Membrane electrode assembly and polymer electrolyte fuel cell

Abstract

The present invention provides a membrane electrode assembly which has improved cell characteristics over a long period of time. The membrane electrode assembly comprises a cathode gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and an anode gas diffusion layer. The cathode catalyst layer comprises catalyst particles that contain platinum. At least one among the cathode gas diffusion layer, the anode catalyst layer, and the anode gas diffusion layer contains at least one melamine-based compound that is a compound represented by chemical formula (1), a salt of the compound, or a polymer of the compound. In chemical formula (1), R1 to R3 are each independently an amino group, an alkyl group, an alkylamino group, a thioalkylamino group, or an alkylaminosulfonic acid group.　

Description

Membrane electrode assemblies and polymer electrolyte fuel cells

[0001] The present application relates to a membrane electrode assembly containing a melamine-based compound in a predetermined portion, and a polymer electrolyte fuel cell including the membrane electrode assembly.

[0002] Platinum or platinum alloys are used as catalysts for the cathode electrodes of polymer electrolyte fuel cells (PEFCs). The activity of these platinum and platinum alloy catalysts gradually decreases over the operating time of the PEFC. Patent Document 1 discloses a cathode electrode equipped with Pt / C catalyst particles whose surfaces are coated with a nitrogen-containing carbon film to improve the initial activity and durability of the cathode electrode. This nitrogen-containing carbon film is obtained by thermally decomposing at 700°C a coating made of a mixture of polymelamine and polydopamine coated on the surface of the Pt / C catalyst particles.

[0003] Japanese Patent Application Laid-Open No. 2022-142887

[0004] The cathode electrode in Patent Document 1 requires high-temperature treatment for fabrication. The inventors of the present application have discovered that the activity and durability of PEFCs can be improved without the need for high-temperature treatment by incorporating a melamine compound into a platinum-containing cathode catalyst layer. Under these circumstances, there is a demand for even higher activity and durability of PEFCs. An object of the present application is to provide a membrane electrode assembly that improves cell characteristics over a long period of time, and a polymer electrolyte fuel cell equipped with this membrane electrode assembly.

[0005] The membrane electrode assembly of the present application has a cathode gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and an anode gas diffusion layer, the cathode catalyst layer having catalyst particles containing platinum, and at least one portion of the cathode gas diffusion layer, the anode catalyst layer, and the anode gas diffusion layer contains one or more melamine-based compounds selected from the group consisting of a compound represented by the following chemical formula (1), a salt of this compound, and a polymer of this compound: １ From R ３ are each independently an amino group, an alkyl group, an alkylamino group, a thioalkylamino group, or an alkylaminosulfonic acid group.

[0006]

[0007] The polymer electrolyte fuel cell of the present invention has the membrane electrode assembly of the present invention, a cathode separator, and an anode separator.

[0008] The membrane electrode assembly of the present invention contains a predetermined melamine-based compound in one or more of the anode catalyst layer, the cathode gas diffusion layer, and the anode gas diffusion layer. This prevents the melamine-based compound from being excessively adsorbed onto the catalyst particles of the cathode catalyst layer, and allows the melamine-based compound to be gradually supplied to the catalyst particles of the cathode catalyst layer. This improves the cell performance of the membrane electrode assembly over a long period of time.

[0009] (a) Current-voltage curves for the MEAs of Example 1-1 and Reference Example 1 when air is supplied to the cathode electrode, (b) the current-voltage curve in the low current density region of the current-voltage curve in (a). (a) Current-voltage curves for the MEAs of Example 1-2 and Reference Example 1 when air is supplied to the cathode electrode, (b) the current-voltage curve in the low current density region of the current-voltage curve in (a). Cyclic voltammograms per unit mass of platinum for the MEAs of Example 1-1 and Reference Example 1 after air is supplied to the cathode electrode. Cyclic voltammograms per unit mass of platinum for the MEAs of Example 1-2 and Reference Example 1 after air is supplied to the cathode electrode. (a) Current-voltage curves for the MEAs of Example 1-1 and Reference Example 1 when oxygen is supplied to the cathode electrode, (b) the current-voltage curve in the low current density region of the current-voltage curve in (a).

[0033] Figure 1 shows a cyclic voltammogram per unit platinum mass of each MEA of Example 1-1 and Reference Example 1 after oxygen is supplied to the cathode electrode. Figure 2 shows a cyclic voltammogram (CV1) per unit platinum mass of each MEA of Example 2-1 and Reference Example 2 after oxygen is supplied to the cathode electrode. (a) Current-voltage curve (current-voltage curve 1) of each MEA of Example 2-1 and Reference Example 1 when oxygen is supplied to the cathode electrode, (b) a current-voltage curve in the low current density region of the current-voltage curve in (a).

[0034] Figure 3 shows another cyclic voltammogram (CV2) per unit platinum mass of each MEA of Example 2-1 and Reference Example 2. (a) Another current-voltage curve (current-voltage curve 2) of each MEA of Example 2-1 and Reference Example 1, (b) a current-voltage curve in the low current density region of the current-voltage curve in (a).

