fabricate a fuel cell. (Anode catalyst layer) After placing a metal mesh to protect the end faces, 100 mg of a mixed powder of platinum-supported carbon and cesium dihydrogen phosphate in a 1:2 mass ratio was placed on top of the material for the anode catalyst layer. (Electrolyte layer) 100 mg of cesium dihydrogen phosphate was placed on top of the material for the electrolyte layer. (Cathode catalyst layer) 50 mg of a mixed powder of platinum-supported carbon and cesium dihydrogen phosphate in a 1:2 mass ratio was placed on top of the material for the electrolyte layer.

[0113] That is, except that cesium dihydrogen phosphate was used in the cathode catalyst layer instead of cesium hydrogen sulfate, a fuel cell was fabricated under the same conditions as in Example 1. (2) Operation and Evaluation of Fuel Cell The fabricated fuel cell was operated by supplying hydrogen and air to the anode catalyst layer and cathode catalyst layer under the same conditions as in Example 1, and the VI characteristics were measured by a four-terminal method using an electrochemical measurement device.

[0114] The evaluation results are shown in FIG.

[0115] 5, it was confirmed that the fuel cell of Example 1 had improved output characteristics compared to the fuel cell of Comparative Example 1.

[0116] This is thought to be because in Example 1, the use of cesium hydrogen sulfate in the cathode catalyst layer made it less likely for the platinum in the platinum-supported carbon contained in the cathode catalyst layer to be poisoned than in Comparative Example 1, thereby improving the output characteristics.

[0117] Examples of embodiments of the present invention are as follows. <1> A fuel cell comprising: a cathode catalyst layer containing a cathode-side proton-conductive ionomer; an anode catalyst layer; and an electrolyte layer containing a proton conductor, disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton-conductive ionomer contains a Group 16 element oxyacid compound; and the proton conductor contains a Group 15 element oxyacid compound. <2> The fuel cell according to <1>, wherein the Group 15 element oxyacid compound contains a phosphate-based hydrosulfate. <3> The fuel cell according to <1> or <2>, wherein the Group 15 element oxyacid compound contains cesium dihydrogenphosphate. <4> The fuel cell according to any one of <1> to <3>, wherein the Group 16 element oxyacid compound contains a sulfate-based hydrosulfate. <5> The fuel cell according to any one of <1> to <4>, wherein the Group 16 element oxyacid compound contains cesium hydrogen sulfate. <6> The fuel cell according to any one of <1> to <5>, wherein, when a surface of the electrolyte layer facing the cathode catalyst layer is defined as a first surface and a surface of the electrolyte layer facing the anode catalyst layer is defined as a second surface, the first surface and the second surface contain the Group 15 element oxygen acid compound as the proton conductor. <7> The fuel cell according to any one of <1> to <6>, wherein, when a surface of the electrolyte layer facing the cathode catalyst layer is defined as a first surface and a surface of the electrolyte layer facing the anode catalyst layer is defined as a second surface, the first surface contains the Group 16 element oxygen acid compound as the proton conductor, and the second surface contains the Group 15 element oxygen acid compound as the proton conductor. <8> The fuel cell according to any one of <1> to <7>, wherein the Group 15 element oxygen acid compound contained in the electrolyte layer is in the form of a composite. <9> The fuel cell according to any one of <1> to <8>, wherein the Group 15 element oxygen acid compound contained in the electrolyte layer is in the form of a composite with an inorganic oxide. <10> The fuel cell according to any one of <1> to <9>, further comprising an organic hydride supply device that supplies an organic hydride as a hydrogen supply substance to the anode catalyst layer.<11> A method for operating a fuel cell, the method comprising: an operating step of operating a fuel cell having a structure including: an anode catalyst layer containing a cathode-side proton-conducting ionomer; an anode catalyst layer; and an electrolyte layer containing a proton conductor disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton-conducting ionomer contains a Group 16 element oxyacid compound; and the proton conductor contains a Group 15 element oxyacid compound. <12> The method for operating a fuel cell according to <11>, wherein, in the operating step, the operating temperature of the fuel cell is set to 190°C or higher and 230°C or lower, and the water vapor partial pressure in the fuel cell is 0.3 atm or higher. <13> The method for operating a fuel cell according to <12>, further comprising, prior to the operating step, a warm-up step of raising the temperature of the fuel cell to 240°C or higher and 260°C or lower, and then raising the temperature to the operating temperature. <14> A fuel cell system including a fuel cell having a structure including: a cathode catalyst layer containing a cathode-side proton-conducting ionomer, an anode catalyst layer, and an electrolyte layer containing a proton conductor, disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton-conducting ionomer contains a Group 16 element oxyacid compound, and the proton conductor contains a Group 15 element oxyacid compound. <15> A fuel cell system including a fuel cell having a structure including: a cathode catalyst layer containing a cathode-side proton-conducting ionomer, an anode catalyst layer, and an electrolyte layer containing a proton conductor, disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton-conducting ionomer contains a sulfate-based hydrochloride, and the proton conductor contains a phosphate-based hydrochloride. This application claims priority based on Japanese Patent Application No. 2024-067025, filed with the Japan Patent Office on April 17, 2024, the entire contents of which are incorporated herein by reference.

