Patent Description:
Polymer electrolyte fuel cells include a fuel cell stack that includes stacked cells (see, for example, Patent Document <NUM>). Each cell disclosed in Patent Document <NUM> includes a power generation portion including a membrane electrode assembly, two separators that hold the power generation portion, and a gas passage defining plate disposed between the power generation portion and the two separators.

The gas passage defining plate includes recesses and projections that are alternately arranged. The gas passage defining plate also includes a gas passage portion including a mesh-shaped part defined by the recesses and the projections and by the power generation portion. Reactant gas, such as fuel gas or oxidant gas, flows through the gas passage portion.

Each cell has a rectangular shape in plan view. A fuel gas supply port through which fuel gas is supplied and a fuel gas discharge port through which fuel gas is discharged are respectively disposed at the opposite ends of the power generation portion on the short sides of the cell. Oxidant gas supply ports through which oxidant gas is supplied and oxidant gas discharge ports through which oxidant gas is discharged are respectively disposed at the opposite ends of the power generation portion on the long sides of the cell. The oxidant gas supply ports are spaced apart from each other in the longitudinal direction of the long sides of the cell. Likewise, the oxidant gas discharge ports are spaced apart from each other in the longitudinal direction of the long sides of the cell.

The oxidant gas supplied from the oxidant gas supply ports is supplied to the power generation portion through the gas passage portion of the gas passage defining plate. In the power generation portion, the oxidant gas electrochemically reacts with the fuel gas so as to generate power. The oxidant gas that has not been used to generate power in the power generation portion is discharged out of the oxidant gas discharge ports through the gas passage portion.

In the fuel cell stack, in order to improve the power-generating efficiency, it is preferred that reactant gas be diffused over a wider range of the power generation portion (i.e., over a wider range of the gas passage portion).

However, since the oxidant gas supply ports are spaced apart from each other in the longitudinal direction of the long sides of the cell, a partition is disposed between adjacent ones of the oxidant gas supply ports to divide the oxidant gas supply ports from each other. Thus, the oxidant gas flowing from the oxidant gas supply ports through the gas passage portion toward the oxidant gas discharge ports does not easily flow to a portion adjacent to each partition. Accordingly, there is room for improvement to allow reactant gas to be diffused over a wider range of the gas passage portion (i.e., to improve the performance of distributing reactant gas).

It is an objective of present disclosure to provide a fuel cell stack capable of improving the performance of distributing reactant gas.

A fuel cell stack that achieves the above-described objective includes stacked cells. Each cell includes a sheet-shaped power generation portion, two separators that hold the power generation portion in a thickness direction, a gas passage defining plate disposed between at least one of the two separators and the power generation portion, the gas passage defining plate including a gas passage portion through which reactant gas flows, and a frame member disposed around the gas passage defining plate, the frame member including a supply port through which the reactant gas is supplied to the gas passage portion and a discharge port through which the reactant gas is discharged from the gas passage portion. A flow direction of the reactant gas flowing from the supply port toward the discharge port is referred to as a flow direction. A direction in which the power generation portion opposes the gas passage portion is referred to as an opposing direction. A direction that is orthogonal to the flow direction and the opposing direction is referred to as an orthogonal direction. The gas passage portion includes opposing portions extended in the flow direction and arranged in parallel in the orthogonal direction, the opposing portions opposing the power generation portion. A main passage is defined between each of the opposing portions and the power generation portion. The gas passage portion includes connection passages each connecting the main passages to each other and being spaced apart from each other in the flow direction. The gas passage portion includes a first passage portion and a second passage portion, the first passage portion being adjacent to the supply port in the flow direction, and the second passage portion being adjacent to the first passage portion in the orthogonal direction. The main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.

In this structure, the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion. Thus, the reactant gas in the main passages of the second passage portion causes a smaller pressure drop than the reactant gas in the main passages of the first passage portion. Accordingly, the reactant gas that has flowed from each of the supply ports to the main passages of the first passage portion easily flows to the main passages of the second passage portion through the connection passages. That is, the reactant gas that has flowed from each of the supply ports easily flows from the first passage portion toward the second passage portion. This allows the reactant gas to be distributed over a wider range of the gas passage portion. Accordingly, the performance of distributing reactant gas improves.

In the fuel cell stack, it is preferred that the opposing portions of the second passage portion be farther from the power generation portion in the opposing direction than the opposing portions of the first passage portion.

In this structure, the opposing portions defining the main passages of the second passage portion are farther from the power generation portion in the opposing direction than the opposing portions defining the main passages of the first passage portion. Thus, the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.

Thus, in this structure, a simple change is made so as to change the distances of the opposing portions from the power generation portion. As a result, the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.

In the fuel cell stack, it is preferred that the opposing portions of the second passage portion each have a larger width in the orthogonal direction than the opposing portions of the first passage portion.