[0035] Figure 4 shows a further cyclic voltammogram (CV3) per unit platinum mass of each MEA of Example 2-1 and Reference Example 2. (a) Still another current-voltage curve (current-voltage curve 3) of each MEA of Example 2-1 and Reference Example 1, (b) a current-voltage curve in the low current density region of the current-voltage curve of (a). Cyclic voltammogram (CV3) per unit mass of platinum of each MEA of Example 2-2 and Reference Example 2. (a) A current-voltage curve (current-voltage curve 3) of each MEA of Example 2-2 and Reference Example 2, (b) a current-voltage curve in the low current density region of the current-voltage curve of (a).Cyclic voltammograms (CV3) per unit mass of platinum of MEAs of the Comparative Example and Reference Example 3. (a) Current-voltage curves (current-voltage curve 3) of MEAs of the Comparative Example and Reference Example 3. (b) Current-voltage curves in the low current density region of the current-voltage curves of (a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 1(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 2(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 5(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 8(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 10(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 12(a). Current-voltage curves in the low current density region of the current-voltage curves per unit mass of platinum of Figure 14(a). The current-voltage curve per unit mass of platinum in the low current density region of FIG. 16( a ).

[0010] The membrane electrode assembly and polymer electrolyte fuel cell of the present application will be described below based on embodiments and examples. When a range between two numerical values ​​is expressed using "to" in the present application, these two numerical values ​​are also included in the range. Duplicate explanations will be omitted as appropriate. A polymer electrolyte fuel cell of an embodiment of the present application includes a cathode separator, a cathode electrode, a solid polymer electrolyte membrane, an anode electrode, and an anode separator, in this order. A membrane electrode assembly of an embodiment of the present application includes a cathode electrode, a solid polymer electrolyte membrane (hereinafter sometimes simply referred to as the "electrolyte membrane"), and an anode electrode, in this order.

[0011] The cathode electrode includes a cathode gas diffusion layer and a cathode catalyst layer. The cathode gas diffusion layer diffuses oxygen-containing gas supplied to the cathode electrode and uniformly supplies the gas to the cathode catalyst layer. The cathode gas diffusion layer is made of a breathable carbon material, such as carbon paper made primarily of carbon fiber. The cathode catalyst layer generates water from protons, electrons, and oxygen. The cathode catalyst layer includes catalyst particles. These catalyst particles contain platinum. The catalyst particles are, for example, particles of platinum or a platinum alloy supported on a carbon support.

[0012] The solid polymer electrolyte membrane blocks the passage of electrons and gases, allowing protons to move from the anode electrode to the cathode electrode. The solid polymer electrolyte membrane is composed of a proton-conductive polymer material, such as a fluororesin having sulfonic acid groups. The cathode electrode may further include a cathode water-repellent layer between the cathode gas diffusion layer and the cathode catalyst layer. The cathode water-repellent layer can be obtained, for example, by subjecting one surface of the cathode gas diffusion layer to a water-repellent treatment.

[0013] The anode electrode includes an anode gas diffusion layer and an anode catalyst layer. The anode gas diffusion layer diffuses hydrogen-containing gas supplied to the anode electrode and uniformly supplies the gas to the anode catalyst layer. The anode gas diffusion layer is made of a breathable carbon material, such as carbon paper made mainly of carbon fiber. The anode catalyst layer decomposes hydrogen into protons and electrons. The anode catalyst layer includes catalyst particles. These catalyst particles are, for example, particles of platinum or a platinum alloy supported on a carbon support. An anode water-repellent layer may be further provided between the anode gas diffusion layer and the anode catalyst layer. The anode water-repellent layer can be obtained, for example, by treating one side of the anode gas diffusion layer to make it water-repellent.

[0014] At least one of the cathode gas diffusion layer, the anode catalyst layer, and the anode gas diffusion layer contains a melamine-based compound, which is one or more of a compound represented by the following chemical formula (1), a salt of this compound, and a polymer of this compound. １ From R ３ are each independently an amino group, an alkyl group, an alkylamino group, a thioalkylamino group, or an alkylaminosulfonic acid group.

[0015]

[0016] The melamine-based compound may be contained in the cathode gas diffusion layer or the like in the form of melamine cyanurate or the like. When the melamine-based compound is a salt, the melamine-based compound is a salt having a compound represented by chemical formula (1) as the cation. The number of carbon atoms in the alkyl group is preferably 1 to 16, and more preferably 1 to 8. The number of carbon atoms in the alkylamino group, thioalkylamino group, and alkylaminosulfonic acid group is preferably 1 to 16, and more preferably 1 to 12, and even more preferably 1 to 8.

[0017] The melamine-based compound contained in the cathode gas diffusion layer is gradually supplied to the catalyst particles of the cathode catalyst layer. The melamine-based compound contained in the anode catalyst layer passes through the solid polymer electrolyte membrane and is gradually supplied to the catalyst particles of the cathode catalyst layer. The melamine-based compound contained in the anode gas diffusion layer passes through the cathode catalyst layer and the solid polymer electrolyte membrane and is gradually supplied to the catalyst particles of the cathode catalyst layer. This prevents the melamine-based compound from being excessively adsorbed onto the catalyst particles of the cathode catalyst layer.

