JPH0544781B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention relates to a fuel cell in which a porous electrode base material is disposed in contact with an electrode layer that performs power generation in a fuel cell to which a reactive fluid containing non-reactive components is supplied. The reaction fluid is passed through a plurality of reaction fluid passages arranged on the opposite side of the electrode base material from the electrode layer, and the fuel is diffused within the electrode base material and supplies the reaction fluid to the electrode layer. The present invention relates to a battery, and particularly to a structure for supplying a reactive fluid to an electrode layer thereof.

[Prior art and its problems]

Generally, in a fuel cell, a porous electrode base material having a passage for a reaction fluid is arranged between a fuel electrode and an oxidizer electrode that sandwich an electrolyte layer, and the reaction fluid is supplied to the electrode by diffusing into the electrode base material from the passage. For example, in a phosphoric acid fuel cell, a gas is used as the reaction fluid, a reformed gas containing hydrogen as the main component is used as the fuel gas, and air is used as the oxidant gas. is supplied to the unit cell to cause an electrochemical reaction to occur, but the hydrogen and oxygen in the reaction gas are consumed as the reaction gas flows from the inlet to the outlet of the passage. Component concentration gradually decreases. The prior art will be explained below based on the drawings.

FIG. 1 is an exploded perspective view showing the structure of a conventional fuel cell, in which an electrolyte 1 is sandwiched, a fuel electrode 2 and an oxidizer electrode 3 are arranged on both sides, and a fuel electrode 2 is placed on the outside. An electrode base material 4 in which a groove 4a for supplying fuel gas is formed as a passage on the opposite side of the contacting surface is closely attached to the fuel electrode 2, and a supply groove 4a is formed on the opposite side of the surface contacting the oxidizer electrode 3.
An electrode base material 5 in which a groove 5a for supplying oxidant gas is formed as a passage in a direction perpendicular to the direction of A large number of separate plates 6 are interposed, and a large number of these plates are stacked to form a cell stack.

A manifold 7 having an inlet pipe 7a for supplying fuel gas is provided on one side of the cell stack, and a manifold 7 having an outlet pipe for discharging fuel gas (not shown) is provided on the opposite side. A manifold 8 having an inlet pipe 8a for supplying oxidizing gas is provided on the side of the cell stack perpendicular to the surface for supplying and discharging fuel gas, and a manifold 8 having an outlet pipe for discharging oxidizing gas (not shown) is opposite to the above. A fuel cell is constructed by being provided on the side of the cell stack.

In operation of the fuel cell, fuel gas as a reaction gas is introduced from the inlet pipe 7a, flows through the manifold 7 into the fuel gas supply groove 4a of the cell stack, is diffused into the porous electrode base material 4, and is supplied to the fuel electrode 2. The fuel gas is collected in a discharge manifold (not shown) and discharged from an outlet pipe. On the other hand, the oxidant gas is similarly passed through the inlet pipe 8a and the supply manifold 8 into the oxidant gas supply groove 5a, diffused into the porous electrode base material 5, and supplied to the oxidant electrode 3. The oxidant gas is collected in a discharge manifold (not shown) and discharged from an outlet pipe, and these reaction gases undergo an electrochemical reaction within the unit cell to generate electricity.

FIG. 2 is a cross-sectional view showing the situation in which the above-mentioned reaction gas diffuses within the porous electrode base material, and the fuel gas flows in the direction of arrow A through the supply groove 4a of the electrode base material 4.
The oxidant gas is diffused in the direction of arrow B in the electrode base material 4 and supplied to the fuel electrode 2, and the oxidizing gas is supplied to the electrode base material 5.
The oxidizing agent flows through the supply groove 5a in a direction perpendicular to the plane of the paper and diffuses in the electrode base material 5 in the direction of arrow C.
The electrolyte of matrix 1 and oxygen and hydrogen in the reaction gas undergo an electrochemical reaction at the electrode. Therefore, the concentrations of oxygen in the air and hydrogen in the reformed gas gradually decrease from the inlet of the supply groove, which serves as a reaction gas passage, toward the outlet pipe.

Therefore, as shown in FIG.
In the conventional method using a porous electrode base material in which the cross-sectional area of the passage consisting of the reactive gas supply structure 4a is equal from the inlet to the outlet, the reactive gas flows through the electrode base material from the reactive gas supply groove. Since the average diffusion resistance of two-dimensional diffusion is constant along the path, the amount of oxygen and hydrogen in the reaction gas supplied to each electrode is directly affected by the concentration of oxygen and hydrogen components in the reaction gas flowing through the supply groove. Ru.