In this structure, the width of each of the opposing portions defining the main passages of the second passage portion is larger than the width of the corresponding one of the opposing portions defining the main passages of the first passage portion. Thus, the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.

Thus, in this structure, a simple change is made so as to change the width of each opposing portion in the orthogonal direction, As a result, the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.

In the fuel cell stack, it is preferred that the gas passage portion include a third passage portion that is adjacent to the first passage portion on a downstream side in the flow direction and that the main passages of the second third passage portion each have a smaller cross-sectional flow area than the main passages of the first passage portion.

In this structure, the main passages of the third passage portion each have a smaller cross-sectional flow area than the main passages of the first passage portion. Thus, the reactant gas in the main passages of the third passage portion causes a larger pressure drop than the reactant gas in the main passages of the first passage portion. As a result, the reactant gas that has flowed from each of the supply ports to the main passages of the first passage portion flows to the second passage portion, which have a relatively small pressure drop, more easily than to the third passage portion, which have a relatively large pressure drop. Accordingly, the performance of distributing reactant gas further improves.

In the fuel cell stack, it is preferred that the opposing portions of the third passage portion be closer to the power generation portion in the opposing direction than the opposing portions of the first passage portion.

In this structure, the opposing portions defining the main passages of the third passage portion are closer to the power generation portion in the opposing direction than the opposing portions defining the main passages of the first passage portion. Thus, the main passages of the third passage portion each have a smaller cross-sectional flow area than the main passages of the first passage portion.

Thus, in this structure, a simple change is made so as to change the distances of the opposing portions from the power generation portion. As a result, the main passages of the third passage portion each have a smaller cross-sectional flow area than the main passages of the first passage portion.

In the fuel cell stack, it is preferred that each of the opposing portions of the first passage portion be made continuous with a corresponding one of the opposing portions of the third passage portion by a step.

This structure causes the reactant gas flowing in the flow direction to collide with the steps. Thus, the pressure drop of reactant gas easily increases at the boundary between the first passage portion and the third passage portion. This increases the difference in pressure drop of reactant gas between the first passage portion and the third passage portion.

In the fuel cell stack, it is preferred that the gas passage portion include wavy portions that are integrally disposed on opposite sides of each of the opposing portions in the orthogonal direction, the wavy portions each having a wavy cross-sectional shape that is orthogonal to the orthogonal direction. It is preferred that each of the wavy portions include first projections and second projections, the first projections protruding closer to the power generation portion than the opposing portions and being in contact with the power generation portion, the second projections protruding closer to a corresponding one of the separators than the opposing portions and being in contact with the separators, and the first projections and the second projections being alternately arranged in the flow direction. It is preferred that each of the connection passages be defined by the first projections and the opposing portions. It is preferred that the connection passages of the second passage portion each have a larger cross-sectional flow area than the connection passages of the first passage portion.

In this structure, the connection passages of the second passage portion each have a larger cross-sectional flow area than the connection passages of the first passage portion. Thus, the reactant gas in the connection passages of the second passage portion causes a smaller pressure drop than the reactant gas in the connection passages of the first passage portion. Accordingly, the reactant gas that has flowed from each of the supply ports to the first passage portion easily flows to the second passage portion through the connection passages of the second passage portion. That is, the reactant gas that has flowed from each of the supply ports easily flows from the first passage portion toward the second passage portion. Accordingly, the performance of distributing reactant gas further improves.

In the fuel cell stack, it is preferred that the gas passage portion include a third passage portion that is adjacent to the first passage portion on a downstream side in the flow direction and the connection passages of the third passage portion each have a smaller cross-sectional flow area than the connection passages of the first passage portion.

In this structure, the connection passages of the third passage portion each have a smaller cross-sectional flow area than the connection passages of the first passage portion. Thus, the reactant gas in the connection passages of the third passage portion causes a larger pressure drop than the reactant gas in the connection passages of the first passage portion. Accordingly, the reactant gas that has flowed from each of the supply ports to the first passage portion flows to the second passage portion through the connection passages of the second passage portion more easily than to the connection passages of the third passage portion. Accordingly, the performance of distributing reactant gas further improves.

The fuel cell stack according to the present disclosure improves the performance of distributing reactant gas.

An embodiment will now be described with reference to <FIG>.

For illustrative purposes, some parts of the structures in the drawings may be exaggerated or simplified. Further, the dimensional ratios of portions may be different among the drawings.

Referring to <FIG>, the fuel cell stack according to the present embodiment is a polymer electrolyte fuel cell including stacked cells <NUM> that each have a substantially rectangular shape in plan view. Each cell <NUM> includes a membrane electrode gas diffusion layer assembly <NUM> (hereinafter referred to as MEGA <NUM>), a first separator <NUM>, and a second separator <NUM>. The MEGA <NUM> includes a sheet-shaped power generation portion <NUM>. The first separator <NUM> and the second separator <NUM> hold the MEGA <NUM> in the thickness direction. A gas passage defining plate <NUM> is disposed between the MEGA <NUM> and the second separator <NUM>. The gas passage defining plate <NUM> includes a gas passage portion <NUM> through which reactant gas flows.