[0018] As a result, the cell performance of a membrane electrode assembly containing a melamine-based compound in at least one of the cathode gas diffusion layer, anode catalyst layer, and anode gas diffusion layer is improved over a long period of time compared to the cell performance of a membrane electrode assembly that does not contain a melamine-based compound or the cell performance of a membrane electrode assembly that contains a melamine-based compound only in the cathode catalyst layer. Examples of melamine-based compounds include acetoguanamine, melamine monomer, and octylmelamine. It is preferred that one or more of these melamine-based compounds be contained in at least one of the cathode gas diffusion layer, anode catalyst layer, and anode gas diffusion layer.

[0019] The mass ratio of the melamine-based compound to the mass of platinum contained in the cathode catalyst layer is preferably 0.5% to 20%, more preferably 1% to 15%, and even more preferably 2% to 10%. The melamine-based compound does not include a calcined melamine product. A calcined melamine product is a substance containing carbon as its main component, obtained by calcining a melamine-based compound at, for example, around 700°C. Even if a calcined melamine product is contained in the cathode gas diffusion layer, anode catalyst layer, or anode gas diffusion layer, this calcined product is not supplied to the catalyst particles of the cathode catalyst layer.

[0020] Alternatively, only the cathode gas diffusion layer may contain a melamine-based compound, or only the anode catalyst layer may contain a melamine-based compound. When the anode catalyst layer or the anode gas diffusion layer contains a melamine-based compound, a solid polymer electrolyte membrane through which the melamine-based compound passes is used. However, a general solid polymer electrolyte membrane can be used instead of a special solid polymer electrolyte membrane. The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to the following examples.

[0021] (Example 1: Supply of a melamine-based compound from a cathode gas diffusion layer to a cathode catalyst layer) 430 mg of 1-propanol (FUJIFILM Wako Pure Chemical Industries, Ltd. (hereinafter the same)), 50 mg of platinum catalyst particles (Tanaka Kikinzoku Kogyo K.K., TEC10V30E) in which platinum is supported on a carbon support and which constitute a cathode catalyst, and 140 mg of ionomer (FUJIFILM Wako Pure Chemical Industries, Ltd., DE2021) were mixed under a nitrogen atmosphere to obtain a cathode catalyst dispersion. The ratio of the mass of the ionomer to the total mass of the carbon support in the platinum catalyst particles was 0.8. This cathode catalyst dispersion was applied to obtain a cathode catalyst sheet. A 10 mm square piece was cut out from this cathode catalyst sheet to form a cathode catalyst layer.

[0022] An anode catalyst layer was also prepared using the same procedure and ionomer ratio as the cathode catalyst layer, except that platinum catalyst particles (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) were used, in which platinum was supported on a carbon support. An electrolyte membrane (Nafion 212, manufactured by Chemours, Inc.) measuring 7 cm in length, 7 cm in width, and 0.051 mm in thickness was sandwiched between the cathode catalyst layer and the anode catalyst layer, and the resulting mixture was hot-pressed to obtain a laminate.

[0023] A carbon paper (SGL Carbon, 22BB) with a water-repellent layer on one side, measuring 11.5 mm in length, 11.5 mm in width, and 0.215 mm in thickness, was attached to the cathode side of this laminate, with the water-repellent layer facing the cathode catalyst layer. This carbon paper became the cathode gas diffusion layer (cathode GDL). The same carbon paper was attached to the anode side, with the water-repellent layer facing the anode catalyst layer, to produce the MEA of Reference Example 1. This carbon paper became the cathode gas diffusion layer (cathode GDL). The platinum weight of the cathode catalyst layer of the MEA of Reference Example 1 was 0.161 mg. Ｐｔ cm －２ (MEA when evaluated in air) or 0.171 mg Ｐｔ cm －２ (MEA when evaluated with oxygen).

[0024] The water-repellent layer (MPL) side of the cathode GDL of the MEA of Reference Example 1 was impregnated with 50 μL of a 1.5 mM acetone solution of acetoguanamine (AG) (Tokyo Chemical Industry Co., Ltd.), a melamine-based compound, and dried to obtain an MEA of Example 1-1 containing AG in the cathode GDL. The platinum weight of the cathode catalyst layer of the MEA of Example 1-1 was 0.175 mg Ｐｔ cm －２ (MEA when evaluated in air) or 0.177 mg Ｐｔ cm －２ (MEA when evaluated with oxygen) The ratio of the mass of AG to the mass of platinum in the platinum catalyst particles contained in the cathode catalyst layer of the MEA of Example 1-1 was 5.4%.

