JP2018163843A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell capable of reducing the amount of platinum used and reducing the cost, and suppressing the decrease in power generation efficiency due to the poisoning of platinum by an ionomer. A membrane-electrode assembly (MEA) 1 having an electrolyte membrane 4, an anode 2 provided on one surface of the electrolyte membrane 4, and a cathode 3 provided on the other surface of the electrolyte membrane 4 is provided. The anode 2 includes a supported catalyst in which platinum is supported on a solid carbon carrier, and has an anode-side catalyst layer 2 that is arranged to face the electrolyte membrane 4, and the cathode 3 is such that platinum is supported on a hollow carbon carrier. A fuel cell including a supported catalyst and having a cathode-side catalyst layer 3 arranged opposite to an electrolyte membrane 4. [Selection diagram] Figure 1

Description

  The present invention relates to a fuel cell.

  In a fuel cell (system), a fuel gas typified by hydrogen gas and an oxidizing gas typified by air are supplied to the fuel cell, and electric power is generated by a power generation reaction (water generation reaction) between the fuel gas and the oxidizing gas. . Various types of fuel cells have been developed. For example, there are no problems such as electrolyte dissipation and retention, and the polymer electrolyte fuel cell has advantages such as startup at room temperature and extremely fast startup time. (PEFC: Polymer Electrolyte Fuel Cells), etc. Specifically, a plurality of fuel cells (single cells) stacked to obtain a high voltage (fuel cell stack) is a moving body such as an automobile. Is being adopted.

  As the single cell, for example, an MEA (membrane-electrode assembly) composed of an electrolyte membrane, an anode provided on one surface and a cathode provided on the other surface is sandwiched by separators. The anode and the cathode usually have a catalyst layer formed on the electrolyte membrane side and a catalyst layer formed on the separator side. If attention is paid to the positional relationship between the electrolyte membrane and the catalyst layer in such a configuration, the catalyst layers are disposed on both surfaces of the MEA electrolyte membrane. As the catalyst layer, a support made of carbon or the like and a catalyst metal such as platinum (Pt) is widely used, and the support made of hollow particles or solid particles is known ( For example, see Patent Document 1).

2008-171720

  By the way, in the case of a supported catalyst in which platinum is supported on a hollow carbon carrier, platinum adheres not only to the outer surface of the hollow carbon carrier but also to the inner surface which is a hollow part, but the hollow part hardly contributes to power generation. Therefore, the platinum adhering to it is wasted and increases the cost. On the other hand, when a supported catalyst in which platinum is supported on a solid carbon support is used, platinum tends to be poisoned by an ionomer on the surface of the catalyst layer, and power generation efficiency tends to be reduced.

  Therefore, the present invention has been made in view of such circumstances, and can reduce the amount of platinum used to reduce the cost, and suppress the decrease in power generation efficiency due to the poisoning of platinum by ionomers. An object of the present invention is to provide a fuel cell that can be used.

  In order to solve the above problems, a fuel cell according to an aspect of the present invention includes an MEA having an electrolyte membrane, an anode provided on one surface of the electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane. The anode includes a supported catalyst in which platinum is supported on a solid carbon support and has an anode-side catalyst layer disposed opposite to the electrolyte membrane, and the cathode is supported in which platinum is supported on a hollow carbon support. It has a cathode side catalyst layer that contains a catalyst and is arranged opposite to the electrolyte membrane.

  In general, since the potential is relatively low on the anode side in the MEA of the fuel cell, platinum in the anode side catalyst layer tends not to be poisoned by ionomers. Therefore, even if a solid carbon carrier is used as the catalyst carrier of the anode side catalyst layer, platinum is hardly poisoned by the ionomer, and thus a reduction in power generation efficiency can be prevented. In addition, when a solid carbon carrier is used, platinum hardly enters the inside of the carrier, and platinum can be supported on the outer surface, which greatly contributes to power generation efficiency, thereby reducing the amount of platinum used. Cost can be reduced.