The first separator <NUM> is located on the anode side of the power generation portion <NUM>. The second separator <NUM> is located on the cathode side of the power generation portion <NUM>.

As shown in <FIG>, a frame member <NUM> is disposed around the gas passage defining plate <NUM>. The frame member <NUM> is made of plastic and has the shape of a substantially rectangular plate in plan view. The MEGA <NUM> and the gas passage defining plate <NUM> that are overlapped with each other are fitted to the frame member <NUM> of the present embodiment. The frame member <NUM> is held by the first separator <NUM> and the second separator <NUM> in the thickness direction.

In the description of <FIG>, the up-down direction and the left-right direction of <FIG> are hereinafter simply referred to as the up-down direction and the left-right direction, respectively. The up-down direction and the left-right direction do not indicate an actual position of the frame member <NUM>.

The frame member <NUM> includes a fuel gas supply port <NUM> through which fuel gas is supplied as reactant gas and a fuel gas discharge port <NUM> through which fuel gas is discharged. The fuel gas supply port <NUM> and the fuel gas discharge port <NUM> are respectively located on the opposite sides of the gas passage defining plate <NUM> in the left-right direction. The fuel gas in the present embodiment is, for example, hydrogen gas. The fuel gas supply port <NUM> is located on the left of the gas passage defining plate <NUM> at a position closer to the upper side of the gas passage defining plate <NUM> than the middle of the gas passage defining plate <NUM> in the up-down direction. The fuel gas discharge port <NUM> is located on the right of the gas passage defining plate <NUM> at a position closer to the lower side of the gas passage defining plate <NUM> than the middle of the gas passage defining plate <NUM> in the up-down direction.

Three coolant supply ports <NUM> are disposed on the lower side of the fuel gas supply port <NUM> and spaced apart from each other in the up-down direction. Coolant is supplied through the three coolant supply ports <NUM> toward the power generation portion <NUM>. Three coolant discharge ports <NUM> are disposed on the upper side of the fuel gas discharge port <NUM> and spaced apart from each other in the up-down direction. Coolant is discharged through the three coolant discharge ports <NUM> from the power generation portion <NUM>.

The frame member <NUM> further includes oxidant gas supply ports <NUM> through which oxidant gas is supplied as reactant gas and oxidant gas discharge ports <NUM> through which oxidant gas is discharged. The oxidant gas supply ports <NUM> and the oxidant gas discharge ports <NUM> are respectively located on the opposite ends of the gas passage defining plate <NUM> in the up-down direction. The oxidant gas in the present embodiment is, for example, air. In the present embodiment, six oxidant gas supply ports <NUM> are spaced apart from each other in the left-right direction. Likewise, six oxidant gas discharge ports <NUM> are spaced apart from each other in the left-right direction. A partition <NUM> is disposed between adjacent ones of the oxidant gas supply ports <NUM> to divide the oxidant gas supply ports <NUM> from each other.

The first separator <NUM> and the second separator <NUM> include through-holes (not shown) at positions corresponding to the supply ports <NUM>, <NUM>, <NUM> and the discharge ports <NUM>, <NUM>, <NUM>.

The oxidant gas supplied from the oxidant gas supply ports <NUM> flows to the gas passage defining plate <NUM> and is then discharged out of the oxidant gas discharge ports <NUM>.

The direction in which oxidant gas flows from the oxidant gas supply ports <NUM> toward the oxidant gas discharge ports <NUM> is hereinafter referred to as the flow direction X. The direction in which the power generation portion <NUM> opposes the gas passage portion <NUM> of the gas passage defining plate <NUM> is hereinafter referred to as the opposing direction Y. The direction that is orthogonal to the flow direction X and the opposing direction Y is hereinafter referred to as the orthogonal direction Z.

The components of the cell <NUM> will now be described in detail.

As shown in <FIG>, the MEGA <NUM> includes a membrane electrode assembly <NUM>, an anode-side gas diffusion layer <NUM>, and a cathode-side gas diffusion layer <NUM>. The anode-side gas diffusion layer <NUM> and the cathode-side gas diffusion layer <NUM>, which are formed using carbon fibers, hold the membrane electrode assembly <NUM>. The membrane electrode assembly <NUM> includes an electrolyte membrane <NUM> and two catalytic electrode layers <NUM> that hold the electrolyte membrane <NUM>. The electrolyte membrane <NUM> is made of a solid polymer material that has an excellent proton conductivity in a wet state. Each catalytic electrode layer <NUM> supports a catalyst, such as platinum, in order to expedite the electrochemical reaction of reactant gas in the fuel cell.