[0025] An MEA of Example 1-2 containing MM in the cathode GDL was obtained in the same manner as in the preparation of the MEA of Example 1-1, except that 50 μL of a 1.5 mM solution containing melamine monomer (MM), a melamine-based compound (Tokyo Chemical Industry Co., Ltd. (hereinafter the same)), in a solvent containing a 4:1 volumetric mixture of acetone and water was used instead of the AG solution. The platinum weight of the cathode catalyst layer of the MEA of Example 1-2 was 0.144 mg Ｐｔ cm －２ The ratio of the mass of MM to the mass of platinum in the platinum catalyst particles contained in the cathode catalyst layer of the MEA of Example 1-2 was 6.6%.

[0026] Nitrogen gas was then supplied to the cathode electrode to achieve nitrogen saturation, the supply of nitrogen gas was stopped, and 70 sccm of hydrogen gas was supplied to the anode electrode while a sweep rate of 50 mV / sec was performed for 5 cycles to evaluate the cyclic voltammetry of each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1. Next, under power generation test conditions (hereinafter sometimes referred to as "first power generation test conditions") of a bubbler temperature of 73°C, a piping temperature of 90°C, and a cell temperature of 78°C (RH 81%), a power generation test of each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1 was carried out in the following procedure.

[0027] Specifically, the initial current-voltage characteristics of the MEA were evaluated while supplying 500 sccm of air to the cathode electrode and 200 sccm of pure hydrogen gas to the anode electrode. Next, while continuing to supply these gases to the MEA, constant voltage operation at 0.4 V was performed for 4 hours, and the current-voltage characteristics of the MEA were evaluated again. Figure 1(a) shows the current-voltage curves of the MEA of Example 1-1 ("TEC10V30E (AG 75 nmol GDL)-Air" (same as in Figure 3)) and the MEA of Reference Example 1 ("TEC10V30E (normal GDL)-Air" (same as in Figures 2(a), 3, and 4)) during this re-evaluation. Figure 1(b) shows the low current density region of the current-voltage curve of Figure 1(a). Figure 17 shows the low current density region of the current-voltage curve per unit mass of platinum of Figure 1(a).

[0028] FIG. 2(a) shows current-voltage curves of the MEA of Example 1-2 ("TEC10V30E (MM 0.05 GDL-1st)" in the figure (the same applies to FIG. 4)) and the MEA of Reference Example 1. FIG. 2(b) shows the low current density region of the current-voltage curve of FIG. 2(a). FIG. 18 shows the low current density region of the current-voltage curve per unit mass of platinum in FIG. 2(a). As shown in FIGS. 1(a), 1(b), 17, 2(a), 2(b), and 18, the cell voltages of the MEAs of Examples 1-1 and 1-2, in which the cathode GDL was impregnated with a melamine-based compound, were higher than the cell voltage of the MEA of Reference Example 1, in which the cathode GDL was not impregnated with a melamine-based compound, particularly in the low current density region.

[0029] Thereafter, nitrogen gas was supplied to the cathode electrode to saturate it with nitrogen, the supply of nitrogen gas was stopped, and 70 sccm of hydrogen gas was supplied to the anode electrode, while a sweep rate of 50 mV / sec was used for 5 cycles to evaluate the cyclic voltammetry of each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1. FIG. 3 shows the cyclic voltammograms per unit platinum mass of the MEA of Example 1-1 and the MEA of Reference Example 1. FIG. 4 shows the cyclic voltammograms per unit platinum mass of the MEA of Example 1-2 and the MEA of Reference Example 1.

[0030] As shown in Figures 3 and 4, the waveforms of the cyclic voltammograms of the MEAs of Examples 1-1 and 1-2 are clearly different from the waveform of the cyclic voltammogram of the MEA of Reference Example 1. This change in waveform is thought to be the result of an appropriate amount of melamine-based compound being adsorbed onto the platinum in the cathode catalyst layer. In other words, this indicates that the melamine-based compound impregnated into the cathode GDL is being supplied to the cathode catalyst layer. From the above, it was possible to improve cell characteristics by impregnating the cathode GDL with a melamine-based compound.

[0031] Next, another example will be described in which oxygen was supplied to the cathode electrode instead of air. First, nitrogen gas was supplied to the cathode electrode of a new MEA to saturate it with nitrogen. The nitrogen gas supply was then stopped, and 70 sccm of hydrogen gas was supplied to the anode electrode. Cyclic voltammetry was evaluated for each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1 at a sweep rate of 50 mV / sec for five cycles. Then, under the first power generation test conditions, 200 sccm of oxygen was supplied to the cathode electrode and 200 sccm of pure hydrogen gas was supplied to the anode electrode, and the initial current-voltage characteristics of each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1 were evaluated. Next, constant voltage operation at 0.54 V was performed for four hours, and the current-voltage characteristics of the MEA were evaluated again.

[0032] FIG. 5( a) shows current-voltage curves of the MEA of Example 1-1 ("TEC10V30E (AG 75 nmol GDL)" in the figure) and the MEA of Reference Example 1 ("TEC10V30E (normal GDL)" in the figure) when the current-voltage characteristics were evaluated again under conditions in which oxygen was supplied to the cathode electrode. FIG. 5( b) shows the low current density region of the current-voltage curve of FIG. 5( a). FIG. 19 shows the low current density region of the current-voltage curve per unit mass of platinum in FIG. 5( a). As shown in FIGS. 5( a), 5( b), and 19, the cell voltages of the MEAs of Examples 1-1 and 1-2, in which the cathode GDL was impregnated with a melamine-based compound, were higher than the cell voltage of the MEA of Reference Example 1, in which the cathode GDL was not impregnated with a melamine-based compound, particularly in the low current density region.