Therefore, on the electrode surface, a non-uniform current distribution occurs, in which the generated current is large at the inlet of the reactant gas, and conversely, the generated current is small at the outlet side. In addition, changes in battery characteristics over time depend on current density, and the higher the current density, the higher the temperature due to the temperature rise accompanying the increase in heat generation density, and the greater the deterioration of characteristics over time. Therefore, when a fuel cell with uneven current distribution is operated for a long period of time, the parts with high current density initially deteriorate first, and as a result, the current density in adjacent parts compensates for the current in the deteriorated parts. The cost increases, and the areas of deterioration gradually expand.

In this way, in the conventional structure having reaction gas supply grooves, the average diffusion resistance for reaction gas to diffuse within the electrode base material is constant along the path consisting of the reaction gas supply grooves, so the reaction supplied to the electrode The gas amount is affected by the concentration of the reactant gas components, and there is a drawback that non-uniform current distribution is inevitable, which adversely affects the life of the battery.

[Purpose of the invention]

In view of the above-mentioned drawbacks, the present invention provides a structure for supplying a reactive fluid to an electrode layer of a fuel cell, by diffusing an electrode base material from a passage of the reactive fluid and making the amount of components of the reactive fluid supplied to the electrode almost uniform on the surface of the electrode layer. The purpose is to provide.

[Summary of the invention]

In order to achieve the above object, according to the present invention,
Two electrode layers, a fuel electrode layer and an oxidant electrode layer, are arranged with an electrolyte layer in between, and a porous electrode base material is arranged in contact with each of the two electrode layers. A plurality of reaction fluid passages through which a reaction fluid containing non-reactive components flows are arranged on the opposite side of the electrode base material from the electrode layer, and are laminated with plates in between, and the reaction fluid passages are arranged on the side opposite to the electrode layer of the electrode substrate, and the reaction fluid passages are connected to the electrode. In a fuel cell in which grooves are formed in parallel in the base material itself or in parallel grooves in the gas non-diffusive plate, the reactant fluid flows from the surface of the electrode base material facing each of the reactant fluid passages. The average diffusion resistance value of the two-dimensional diffusion path that diffuses inside the electrode base material and reaches the electrode layer and the concentration of the reaction component in the reaction fluid flowing through the reaction fluid path are determined from the entrance of the path. This is achieved by sequentially branching the reaction fluid passages from the inlet to the outlet so that the number of grooves increases sequentially so that the relationship is substantially proportional throughout the outlet.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings. FIG. 4 is a perspective view of an electrode base material of a unit battery using a ribbed electrode method according to an embodiment of the present invention, and FIGS. 5 and 6 are YY cross-sectional views and XX cross-sectional views in FIG. 4, respectively. It is a diagram. In the figures from FIG. 4 onward, the same parts as in FIGS. 1, 2, and 3 are given the same reference numerals.

In FIG. 4, fuel gas as a reaction gas flows in the direction of the arrow in the supply groove 4a as a reaction fluid passage of the porous electrode base material 4, but the number of supply grooves 4a is in the direction of the arrow, i.e. The number of branch supply grooves increases in the direction in which the fuel gas flows from the inlet to the outlet. Therefore, as the number of branch supply grooves increases, the distance between adjacent supply grooves becomes shorter, and the length of the diffusion path that diffuses the electrode base material from the supply groove to reach the electrode also becomes shorter. In addition, in FIG. 4, the flow path of the reaction fluid sequentially branches toward the reaction fluid outlet, and the reaction fluid path gradually increases, so that the flow rate of the reaction fluid decreases, but as the reaction fluid path expands, the reaction There is no reduction in the concentration of reactants in the fluid. Therefore, the average diffusion resistance value of the two-dimensional diffusion path and the concentration of the reaction component in the reaction fluid have a substantially proportional relationship.

FIG. 5 shows Y where fuel gas is supplied to the fuel electrode 2 by diffusing inside the porous electrode base material 4 from the supply groove 4a.
The state in the -Y cross section is shown, and the fuel is supplied to the fuel electrode 2 after being two-dimensionally diffused in the direction of arrow D from the inner and bottom surfaces of the supply groove 4a.

FIG. 6 shows that the fuel gas is flowing from the inner surface and bottom of the supply groove 4a in the XX cross section in FIG. The state in which the fuel is two-dimensionally diffused in the direction of and supplied to the fuel electrode 2 is shown. Here, since the number of supply grooves in the XX cross section of FIG. 6 is greater than the number of supply grooves in the YY cross section of FIG. The path length of the path, that is, the average diffusion resistance value becomes smaller in the direction of arrow D. That is, by increasing the number of branch supply grooves in the supply groove, the average diffusion resistance value becomes smaller. Furthermore, the same effect can be obtained by using the same structure as described above for the electrode base material for oxidant gas.