Referring to <FIG>, the first separator <NUM> is formed by pressing a metal (e.g., stainless steel) plate. The middle portion of the first separator <NUM> is in contact with the anode-side gas diffusion layer <NUM> of the MEGA <NUM>. Although not shown in the drawings, the portion located outward from the middle portion of the first separator <NUM> is in contact with the frame member <NUM>.

The middle portion of the first separator <NUM> defines fuel gas passages <NUM> that extend at least in the flow direction X and have the shape of a groove. The fuel gas passages <NUM> are connected to the fuel gas supply port <NUM> and the fuel gas discharge port <NUM>.

The surface of the first separator <NUM> on the side opposite from the fuel gas passages <NUM> defines coolant passages <NUM> that have the shape of a groove. The coolant passages <NUM> are each located between adjacent ones of the fuel gas passages <NUM> and connected to the coolant supply ports <NUM> and the coolant discharge ports <NUM>.

Referring to <FIG>, the second separator <NUM> of each cell <NUM> is formed by pressing a metal (e.g., stainless steel) plate. The second separator <NUM> includes a first surface and a second surface in the opposing direction Y. The first surface is in contact with the gas passage defining plate <NUM>. The second surface is in contact with the first separator <NUM> of the adjacent cell <NUM>.

Referring to <FIG>, the gas passage defining plate <NUM> is formed by rolling a metal (e.g., stainless steel) plate.

As shown in <FIG>, the gas passage portion <NUM> includes regions that differ from each other in shape. More specifically, the gas passage portion <NUM> includes a first passage portion <NUM> adjacent to the oxidant gas supply ports <NUM> in the flow direction X, a second passage portion <NUM> adjacent to the first passage portion <NUM> in the orthogonal direction Z, and a third passage portion <NUM> adjacent to the first passage portion <NUM> on the downstream side in the flow direction X. Further, the gas passage portion <NUM> has different shapes in the first to third passage portions <NUM> to <NUM>.

The length of the first passage portion <NUM> in the orthogonal direction Z is substantially equal to the length of each oxidant gas supply port <NUM> in the orthogonal direction Z. The length of the second passage portion <NUM> in the orthogonal direction Z is substantially equal to the length of each partition <NUM> in the orthogonal direction Z. The length of the third passage portion <NUM> in the orthogonal direction Z is substantially equal to the length of the first passage portion <NUM> in the orthogonal direction Z. The length of the first passage portion <NUM> in the flow direction X is substantially equal to the length of the second passage portion <NUM> in the flow direction X.

The shapes of the first passage portion <NUM>, the second passage portion <NUM>, and the third passage portion <NUM> will now be described.

As shown in <FIG>, <FIG>, the first passage portion <NUM> includes opposing portions <NUM> that oppose the power generation portion <NUM>. The opposing portions <NUM> extend in the flow direction X and are arranged in parallel in the orthogonal direction Z. Each opposing portion <NUM> has the shape of a substantially quadrilateral bar. <FIG> is a perspective view showing the first passage portion <NUM> having the basic shape of the gas passage portion <NUM>.

Wavy portions <NUM>, <NUM> are integrally disposed on the opposite sides of each opposing portion <NUM> in the orthogonal direction Z. The wavy portions <NUM>, <NUM> each have a wavy cross-sectional shape that is orthogonal to the orthogonal direction Z.

The wavy portions <NUM>, <NUM> have the same shape. Thus, only the structure of the wavy portion <NUM> will be hereinafter described. The components of the wavy portion <NUM> are given reference number <NUM>*, which is obtained by adding <NUM> to reference number <NUM>* of the wavy portion <NUM>, and redundant description will not be made.

Each wavy portion <NUM> includes first projections <NUM> and second projections <NUM>. Each first projection <NUM> protrudes closer to the power generation portion <NUM> than the opposing portion <NUM> and is in contact with the power generation portion <NUM> (more specifically, in contact with the cathode-side gas diffusion layer <NUM>). Each second projection <NUM> protrudes closer to the second separator <NUM> than the opposing portion <NUM> and is in contact with the second separator <NUM>. Each of the first projections <NUM> and the second projections <NUM> includes a flat top extending in the flow direction X. The first projections <NUM> and the second projections <NUM> are alternately arranged in the flow direction X. Each first projection <NUM> includes two inclined portions <NUM> on the opposite sides of the first projection <NUM> in the flow direction X. Each inclined portion <NUM> is inclined with respect to the opposing direction Y and coupled to the corresponding second projection <NUM>.

The wavy portions <NUM> and the wavy portions <NUM> are disposed adjacent to each other in the orthogonal direction Z such that the first projections <NUM> are adjacent to second projections <NUM> in the orthogonal direction Z and the second projections <NUM> are adjacent to first projections <NUM> in the orthogonal direction Z.