  On the other hand, since the potential is relatively high on the cathode side of the MEA of the fuel cell, platinum in the cathode side catalyst layer tends to be easily poisoned by ionomers. On the other hand, when a hollow carbon carrier is used as the catalyst carrier of the cathode side catalyst layer, platinum enters the hollow portion (inside) of the hollow carbon carrier and is supported, so when a solid carbon carrier is used. In comparison, the poisoning of platinum by ionomers can be reduced, thereby suppressing a decrease in power generation efficiency.

  According to the present invention, a solid carbon carrier and a hollow carbon carrier are used in combination as the platinum carrier in the catalyst layer, that is, more specifically, the anode side catalyst layer has platinum supported on the solid carbon carrier. By including a supported catalyst, and the cathode side catalyst layer includes a supported catalyst in which platinum is supported on a hollow carbon support, the amount of platinum used can be reduced and the cost can be reduced. It is possible to suppress a decrease in power generation efficiency due to poison.

It is a schematic sectional drawing which shows partially an example of a structure of MEA in the polymer electrolyte fuel cell which concerns on 1 aspect of this invention. (A) And (B) is a schematic sectional drawing which shows an example of the structure of the supported catalyst 5a in the anode side catalyst layer 2, and the supported catalyst 5b in the cathode side catalyst layer 3, respectively. Platinum in the case where the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a and the supported catalyst 5b in which platinum Pt is supported on the hollow carbon support 7b are used for the anode side catalyst layer 2. It is a graph which shows the change of the electrochemical surface area (ECSA) of platinum Pt with respect to the fabric weight of Pt. When the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and the supported catalyst 5b in which platinum Pt is supported on the hollow carbon support 7b is used. It is a graph which shows the change of the cell voltage with respect to the current density in a case. When the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and the supported catalyst 5b in which platinum Pt is supported on the hollow carbon support 7b is used. It is a graph which shows the change of the cell voltage in the target current density with respect to the electrochemical surface area (ECSA) of platinum Pt in the case. When the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and the supported catalyst 5b in which platinum Pt is supported on the hollow carbon support 7b is used. It is a graph which shows the change of the anode overvoltage with respect to the electrochemical surface area (ECSA) of platinum Pt in the case.

  Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention only to the embodiments. The present invention can be variously modified without departing from the gist thereof. Furthermore, those skilled in the art can employ embodiments in which the elements described below are replaced with equivalent ones, and such embodiments are also included in the scope of the present invention. Furthermore, positional relationships such as up, down, left, and right shown as needed are based on the display shown unless otherwise specified. Furthermore, various dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a schematic cross-sectional view partially showing an example of the configuration of an MEA in a polymer electrolyte fuel cell (PEFC) according to an aspect of the present invention. The MEA 1 includes an anode-side catalyst layer 2 in the anode and a cathode-side catalyst layer 3 in the cathode, and an electrolyte membrane 4 interposed between them and including an ion conductive solid electrolyte 6. As described above, the anode-side catalyst layer 2 and the cathode-side catalyst layer 3 are disposed to face the one surface side and the other surface side (both surface sides) of the electrolyte membrane 4, respectively. The anode side catalyst layer 2 includes a supported catalyst 5 a and an ion conductive solid electrolyte 6, and the cathode side catalyst layer 3 includes a supported catalyst 5 b and an ion conductive solid electrolyte 6.

  Next, FIGS. 2A and 2B are schematic cross-sectional views showing examples of the structures of the supported catalyst 5a in the anode side catalyst layer 2 and the supported catalyst 5b in the cathode side catalyst layer 3, respectively. As shown in FIG. 2 (A), the supported catalyst 5a included in the anode side catalyst layer 2 is one in which platinum Pt is supported on the surface of particles of the solid carbon support 7a. Further, as shown in FIG. 2B, the supported catalyst 5b included in the cathode side catalyst layer 3 is one in which platinum Pt is supported on the surface of the particles of the hollow carbon support 7b.