[0033] Thereafter, nitrogen gas was supplied to the cathode electrode to saturate it with nitrogen, the supply of nitrogen gas was stopped, and 70 sccm of hydrogen gas was supplied to the anode electrode while a sweep rate of 50 mV / sec was performed for 5 cycles to evaluate the cyclic voltammetry of each of the MEAs of Example 1-1, Example 1-2, and Reference Example 1. Figure 6 shows the cyclic voltammograms per unit mass of platinum of the MEA of Example 1-1 ("Pt / V 75 nmol AG on GDL-C after" in the figure) and the MEA of Reference Example 1 ("Pt / V-C after" in the figure).

[0034] 6, the waveform of the cyclic voltammogram for the MEA of Example 1-1 is clearly different from that of the MEA of Reference Example 1. This change in waveform is thought to be the result of the melamine-based compound being adsorbed into the cathode catalyst layer. In other words, even when power is generated by supplying oxygen to the cathode electrode, impregnating the cathode GDL with a melamine-based compound ensures that the melamine-based compound is supplied to the cathode catalyst layer, thereby improving cell characteristics.

[0035] Example 2: Supply of a melamine-based compound from an anode catalyst layer to a cathode electrode. 344 μL of water, 246 μL of 1-propanol, 50 μL of ethylene glycol (FUJIFILM Wako Pure Chemical Industries, Ltd. (hereinafter the same)), 50 mg of platinum catalyst particles (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10V30E) constituting a cathode catalyst, in which platinum is supported on a carbon support, and 147 mg of ionomer (FUJIFILM Wako Pure Chemical Industries, Ltd., DE2020) were mixed, and the mixture was subjected to ultrasonic dispersion and stirring to obtain a cathode catalyst ink. This cathode catalyst ink was applied to a PTFE sheet (Nitto Denko Corporation (hereinafter the same)) to a thickness of 140 μm and vacuum dried at 100° C. to obtain a cathode catalyst sheet. This cathode catalyst sheet was cut to a length of 10 mm and a width of 10 mm to obtain a cathode catalyst layer. The ratio of the mass of the ionomer to the total mass of the carbon support in the platinum catalyst particles was 0.83.

[0036] MM and nonafluorobutane-1-sulfonic acid (PFBS) (Merck Co., Ltd.) were contained in equimolar amounts, with the total amount being 3.81 mg mL －１ 328 μL of this aqueous solution, 241 μL of 1-propanol, 50 μL of ethylene glycol, and 116 mg of ionomer (Fujifilm Wako Pure Chemical Industries, Ltd., DE2020) were added to 50 mg of platinum catalyst particles (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) in which platinum was supported on a carbon support, followed by ultrasonic dispersion and stirring to obtain an anode catalyst ink.

[0037] This anode catalyst ink was applied to a PTFE sheet to a thickness of 100 μm and vacuum dried at 100° C. to obtain an anode catalyst sheet. This anode catalyst sheet was cut into a length of 10 mm and a width of 10 mm to obtain an anode catalyst layer. The ratio of the total mass of MM and PFBS to the mass of platinum in the platinum catalyst particles contained in the anode catalyst layer was 0.053.

[0038] Carbon paper (Toray Industries, Inc., TGP-H-060) measuring 11 mm in length, 11 mm in width, and 0.19 mm in thickness that served as the cathode GDL, a cathode catalyst layer, an electrolyte membrane, an anode catalyst layer, and carbon paper (SGL Carbon Co., Ltd., 22BB) with a water-repellent layer on one side that served as the anode GDL were stacked in this order to obtain an MEA of Example 2-1 that included a cathode electrode composed of the cathode GDL and the cathode catalyst layer, and an anode electrode composed of the electrolyte membrane, the anode catalyst layer, and the anode GDL. The platinum content of the cathode catalyst layer of the MEA of Example 2-1 was 0.203 mg Ｐｔ cm －２ The ratio of the total mass of MM and PFBS to the mass of platinum in the platinum catalyst particles contained in the cathode catalyst layer of the MEA of Example 2-1 was 0.062.

[0039] An MEA of Reference Example 2, which did not contain a melamine-based compound in the anode catalyst layer, was obtained in the same manner as in Example 2-1, except that an anode catalyst ink containing neither MM nor PFBS was used. The platinum weight in the cathode catalyst layer of the MEA of Reference Example 2 was 0.202 mg. Ｐｔ cm －２ Next, nitrogen gas was supplied to the cathode electrode to saturate it with nitrogen, and the supply of nitrogen gas was stopped. Then, while supplying 70 sccm of hydrogen gas to the anode electrode, the cyclic voltammetry of each of the MEAs of Example 2-1 and Reference Example 2 was evaluated at a sweep rate of 50 mV / sec for 5 cycles.