As shown in <FIG>, a main passage <NUM> is defined between each opposing portion <NUM> and the power generation portion <NUM>. The oxidant gas supplied from the oxidant gas supply ports <NUM> flows through the main passages <NUM>. The main passages <NUM> are defined in correspondence with the opposing portions <NUM> and thus arranged in parallel in the orthogonal direction Z.

The cross-sectional flow area of each main passage <NUM> hereinafter refers to the cross-sectional flow area of each main passage <NUM> on a plane that is orthogonal to the flow direction X.

A water passage <NUM> is defined between each opposing portion <NUM> and the second separator <NUM>. Generated water that is generated through the electrochemical reaction in the power generation portion <NUM> flows through the water passages <NUM>.

As shown in <FIG>, the first passage portion <NUM> includes connection passages <NUM> that each connect the main passages <NUM> to each other. The connection passages <NUM> are spaced apart from each other in the flow direction X. The connection passages <NUM> are defined by the first projections <NUM>, <NUM> of the wavy portions <NUM>, <NUM> and by the opposing portions <NUM> on a plane that is orthogonal to the orthogonal direction Z.

A sub-passage <NUM> is defined between two of the connection passages <NUM> adjacent to each other in the flow direction X. Each sub-passage <NUM> connects these two connection passages <NUM> to each other. The sub-passages <NUM> are defined by the first projections <NUM> and the first projections <NUM> (more specifically, by inclined portions <NUM> and inclined portions <NUM>) of the wavy portion <NUM> and the wavy portion <NUM> adjacent to each other and by the power generation portion <NUM> on the plane that is orthogonal to the orthogonal direction Z.

The cross-sectional flow area of each connection passage <NUM> hereinafter refers to the cross-sectional flow area of each connection passage <NUM> on the plane that is orthogonal to the orthogonal direction Z. The cross-sectional flow area of each sub-passage <NUM> hereinafter refers to the cross-sectional flow area of each sub-passage <NUM> on the plane that is orthogonal to the orthogonal direction Z.

Each wavy portion <NUM> and the corresponding wavy portion <NUM> are disposed such that the connection passages <NUM> each have a larger cross-sectional flow area than the sub-passages <NUM>. Thus, the oxidant gas flowing through the connection passages <NUM> causes a smaller pressure drop than the oxidant gas flowing through the sub-passages <NUM>. Accordingly, most of the oxidant gas flowing through each main passage <NUM> flows to the adjacent main passage <NUM> through the corresponding connection passage <NUM>.

The shape of the second passage portion <NUM> is similar to that of the first passage portion <NUM>. The components of the second passage portion <NUM> are hereinafter given reference number <NUM>**, which is obtained by adding <NUM> to reference number <NUM>**, and redundant description may be omitted.

As shown in <FIG> and <FIG>, width W2 of each opposing portion <NUM> of the second passage portion <NUM> in the orthogonal direction Z is larger than width W1 of the corresponding opposing portion <NUM> of the first passage portion <NUM> in the orthogonal direction Z. The opposing portions <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM>. Thus, main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

As shown in <FIG> and <FIG>, length L2 of the tops of first projections <NUM> and first projections <NUM> of the second passage portion <NUM> in the flow direction X is longer than length L1 of the tops of first projections <NUM> and first projections <NUM> of the first passage portion <NUM> in the flow direction X. Thus, connection passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>.

Inclined portions <NUM>, <NUM> of the second passage portion <NUM> have the same shape as the inclined portions <NUM>, <NUM> of the first passage portion <NUM>. Thus, sub-passages <NUM> of the second passage portion <NUM> each have the same cross-sectional flow area as the sub-passages <NUM> of the first passage portion <NUM>.

The shape of the third passage portion <NUM> is similar to that of the first passage portion <NUM>. The components of the second passage portion <NUM> are hereinafter given reference number <NUM>**, which is obtained by adding <NUM> to reference number <NUM>**, and redundant description may be omitted.

As shown in <FIG> and <FIG>, width W3 of each opposing portion <NUM> of the third passage portion <NUM> in the orthogonal direction Z is equal to width W1 of the corresponding opposing portion <NUM> of the first passage portion <NUM> in the orthogonal direction Z. The opposing portions <NUM> are closer to the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM>. Thus, main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

As shown in <FIG> and <FIG>, length L3 of the tops of first projections <NUM> and first projections <NUM> of the third passage portion <NUM> in the flow direction X is shorter than length L1 of the tops of first projections <NUM> and first projections <NUM> of the first passage portion <NUM> in the flow direction X. Thus, connection passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>.