  Since the solid carbon support 7a has a solid shape and the hollow carbon support 7b has a hollow shape, the hollow carbon support 7b is more solid than the solid carbon support 7a at the same particle size. The specific surface area and the amount of platinum Pt supported tend to be large. In addition, the solid carbon support 7a also has a slight internal structure, and the distribution of platinum Pt is that the amount of platinum Pt supported on the outer surface (external surface) is the inner surface (internal (internal)). The amount of platinum Pt supported on the surface) is larger. On the other hand, regarding the distribution of platinum Pt in the hollow carbon carrier 7b, the amount of platinum Pt supported on the inner surface is larger than the amount of platinum Pt supported on the outer surface.

  These supported catalysts 5a and 5b may contain noble metals (including alloys) other than platinum Pt. However, in some cases, particularly in the cathode-side catalyst layer 3, the oxides of the metals are generated. As a result, the catalytic activity of the supported catalyst 5b may be lowered, so that it is preferable that the catalyst substantially contains only platinum.

  In the MEA 1 having such a configuration, a hydrogen gas as a fuel gas is supplied from the anode side catalyst layer 2 and an oxidizing gas such as air is supplied to the cathode side catalyst layer 3 so that the anode side catalyst layer 2 and the cathode side catalyst are supplied. An electromotive force is generated between the layer 3 and a power generation reaction. More specifically, in the anode side catalyst layer 2, hydrogen molecules are oxidized by the catalytic action of platinum to generate protons and electrons. The generated electrons are taken out from the anode side catalyst layer 2 to the external circuit using the carbon carrier as a conductor path, and protons move from the anode side catalyst layer 2 to the cathode side catalyst layer 3 via the electrolyte membrane 4. . Protons that reach the cathode catalyst layer 3 react with the electrons and oxygen molecules supplied from the external circuit using the carbon carrier as a conductor path by the catalytic action of platinum Pt to generate water. Thus, electric energy is generated from the hydrogen gas and the oxygen gas by the MEA 1.

  Here, an example of the electrical characteristics of the supported catalyst 5a in which platinum is supported on the solid carbon support 7a and the supported catalyst 5b in which platinum is supported on the hollow carbon support 7b will be described below. FIG. 3 shows a case where a supported catalyst 5a in which platinum Pt is supported on a solid carbon support 7a is used for the anode side catalyst layer 2 and a supported catalyst 5b in which platinum Pt is supported on a hollow carbon support 7b. It is a graph which shows the change of the electrochemical surface area (ECSA) of platinum Pt with respect to the weight of platinum Pt in the case of being. In addition, the electrochemical surface area (ECSA) of platinum was calculated | required by the cyclic voltammetry (CV) measurement in accordance with the conventional method. The electrochemical surface area (ECSA) indicates the effective area of the supported catalyst that contributes to the reaction on the electrode. The higher this value, the better the dispersibility of platinum in the electrolyte, and the more effective the surface of the supported catalyst. It is an index indicating that it is used for

In FIG. 3, the horizontal axis represents the platinum Pt basis weight [mg / cm ² ], and the vertical axis represents ECSA [m ² / g]. Further, in the same figure, the square mark symbol indicates the data of the supported catalyst 5a in which platinum is supported on the solid carbon support 7a, and the diamond mark symbol indicates the support in which platinum is supported on the hollow carbon support 7b. The data of catalyst 5b are shown. From these results, it is understood that in both the supported catalyst 5a using the solid carbon support 7a and the supported catalyst 5b using the hollow carbon support 7b, the ECSA changes at a substantially constant rate according to the platinum Pt weight. Is done.