Therefore, when a reactant gas is supplied to the unit cell by operating a fuel cell having the above structure, a reaction occurs in the reactant gas due to an electrochemical reaction that occurs when the flow passes through the electrode base material from the inlet to the outlet. The amount of components, such as hydrogen and oxygen, is consumed by the reaction, and the concentration of the reacting components decreases from the inlet to the outlet. Correspondingly, the average diffusion resistance value is not directly proportional to the component concentration, but gradually decreases. Since it decreases almost proportionally, the reaction components in the reaction gas are supplied to the electrode surface in an approximately equal amount, and the current distribution on the electrode surface during operation becomes approximately equal.

FIG. 7 shows a different embodiment of the present invention, in which a ribbed separator type unit battery is shown.
FIG. 2 is a cross-sectional view of a porous electrode base material interposed between an electrode and a ribbed separator. In FIG. 7, grooves 10a for supplying fuel gas as a reaction gas are provided on the lower surface of the ribbed separator 10 in a direction perpendicular to the plane of the paper, while grooves 10a are provided on the upper surface for supplying fuel gas as a reaction gas in a direction perpendicular to the supply grooves 10a. A gas-inhibitory ribbed separator consisting of grooves 10b provided in the fuel electrode 2 is provided, and a porous electrode base material 14 is interposed between the supply groove 10a and the fuel electrode 2, and although not shown, the fuel electrode is in contact with electrolyte. Further, the supply groove 10b of the ribbed separator 10 is also in contact with a porous electrode base material interposed between the oxidizing agent electrode and the ribbed separator 10 (not shown).

In this example, when the fuel gas flows through the supply groove 10a, the fuel gas diffuses in the porous electrode base material 14 in the direction of arrow F and is supplied to the fuel electrode 2. Therefore, if the supply grooves of the ribbed separator are equivalent to the reaction fluid passages having the branched supply grooves provided in the electrode base material 4 of the ribbed electrode method as shown in FIG. A structure that decreases from the inlet to the outlet of the reaction fluid passageway of the substrate is obtained, and the same effect as described above is obtained.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the diffusion resistance value in the diffusion path where the reaction fluid containing non-reactive components diffuses from the reaction fluid path through the porous electrode base material and reaches the electrode layer is By providing a supply structure in which the concentration of the reaction component in the reaction fluid decreases in proportion to the decrease in concentration of the reaction component in the reaction fluid, which decreases as the fluid is consumed by electrochemical reaction from the inlet to the outlet of the reaction fluid passage of the electrode base material. Since the reaction components of the reaction fluid are supplied in almost equal amounts to the entire electrochemical reaction surface of the electrode layer, an even current distribution can be obtained on the electrode layer surface, which has the effect of extending the life of the fuel cell. .

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing the configuration of a conventional fuel cell, and FIG. 2 is a partial cross-sectional explanatory view showing the situation in which the reaction fluid diffuses into the ribbed electrode base material in FIG. 1.
FIG. 3 is a partial perspective view showing the ribbed electrode base material in FIG. 1, FIG. 4 is a partial perspective view showing the ribbed electrode base material according to the embodiment of the present invention, and FIGS. FIG. 4 is an explanatory cross-sectional view showing the situation in which the reaction fluid diffuses in the YY cross section and the X-X cross section in FIG. 4, and FIG. 7 is a cross-sectional explanatory view showing the situation in which the reaction fluid diffuses according to another different embodiment. 2: Fuel electrode, 3: Oxidizer electrode, 4, 5: Ribbed electrode base material, 4a, 5a: Reaction fluid supply path, 1
0: Separator with ribs, 10a, 10b: Reaction fluid supply path, 14: Electrode base material.

Claims (1)

[Claims] 1. A structure in which two electrode layers, a fuel electrode layer and an oxidizer electrode layer, are arranged with an electrolyte layer in between, and a porous electrode base material is arranged in contact with each of the two electrode layers is considered to be gas non-diffusible. A plurality of reaction fluid passages through which a reaction fluid containing non-reactive components flows are provided on the opposite side of the electrode layer from the electrode layer of the electrode base material, and the reaction fluid passages In a fuel cell in which grooves are formed in parallel on the electrode base material itself or grooves are formed in parallel on the gas-nondiffusive plate, the reaction fluid flows from the surface of the electrode base material facing each of the reaction fluid passages. The average diffusion resistance value of the two-dimensional diffusion path during which the reaction fluid diffuses inside the electrode base material and reaches the electrode layer, and the concentration of the reaction component in the reaction fluid flowing through the reaction fluid path are determined at the entrance of the passage. A fuel cell characterized in that the reactant fluid passage is sequentially branched from the inlet to the outlet so that the number of channels is increased sequentially so that a substantially proportional relationship is established from the inlet to the outlet.