Inclined portions <NUM>,<NUM> of the third passage portion <NUM> have the same shape as the inclined portions <NUM>, <NUM> of the first passage portion <NUM>. Thus, sub-passages <NUM> of the third passage portion <NUM> each have the same cross-sectional flow area as the sub-passages <NUM> of the first passage portion <NUM>.

As shown in <FIG>, the opposing portion <NUM> and the opposing portion <NUM> that extend in the flow direction X have a different distance from the power generation portion <NUM>. This creates a step <NUM> at the boundary between the opposing portions <NUM> and <NUM>.

The operation of the present embodiment will now be described.

The main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>. Thus, the oxidant gas in the main passages <NUM> of the second passage portion <NUM> causes a smaller pressure drop than the oxidant gas in the main passages <NUM> of the first passage portion <NUM>. Accordingly, as shown by arrow A in <FIG>, the oxidant gas that has flowed from the oxidant gas supply port <NUM> to the main passages <NUM> of the first passage portion <NUM> easily flows to the main passages <NUM> of the second passage portion <NUM> through the connection passages <NUM> (operation <NUM>).

Further, the main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>. Thus, the oxidant gas in the main passages <NUM> of the third passage portion <NUM> causes a larger pressure drop than the oxidant gas in the main passages <NUM> of the first passage portion <NUM>. Accordingly, as shown by arrow A in <FIG>, the oxidant gas flowing from the oxidant gas supply port <NUM> to the main passages <NUM> of the first passage portion <NUM> flows to the second passage portion <NUM>, which have a relatively small pressure drop, more easily than through the third passage portion <NUM>, which have a relatively large pressure drop (operation <NUM>).

Further, the connection passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>. Thus, the oxidant gas in the connection passages <NUM> of the second passage portion <NUM> causes a smaller pressure drop than the oxidant gas in the connection passages <NUM> of the first passage portion <NUM>. Accordingly, as shown by arrow A in <FIG>, the oxidant gas that has flowed from each of the oxidant gas supply ports <NUM> to the first passage portion <NUM> easily flows to the second passage portion <NUM> through the connection passages <NUM> of the second passage portion <NUM>. That is, the oxidant gas that has flowed from each of the oxidant gas supply ports <NUM> easily flows from the first passage portion <NUM> toward the second passage portion <NUM> (operation <NUM>).

The connection passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>. Thus, the oxidant gas in the connection passages <NUM> of the third passage portion <NUM> causes a larger pressure drop than the oxidant gas in the connection passages <NUM> of the first passage portion <NUM>. Accordingly, as shown by arrow A in <FIG>, the oxidant gas that has flowed from each of the oxidant gas supply ports <NUM> to the first passage portion <NUM> flows to the second passage portion <NUM> through the connection passages <NUM> of the second passage portion <NUM> more easily than through the connection passages <NUM> of the third passage portion <NUM> (operation <NUM>).

The advantages of the embodiment will now be described.

Such a structure produces the above-described operation <NUM>. Thus, the oxidant gas that has flowed from the oxidant gas supply ports <NUM> easily flows from the first passage portion <NUM> toward the second passage portion <NUM>. This allows the oxidant gas to be distributed over a wider range of the gas passage portion <NUM>. Accordingly, the performance of distributing oxidant gas improves.

(<NUM>) The opposing portions <NUM> of the second passage portion <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>.

In such a structure, the opposing portions <NUM> defining the main passages <NUM> of the second passage portion <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> defining the main passages <NUM> of the first passage portion <NUM>. Thus, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

In this structure, a simple change is made so as to change the distances of the opposing portions <NUM> from the power generation portion <NUM>. As a result, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

(<NUM>) Width W2 of each opposing portion <NUM> of the second passage portion <NUM> in the orthogonal direction Z is larger than width W1 of the corresponding opposing portion <NUM> of the first passage portion <NUM> in the orthogonal direction Z.

In such a structure, width W2 of each of the opposing portions <NUM> defining the main passages <NUM> of the second passage portion <NUM> is larger than width W1 of the corresponding one of the opposing portions <NUM> defining the main passages <NUM> of the first passage portion <NUM>. Thus, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

In this structure, a simple change is made so as to change width W2 of each opposing portion <NUM> in the orthogonal direction Z. As a result, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

(<NUM>) The main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

Such a structure produces the above-described operation <NUM> and thus further improves the performance of distributing oxidant gas.

(<NUM>) The opposing portions <NUM> of the third passage portion <NUM> are closer to the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>.

In such a structure, the opposing portions <NUM> defining the main passages <NUM> of the third passage portion <NUM> are closer to the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> defining the main passages <NUM> of the first passage portion <NUM>. Thus, the main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

In this structure, a simple change is made so as to change the distances of the opposing portions <NUM> from the power generation portion <NUM>. As a result, the main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>.

(<NUM>) The opposing portions <NUM> of the first passage portion <NUM> are respectively made continuous with the opposing portions <NUM> of the third passage portion <NUM> by the steps <NUM>.