Further, when the platinum Pt basis weight was the same, it was found that the supported catalyst 5a using the solid carbon support 7a tended to have a significantly larger ECSA than the supported catalyst 5b using the hollow carbon support 7b. . Thus, for example, as shown by a broken line in FIG. 3, the supported catalyst 5a using the solid carbon support 7a having a platinum Pt basis weight of 0.027 [mg / cm ² ] also has an ECSA of about 23 [m ² / g]. It is understood that this power generation efficiency corresponds to the power generation efficiency of the supported catalyst 5b using the hollow carbon support 7b having a platinum Pt basis weight of 0.038 [mg / cm ² ]. That is, by using the supported catalyst 5a using the solid carbon support 7a for the anode side catalyst layer 2, the utilization efficiency of platinum Pt is enhanced, and as a result, the amount of platinum Pt used is reduced and the cost is reduced. Can do.

FIG. 4 shows a case where a supported catalyst 5a in which platinum Pt is supported on a solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and a supported catalyst in which platinum Pt is supported on a hollow carbon support 7b. It is a graph which shows the change of the cell voltage with respect to the current density in the case of using 5b. In FIG. 4, the horizontal axis represents current density [A / cm ² ], and the vertical axis represents cell voltage [V]. In addition, in the same figure, the symbol of the square mark indicates the data of the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a with the basis weight of 0.027 [mg / cm ² ], and the symbol of the triangular mark is Data of the supported catalyst 5b in which platinum Pt is supported on the hollow carbon support 7b with a basis weight of 0.050 [mg / cm ² ] is shown. Further, in the figure, two broken lines indicate 0.66 [V] @ 2.2 [A / cm ² ], which is the target value (target output) of the current-voltage characteristic.

From these results, the supported catalyst 5a using the solid carbon support 7a and the support using the hollow carbon support 7b at 2.2 [A / cm ² ] which is the current density at the target value of the current-voltage characteristics. The cell voltages of the catalyst 5b are 0.674 [V] and 0.671 [V], respectively, and it is confirmed that both generate voltages near the target cell voltage 0.66 [V] at the target current density. It was. From this, the supported catalyst 5a using the solid carbon support 7a has a basis weight of platinum Pt that is about half that of the platinum Pt of the supported catalyst 5b using the hollow carbon support 7b. It has been found that the current-voltage characteristics are equivalent to those of the supported catalyst 5b using the hollow carbon support 7b.

FIG. 5 shows a case where a supported catalyst 5a in which platinum Pt is supported on a solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and a supported catalyst in which platinum Pt is supported on a hollow carbon support 7b. It is a graph which shows the change of the cell voltage in the target current density with respect to the electrochemical surface area (ECSA) of platinum Pt in the case of using 5b. In FIG. 5, the horizontal axis represents ECSA [m ² / g], and the vertical axis represents the cell voltage [V] at the target current density. FIG. 6 shows the case where the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a is used for both catalyst layers 2 and 3 of the MEA 1, and the platinum Pt is supported on the hollow carbon support 7b. It is a graph which shows the change of the anode overvoltage with respect to the electrochemical surface area (ECSA) of platinum Pt at the time of using the supported catalyst 5b. In FIG. 6, the horizontal axis represents ECSA [m ² / g], and the vertical axis represents anode overvoltage [mV].

5 and 6, the triangular mark symbol indicates data of the supported catalyst 5 a in which platinum Pt is supported on the solid carbon support 7 a with a basis weight of 0.020 [mg / cm ² ]. The symbol indicates data of the supported catalyst 5a in which platinum Pt is supported on a solid carbon support 7a with a basis weight of 0.030 [mg / cm ² ], and the diamond mark symbol indicates that platinum Pt is applied to the hollow carbon support 7b. The data of the supported catalyst 5b supported with a basis weight of 0.050 [mg / cm ² ] are shown. Furthermore, each black symbol indicates initial data when the time-dependent power generation operation is started, and each white symbol is a symbol after performing a power generation operation over time under a predetermined operation condition (that is, after so-called endurance). ) Data. From these results, it is confirmed that both the supported catalyst 5a using the solid carbon support 7a and the supported catalyst 5b using the hollow carbon support 7b have excellent durability during the power generation operation period. It was done.