[0118] REFERENCE SIGNS LIST 10 fuel cell 11 cathode catalyst layer 12 anode catalyst layer 13 electrolyte layer 131 first surface 132 second surface 20 fuel cell 21 diffusion layer 22 separator 23 organic hydride supply device 231 carrier gas supply device 24 organic hydride recovery device 31 first layer 32 second layer 33 third layer 34 solid line 35 two-dot chain line 36 first layer 37 second layer 38 transition layer 40 fuel cell system 41 fuel cell 42 power receiving equipment

Claims

-30-SCOPE OF THE CLAIMS

1. A fuel cell, comprising:a cathode catalyst layer including a cathode-side proton conductive ionomer;an anode catalyst layer; andan electrolyte layer including a proton conductor, the electrolyte layer being disposed between the cathode catalyst layer and the anode catalyst layer,wherein the cathode-side proton conductive ionomer includes a Group 16-element oxoacid compound, andthe proton conductor includes a Group 15-element oxoacid compound.

2. The fuel cell according to claim 1,wherein the Group 15-element oxoacid compound includes a phosphoric acid-based hydrogen acid salt.

3. The fuel cell according to claim 2,wherein the Group 15-element oxoacid compound includes cesium dihydrogen phosphate.

4. The fuel cell according to claim 1,wherein the Group 16-element oxoacid compound includes a sulfuric acid-based hydrogen acid salt.

5. The fuel cell according to claim 4,wherein the Group 16-element oxoacid compound includes cesium hydrogen sulfate.

6. The fuel cell according to any one of claims 1 to 5,wherein, when a surface of the electrolyte layer facing the cathode catalyst layer is determined as a first surface, and a surface of the electrolyte layer facing the anode catalyst layer is determined as a second surface,the first surface and the second surface include the Group 15-element oxoacid compound as the proton conductor.

7. The fuel cell according to any one of claims 1 to 5,wherein, when a surface of the electrolyte layer facing the cathode catalyst layer is determined as a first surface, and a surface of the electrolyte layer facing the anode catalyst layer is determined as a second surface,the first surface includes the Group 16-element oxoacid compound as the proton conductor, andthe second surface includes the Group 15-element oxoacid compound as the proton conductor.

8. The fuel cell according to any one of claims 1 to 5,wherein the Group 15-element oxoacid compound included in the electrolyte layer is formed into a composite.

9. The fuel cell according to any one of claims 1 to 5,wherein the Group 15-element oxoacid compound included in the electrolyte layer is formed into a composite with an inorganic oxide.

10. The fuel cell according to any one of claims 1 to 5, further comprising:an organic hydride supply device configured to supply an organic hydride, which is a hydrogen supply material, to the anode catalyst layer.

11. A method for operating a fuel cell, comprising:an operation step of operating the fuel cell, the fuel cell including:a cathode catalyst layer including a cathode-side proton conductive ionomer;an anode catalyst layer; andan electrolyte layer including a proton conductor, the electrolyte layer being disposed between the cathode catalyst layer and the anode catalyst layer,wherein the cathode-side proton conductive ionomer includes a Group 16-element oxoacid compound, andthe proton conductor includes a Group 15-element oxoacid compound.

12. The method for operating the fuel cell according to claim 11, wherein, in the operation step, an operation temperature of the fuel cell is 190°C or higher and 230°C or lower, and a water vapor partial pressure in the fuel cell is 0.3 atm or greater.

13. The method for operating the fuel cell according to claim 12, further comprising:a warming-up step of, before the operation step, setting a temperature of the fuel cell to 240 C or higher and 260 C or lower, followed by setting the temperature of the fuel cell to the operation temperature.

14. A fuel cell system comprising:a fuel cell, the fuel cell having a structure that includes:a cathode catalyst layer including a cathode-side proton conductive ionomer;an anode catalyst layer; andan electrolyte layer including a proton conductor, the electrolyte layer being disposed between the cathode catalyst layer and the anode catalyst layer,wherein the cathode-side proton conductive ionomer includes a Group 16-element oxoacid compound, andthe proton conductor includes a Group 15-element oxoacid compound.

15. A fuel cell system comprising:a fuel cell, the fuel cell having a structure that includes:a cathode catalyst layer including a cathode-side proton conductive ionomer;an anode catalyst layer; andan electrolyte layer including a proton conductor, the electrolyte layer being disposed between the cathode catalyst layer and the anode catalyst layer, wherein the cathode-side proton conductive ionomer includes a sulfuric acid-based hydrogen acid salt, andthe proton conductor includes a phosphoric acid-based hydrogen acidsalt.

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