Such a structure causes the reactant gas flowing in the flow direction X to collide with the steps <NUM>. Thus, the pressure drop of oxidant gas easily increases at the boundary between the first passage portion <NUM> and the third passage portion <NUM>. This increases the difference in pressure drop of oxidant gas between the first passage portion <NUM> and the third passage portion <NUM>.

(<NUM>) The connection passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>.

(<NUM>) The connection passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>.

The present embodiment may be modified as follows. The present embodiment and the following modifications can be combined as long as they remain technically consistent with each other.

As shown in <FIG>, the third passage portion <NUM> may be adjacent to the first passage portion <NUM> and the second passage portion <NUM> on the downstream side in the flow direction X. This limits the flow of oxidant gas from the second passage portion <NUM> toward the third passage portion <NUM> and thus allows the oxidant gas to easily flow in the orthogonal direction Z.

As shown in <FIG>, the gas passage portion <NUM> may include second passage portions <NUM> that are adjacent to the opposite sides of each first passage portion <NUM> in the orthogonal direction Z.

In the present embodiment, the sub-passages <NUM> of the first passage portion <NUM> each have the same cross-sectional flow area as the sub-passages <NUM> of the second passage portion <NUM>. Instead, as shown in <FIG>, the sub-passages <NUM> may each have a larger cross-sectional flow area than the sub-passages <NUM>. In this case, the oxidant gas in the sub-passages <NUM> of the second passage portion <NUM> causes a smaller pressure drop than the oxidant gas in the sub-passages <NUM> of the first passage portion <NUM>. Accordingly, the oxidant gas flowing from the oxidant gas supply ports <NUM> to the first passage portion <NUM> easily flows to the second passage portion <NUM> through the sub-passages <NUM> of the second passage portion <NUM>. That is, the oxidant gas that has flowed from each of the oxidant gas supply ports <NUM> easily flows from the first passage portion <NUM> toward the second passage portion <NUM>. This allows the oxidant gas to be distributed over a wider range of the gas passage portion <NUM>. In this modification, the inclination angles of the inclined portions <NUM>, <NUM> with respect to the opposing direction Y are set to be smaller than the inclination angles of the inclined portions <NUM>, <NUM> with respect to the opposing direction Y so that the sub-passages <NUM> each have a larger cross-sectional flow area than the sub-passages <NUM>.

In the present embodiment, the sub-passages <NUM> of the first passage portion <NUM> each have the same cross-sectional flow area as the sub-passages <NUM> of the third passage portion <NUM>. Instead, as shown in <FIG>, the sub-passages <NUM> may each have a smaller cross-sectional flow area than the sub-passages <NUM>. In this case, the oxidant gas in the sub-passages <NUM> of the third passage portion <NUM> causes a larger pressure drop than the oxidant gas in the sub-passages <NUM> of the first passage portion <NUM>. Accordingly, the oxidant gas flowing from the oxidant gas supply ports <NUM> to the first passage portion <NUM> flows to the second passage portion <NUM> through the sub-passages <NUM> of the second passage portion <NUM> than through the sub-passages <NUM> of the third passage portion <NUM>. That is, the oxidant gas that has flowed from the oxidant gas supply ports <NUM> easily flows from the first passage portion <NUM> toward the second passage portion <NUM>. This allows the oxidant gas to be distributed over a wider range of the gas passage portion <NUM>. In this modification, the inclination angles of the inclined portions <NUM>, <NUM> with respect to the opposing direction Y are set to be larger than the inclination angles of the inclined portions <NUM>, <NUM> with respect to the opposing direction Y so that the sub-passages <NUM> each have a smaller cross-sectional flow area than the sub-passages <NUM>.

Length L1 of the tops of the first projections <NUM>, <NUM> of the first passage portion <NUM> may be equal to length L3 of the tops of the first projections <NUM>, <NUM> of the third passage portion <NUM>. Even in this case, the opposing portions <NUM> of the third passage portion <NUM> are closer to the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>. Thus, the main passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>. This provides the above-described advantage (<NUM>).

Length L1 of the tops of the first projections <NUM>, <NUM> of the first passage portion <NUM> may be equal to length L3 of the tops of the second projections <NUM>, <NUM> of the second passage portion <NUM>. Even in this case, the opposing portions <NUM> of the second passage portion <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>, and width W2 of each opposing portion <NUM> is larger than width W1 of the corresponding opposing portion <NUM>. Thus, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>. This provides the above-described advantages (<NUM>) to (<NUM>).

The inclination angles of the inclined portions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be changed so as to change the cross-sectional flow areas of the connection passages <NUM>, <NUM>, <NUM>.