[0040] Then, under power generation test conditions (hereinafter sometimes referred to as "second power generation test conditions") of a bubbler temperature of 73°C, a pipe temperature of 85°C, and a cell temperature of 80°C (RH 75%), a power generation test was carried out for each of the MEAs of Example 2-1 and Reference Example 2, in the following procedure. First, while supplying 209 sccm of oxygen gas to the cathode electrode and 209 sccm of pure hydrogen gas to the anode electrode, constant voltage operation at 0.5 V for 5 hours, constant voltage operation at 0.4 V for 2.5 hours, and constant voltage operation at 0.3 V for 2.5 hours were carried out successively, and the initial current-voltage characteristics of the MEA were then evaluated.

[0041] Nitrogen gas was then supplied to the cathode and anode electrodes to achieve nitrogen saturation, heating of the MEA and piping was stopped to stop operation of the MEA, and then the MEA and piping were heated again. Under the second power generation test conditions, 70 sccm of hydrogen gas was supplied to the anode electrode, and the cyclic voltammetry of each MEA of Example 2-1 and Reference Example 2 was evaluated at a sweep rate of 50 mV / sec for 5 cycles. Figure 7 shows the cyclic voltammograms (CV1) per unit mass of platinum for the MEA of Example 2-1 ("TEC10V30E (MM-PFBS-impregnated anode)" (same in Figures 8(a) to 12(b) and Figures 20 to 22)) and the MEA of Reference Example 2 ("TEC10V30E (normal anode)" (same in Figures 8(a) to 13 and Figures 20 to 23)).

[0042] 7, the waveform of the cyclic voltammogram for the MEA of Example 2-1 is clearly different from that of the MEA of Reference Example 2. This change in waveform is thought to be the result of the melamine-based compound being adsorbed onto the cathode catalyst layer. In other words, this indicates that the melamine-based compound contained in the anode catalyst layer is supplied to the cathode catalyst layer via the electrolyte membrane.

[0043] Next, while supplying 209 sccm of oxygen gas to the cathode electrode and 209 sccm of pure hydrogen gas to the anode electrode, constant voltage operation was performed at 0.5 V for 10 minutes, constant voltage operation at 0.4 V for 10 minutes, and constant voltage operation at 0.3 V for 10 minutes, and then the current-voltage characteristics of each of the MEAs of Example 2-1 and Reference Example 2 were evaluated again. Figure 8(a) shows the current-voltage curves (current-voltage curve 1) of the MEAs of Example 2-1 and Reference Example 2 at this time. Figure 8(b) shows the low current density region of the current-voltage curve of Figure 8(a). Figure 20 shows the low current density region of the current-voltage curve per unit mass of platinum of Figure 8(a). As shown in Figures 8(a), 8(b), and 20, the cell voltage of the MEA of Example 2-1, in which the anode catalyst layer was impregnated with a melamine-based compound, was higher than the cell voltage of the MEA of Reference Example 2, in which the anode catalyst layer was not impregnated with a melamine-based compound, particularly in the low current density region.

[0044] Then, each MEA of Example 2-1 and Reference Example 2 was left under overhumidified conditions for 3 hours, dried with dry nitrogen, and again subjected to the second power generation test conditions, where 70 sccm of hydrogen gas was supplied to the anode electrode, and the cyclic voltammetry of each MEA of Example 2-1 and Reference Example 2 was evaluated at a sweep rate of 50 mV / sec for 5 cycles. Figure 9 shows the cyclic voltammogram (CV2) per unit mass of platinum for each MEA of Example 2-1 and Reference Example 2 at this time.

[0045] 9, the waveform of the cyclic voltammogram for the MEA of Example 2-1 is clearly different from that of the MEA of Reference Example 2. This change in waveform is thought to be the result of the melamine-based compound being adsorbed onto the cathode catalyst layer. In other words, this indicates that the melamine-based compound contained in the anode catalyst layer is supplied to the cathode catalyst layer via the electrolyte membrane.

[0046] Next, while supplying 209 sccm of oxygen gas to the cathode electrode and 209 sccm of pure hydrogen gas to the anode electrode, constant voltage operation was performed at 0.5 V for 10 minutes, constant voltage operation at 0.4 V for 10 minutes, and constant voltage operation at 0.3 V for 10 minutes, and then the current-voltage characteristics of each MEA of Example 2-1 and Reference Example 2 were evaluated. FIG. 10(a) shows the current-voltage curves (current-voltage curve 2) of each MEA of Example 2-1 and Reference Example 2 at this time. FIG. 10(b) shows the low current density region of the current-voltage curve of FIG. 10(a). FIG. 21 shows the low current density region of the current-voltage curve per unit mass of platinum of FIG. 10(a). As shown in Figures 10(a), 10(b), and 21, the cell voltage of the MEA of Example 2-1, in which the anode catalyst layer was impregnated with a melamine-based compound, was higher than the cell voltage of the MEA of Reference Example 2, in which the anode catalyst layer was not impregnated with a melamine-based compound, particularly in the low current density region.