  According to the fuel cell according to one aspect of the present invention including the MEA 1 configured as described above, since the potential is relatively low on the anode side of the MEA 1, platinum supported on the outer surface of the carbon support in the anode side catalyst layer 2. Even if Pt is in contact with the ionomer 8 (see FIG. 2A), it tends not to be poisoned. Therefore, even if the solid carbon carrier 7a is used as the catalyst carrier of the anode side catalyst layer 2, platinum Pt is not easily poisoned by the ionomer 8, thereby preventing the power generation efficiency from being lowered. In addition, when the solid carbon carrier 7a is used, platinum Pt hardly enters the inside of the carrier, and platinum Pt can be supported on the outer surface that greatly contributes to power generation efficiency. Can reduce the cost.

  Further, since the potential on the cathode side of MEA 1 is relatively high, platinum Pt supported on the outer surface of the carbon support in cathode side catalyst layer 3 is likely to be poisoned when it contacts ionomer 8 (see FIG. 2B). There is a tendency. On the other hand, when the hollow carbon carrier 7b is used as the catalyst carrier of the cathode side catalyst layer 3, platinum Pt also enters and is supported in the hollow portion (inside) of the hollow carbon carrier 7b (FIG. 2B). Compared to the case where the solid carbon support 7a is used, the poisoning of platinum Pt by the ionomer 8 can be reduced, and thereby the reduction in power generation efficiency can be suppressed.

  As described above, according to the present invention, the anode side catalyst layer 2 includes the supported catalyst 5a in which platinum Pt is supported on the solid carbon support 7a, and the cathode side catalyst layer 3 includes platinum Pt on the hollow carbon support 7b. By including the supported catalyst 5b that is supported, the amount of platinum Pt used can be reduced and the cost can be reduced, and the decrease in power generation efficiency due to poisoning of platinum Pt by ionomer can be suppressed. Become.

  Note that, as described above, each of the above embodiments is an example for explaining the present invention, and is not intended to limit the present invention to the embodiment. The present invention can be variously modified without departing from the gist thereof. For example, in the MEA 1, the same type of ion conductive solid electrolyte 6 may be used for the anode side catalyst layer 2, the cathode side catalyst layer 3, and the electrolyte membrane 4, or different types of ion conductive solid electrolytes 6 may be used. May be used.

  According to the fuel cell of the present invention, the amount of platinum used can be reduced to reduce the cost, and the decrease in power generation efficiency due to platinum poisoning by ionomer can be suppressed. The invention is not limited to a power supply device mounted on various moving bodies such as vehicles, ships, airplanes, and portable devices, and a power generation system mounted on a self-propelled device such as a robot, as well as commercial and household using a fuel cell for stationary use It can also be widely used for facilities such as cogeneration systems.

  DESCRIPTION OF SYMBOLS 1 ... MEA, 2 ... Anode side catalyst layer, 3 ... Cathode side catalyst layer, 4 ... Electrolyte membrane, 5a, 5b ... Supported catalyst, 6 ... Ion conductive solid electrolyte, 7a ... Solid carbon support, 7b ... Hollow carbon Carrier, 8 ... Ionoma, Pt ... Platinum.

Claims (1)

A fuel cell comprising an electrolyte membrane, an anode provided on one side of the electrolyte membrane, and a membrane-electrode assembly having a cathode provided on the other side of the electrolyte membrane,
The anode includes a supported catalyst in which platinum is supported on a solid carbon support and has an anode-side catalyst layer disposed opposite to the electrolyte membrane;
The cathode includes a supported catalyst in which platinum is supported on a hollow carbon support and has a cathode-side catalyst layer disposed opposite to the electrolyte membrane;
Fuel cell.

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