In the present embodiment, the first passage portion <NUM> includes the wavy portion <NUM> and the wavy portion <NUM> that are disposed between two opposing portions <NUM> arranged in the orthogonal direction Z. Instead, only one wavy portion <NUM> or one wavy portion <NUM> may be disposed between two opposing portions <NUM>. Alternatively, three or more wavy portions <NUM>, <NUM> may be disposed between two opposing portions <NUM>. The second passage portion <NUM> and the third passage portion <NUM> may be changed in the same manner.

The opposing portions <NUM>, <NUM>, <NUM> may be inclined so as to approach the power generation portion <NUM> in the opposing direction Y toward the downstream side in the flow direction X. In this case, the pressure drop of oxidant gas gradually increases toward the downstream side in the flow direction X.

The distance of each opposing portion <NUM> of the third passage portion <NUM> from the power generation portion <NUM> may be equal to the distance of the corresponding opposing portion <NUM> of the first passage portion <NUM> from the power generation portion <NUM>. Even in this case, length L3 of the tops of the first projections <NUM>, <NUM> of the third passage portion <NUM> is shorter than length L1 of the tops of the first projections <NUM>, <NUM> of the first passage portion <NUM>. Thus, the connection passages <NUM> of the third passage portion <NUM> each have a smaller cross-sectional flow area than the connection passages <NUM> of the first passage portion <NUM>. This provides the above-described advantage (<NUM>).

The following structure may be employed. That is, the distance of each opposing portion <NUM> of the third passage portion <NUM> from the power generation portion <NUM> is equal to the distance of the corresponding opposing portion <NUM> of the first passage portion <NUM> from the power generation portion <NUM>, and length L3 of the tops of the first projections <NUM>, <NUM> of the third passage portion <NUM> is equal to length L1 of the tops of the first projections <NUM>, <NUM> of the first passage portion <NUM>. Even in this case, the opposing portions <NUM> of the second passage portion <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>, and width W2 of each opposing portion <NUM> is larger than width W1 of the corresponding opposing portion <NUM>. Further, length L2 of the tops of the first projections <NUM>, <NUM> of the second passage portion <NUM> is longer than length L1 of the tops of the first projections <NUM>, <NUM> of the first passage portion <NUM>. Thus, the main passages <NUM> of the second passage portion <NUM> each have a larger cross-sectional flow area than the main passages <NUM> of the first passage portion <NUM>. This provides the above-described advantages (<NUM>) to (<NUM>).

As long as the opposing portions <NUM> of the second passage portion <NUM> are farther from the power generation portion <NUM> in the opposing direction Y than the opposing portions <NUM> of the first passage portion <NUM>, width W2 of each opposing portion <NUM> may be equal to width W1 of the corresponding opposing portion <NUM>.

As long as width W2 of each opposing portion <NUM> of the second passage portion <NUM> is larger than width W1 of the corresponding opposing portion <NUM> of the first passage portion <NUM>, the distance of the opposing portions <NUM> from the power generation portion <NUM> may be equal to the distance of the opposing portions <NUM> from the power generation portion <NUM>.

In the present embodiment, the gas passage defining plate <NUM> is located on the cathode side, to which oxidant gas is supplied. Instead, the gas passage defining plate <NUM> may be located on the anode side, to which fuel gas is supplied.

In the gas passage portion <NUM>, the portions other than the first passage portion <NUM>, second passage portion <NUM>, and third passage portion <NUM> may be changed in shape. For example, the portions may have the same shape as the first passage portion <NUM>.

Claim 1:
A fuel cell stack, comprising stacked cells each including:
a sheet-shaped power generation portion;
two separators that hold the power generation portion in a thickness direction;
a gas passage defining plate disposed between at least one of the two separators and the power generation portion, the gas passage defining plate including a gas passage portion through which reactant gas flows; and
a frame member disposed around the gas passage defining plate, the frame member including a supply port through which the reactant gas is supplied to the gas passage portion and a discharge port through which the reactant gas is discharged from the gas passage portion, wherein
a flow direction of the reactant gas flowing from the supply port toward the discharge port is referred to as a flow direction,
a direction in which the power generation portion opposes the gas passage portion is referred to as an opposing direction,
a direction that is orthogonal to the flow direction and the opposing direction is referred to as an orthogonal direction,
the gas passage portion includes opposing portions extended in the flow direction and arranged in parallel in the orthogonal direction, the opposing portions opposing the power generation portion,
a main passage is defined between each of the opposing portions and the power generation portion,
the gas passage portion includes connection passages each connecting the main passages to each other and being spaced apart from each other in the flow direction,
the gas passage portion includes a first passage portion and a second passage portion, the first passage portion being adjacent to the supply port in the flow direction, and the second passage portion being adjacent to the first passage portion in the orthogonal direction, and
the main passages of the second passage portion each have a larger cross-sectional flow area than the main passages of the first passage portion.