[0047] Then, each MEA of Example 2-1 and Reference Example 2 was left under overhumidified conditions for 3 hours, dried with dry nitrogen, and again subjected to the second power generation test conditions, where 70 sccm of hydrogen gas was supplied to the anode electrode, and the cyclic voltammetry of each MEA of Example 2-1 and Reference Example 2 was evaluated at a sweep rate of 50 mV / sec for 5 cycles. Figure 11 shows the cyclic voltammograms per unit mass of platinum of each MEA of Example 2-1 and Reference Example 2 at this time (hereinafter, the cyclic voltammogram per unit mass of platinum evaluated under such conditions may be referred to as "CV3").

[0048] 11 , the waveform of the cyclic voltammogram for the MEA of Example 2-1 is clearly different from that of the MEA of Reference Example 2. This change in waveform is thought to be the result of the melamine-based compound being adsorbed onto the cathode catalyst layer. In other words, this indicates that the melamine-based compound contained in the anode catalyst layer is supplied to the cathode catalyst layer via the electrolyte membrane.

[0049] Next, while supplying 209 sccm of oxygen gas to the cathode electrode and 209 sccm of pure hydrogen gas to the anode electrode, constant voltage operation was performed at 0.5 V for 10 minutes, constant voltage operation at 0.4 V for 10 minutes, and constant voltage operation at 0.3 V for 10 minutes, and then the current-voltage characteristics of each MEA of Example 2-1 and Reference Example 2 were evaluated. FIG. 12(a) shows the current-voltage curve (current-voltage curve 3) of each MEA of Example 2-1 and Reference Example 2 at this time. FIG. 12(b) shows the low current density region of the current-voltage curve of FIG. 12(a). FIG. 22 shows the low current density region of the current-voltage curve per unit mass of platinum of FIG. 12(a).

[0050] 12(a), 12(b), and 22, the cell voltage of the MEA of Example 2-1, in which the anode catalyst layer was impregnated with a melamine-based compound, was higher than the cell voltage of the MEA of Reference Example 2, in which the anode catalyst layer was not impregnated with a melamine-based compound, particularly in the low current density region. As described above, by impregnating the anode catalyst layer with a melamine-based compound, the melamine-based compound is continuously supplied from the anode catalyst layer to the cathode catalyst layer via the electrolyte membrane, and the cell characteristics of the MEA can be improved over a long period of time.

[0051] The method for incorporating a melamine-based compound into the anode catalyst layer is not limited to this. A melamine-based compound may be supported on catalyst powder before preparing the anode catalyst ink. An example of this is described below. 250 mg of platinum catalyst particles (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) in which platinum is supported on a carbon support were suspended in a mixture of 2-propanol and a 1 mM aqueous solution of PFBS containing 50 μmol of octylmelamine (OM) (Koyo Chemical Co., Ltd.). The suspension was refluxed, filtered, washed, and dried to obtain OM-supported catalyst particles.

[0052] 450 mg of a liquid mixture of water and 1-propanol in a mass ratio of 3:1 and 110 mg of ionomer (FUJIFILM Wako Pure Chemical Industries, Ltd., DE2020) were added to 50 mg of the OM-supported catalyst particles, followed by ultrasonic dispersion and stirring to obtain an anode catalyst ink. This anode catalyst ink was applied to a PTFE sheet (manufactured by Nitto Denko Corporation) to a thickness of 120 μm and vacuum dried at 100°C to obtain an anode catalyst sheet. This anode catalyst sheet was cut to a length of 10 mm and a width of 10 mm to obtain an anode catalyst layer.

[0053] Thereafter, an MEA of Example 2-2 containing OM in the anode catalyst layer was obtained in the same manner as in the preparation procedure for the MEA of Example 2-1. The ratio of the mass of OM to the mass of platinum in the platinum catalyst particles contained in the cathode catalyst layer of the MEA of Example 2-2 was 0.029. CV3 of the MEA of Example 2-2 was obtained in the same manner as in the evaluation of each MEA of Example 2-1 and Reference Example 2. Figure 13 shows the cyclic voltammograms (CV3) per unit mass of platinum for the MEA of Example 2-2 ("TEC10V30E (OM-impregnated anode" in the figure)) and the MEA of Reference Example 2 at this time.

[0054] 13, the waveform of the cyclic voltammogram for the MEA of Example 2-2 is clearly different from that of the MEA of Reference Example 2. This change in waveform is thought to be the result of the melamine-based compound being adsorbed into the cathode catalyst layer. In other words, this indicates that even when a melamine-based compound with relatively high fat solubility, such as OM, is impregnated into the anode catalyst layer, this melamine-based compound is supplied to the cathode catalyst layer.

[0055] The current-voltage characteristics of the MEAs of Example 2-2 and Reference Example 2 were evaluated in the same manner as in the evaluation of the MEAs of Example 2-1 and Reference Example 2. FIG. 14(a) shows the current-voltage curves (current-voltage curve 3) of the MEAs of Example 2-2 and Reference Example 2. FIG. 14(b) shows the low current density region of the current-voltage curve of FIG. 14(a). FIG. 23 shows the low current density region of the current-voltage curve per unit mass of platinum of FIG. 14(a). As shown in FIGS. 14(a), 14(b), and 23, the cell voltage of the MEA of Example 2-2, in which the anode catalyst layer was impregnated with a melamine-based compound, was higher than the cell voltage of the MEA of Reference Example 2, in which the anode catalyst layer was not impregnated with a melamine-based compound, particularly in the low current density region.

[0056] (Comparative Example: Cathode Catalyst Layer Containing a Melamine-Based Compound) A comparative MEA was obtained, which included a cathode catalyst layer impregnated with MM-PFBS, a melamine-based compound, and an anode catalyst layer not impregnated with a melamine-based compound, in the same manner as in the preparation of the MEA of Example 2-1, except that the anode catalyst layer and cathode catalyst layer of Example 2-1 were swapped. The ratio of the mass of the ionomer to the total mass of the carbon support in the platinum catalyst particles contained in this anode catalyst layer was 0.83. Furthermore, the ratio of the total mass of MM and PFBS to the mass of platinum in the platinum catalyst particles contained in the cathode catalyst layer of the comparative MEA was 0.053. The platinum weight per unit area of ​​the anode catalyst layer of the comparative MEA was 0.251 mg Ｐｔ cm －２ It was.

[0057] Further, an MEA of Reference Example 3 was obtained, which had an anode catalyst layer and a cathode catalyst layer that were not impregnated with a melamine-based compound, in the same manner as in the MEA of Reference Example 2, except that the anode catalyst layer and the cathode catalyst layer of Reference Example 2 were interchanged. The platinum weight of the anode catalyst layer of the MEA of Reference Example 3 was 0.260 mg Ｐｔ cm －２ CV3 of the MEAs of the comparative example and reference example 3 was obtained in the same manner as in the evaluation of the MEAs of Example 2-1 and Reference Example 2.

[0058] FIG. 15 shows cyclic voltammograms (CV3) per unit mass of platinum for the MEA of the comparative example ("TEC10E50E (MM-PFBS-impregnated cathode)" in the figure (same in FIGS. 16(a), 16(b), and 24)) and the MEA of Reference Example 3 ("TEC10E50E (normal cathode)" in the figure (same in FIGS. 16(a), 16(b), and 24)). As shown in FIG. 15, the waveform of the cyclic voltammogram of the MEA of the comparative example is clearly different from that of the MEA of Reference Example 3. This change in waveform is thought to be due to the melamine-based compound contained in the cathode catalyst layer being adsorbed onto the platinum in the cathode catalyst layer.

[0059] Furthermore, the current-voltage characteristics of the MEAs of Comparative Example and Reference Example 3 were evaluated in the same manner as in the evaluation of the MEAs of Example 2-1 and Reference Example 2. Figure 16(a) shows the current-voltage curves (current-voltage curve 3) of the MEAs of Comparative Example and Reference Example 3. Figure 16(b) shows the low current density region of the current-voltage curve of Figure 16(a). Figure 24 shows the low current density region of the current-voltage curve per unit mass of platinum of Figure 16(a).

[0060] 16(a), 16(b), and 24, the cell voltage of the MEA of the comparative example, in which the cathode catalyst layer was impregnated with a melamine-based compound, was lower than the cell voltage of the MEA of Reference Example 3, in which the melamine-based compound was not impregnated. It can be seen that when the cathode catalyst layer is impregnated with a melamine-based compound, an excess of the melamine-based compound is supplied to the platinum in the cathode catalyst layer, inhibiting the catalytic function of the platinum, and the cell voltage of the MEA does not increase across the entire current density range.

Claims

1. A membrane electrode assembly having a cathode gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and an anode gas diffusion layer, wherein the cathode catalyst layer comprises catalyst particles containing platinum, and at least one portion of the cathode gas diffusion layer, the anode catalyst layer, and the anode gas diffusion layer contains one or more melamine-based compounds selected from the group consisting of a compound represented by the following chemical formula (1), a salt of this compound, and a polymer of this compound: In chemical formula (1), R １ From R ３ are each independently an amino group, an alkyl group, an alkylamino group, a thioalkylamino group, or an alkylaminosulfonic acid group.

2. A membrane electrode assembly according to claim 1, wherein only the cathode gas diffusion layer contains the melamine-based compound.

3. A membrane electrode assembly according to claim 1, wherein only the anode catalyst layer contains the melamine-based compound.

4. A membrane electrode assembly according to claim 1, wherein the mass ratio of the melamine-based compound to the mass of platinum contained in the cathode catalyst layer is 0.5% to 20%.

5. A membrane electrode assembly according to any one of claims 1 to 4, wherein the melamine-based compound is one or more of acetoguanamine, melamine monomer, and octylmelamine.

6. A polymer electrolyte fuel cell comprising: the membrane electrode assembly of any one of claims 1 to 4; a cathode separator; and an anode separator.

7. A polymer electrolyte fuel cell comprising the membrane electrode assembly of claim 5, a cathode separator, and an anode separator.

Images