Patent Description:
Conventionally, polymer electrolyte fuel cells include a stack in which cells are stacked (see, for example, Patent Literature <NUM>). Each cell includes a power generation portion and two metal separators. The power generation portion includes a membrane electrode assembly and is held between the separators. The separators each include projections and recesses that are alternately formed.

The projections and the recesses define a gas passage between each separator and the power generation portion of the cell such that reactant gas flows through the gas passages. In Patent Literature <NUM>, there is taught a corrugated type separator for a fuel cell stack, with ribs or fins in the gas channels, and parallel ribs in each channel. It is further taught that the height of the ribs may increase in the gas flow direction, out of thermal considerations.

In the fuel cell, power is generated when reactant gas in the gas passage reaches the power generation portion. Thus, it is preferred that the flow rate of reactant gas be high in the vicinity of the power generation portion in the gas passage. Accordingly, it is desired that the flow speed of reactant gas be increased in the vicinity of the power generation portion in the gas passage.

However, the flow speed of reactant gas in the gas passages is lower in a region in the vicinity of the power generation portion than in a middle region of each projection in its protruding direction. Thus, there is room for improvement to increase the power generating performance of the fuel cell.

It is an objective of the present disclosure to provide a separator for a fuel cell capable of increasing the flow speed of reactant gas in the vicinity of a power generation portion.

A separator for a fuel cell that achieves the above-described objective is configured to contact a power generation portion of the fuel cell. The separator includes protrusions that extend in parallel and are spaced apart from each other. The protrusions are configured to contact the power generation portion. The separator includes a gas passage that extends between two adjacent ones of the protrusions along the protrusions. The gas passage is configured to allow reactant gas to flow through the gas passage. A downstream side in a flow direction of the reactant gas flowing through the gas passage is referred to as a downstream side. The gas passage includes at least one rib that protrudes toward the power generation portion and extends in an extending direction of the gas passage. A downstream end of the rib includes a gradually-changing portion that gradually becomes farther from the power generation portion toward the downstream side. The at least one rib include ribs that are arranged in parallel and spaced apart from each other in an arrangement direction of the protrusions.

In this structure, a portion of the gas passage where the rib is disposed has a smaller cross-sectional flow area than other portions of the gas passage. Since the gradually-changing portion of the rib is inclined so as to become farther from the power generation portion toward the downstream side, the cross-sectional flow area of a portion of the gas passage where the gradually-changing portion is disposed gradually increases toward the downstream side. Such an increase in the cross-sectional flow area gradually occurs from the power generation portion.

Accordingly, reactant gas flows faster when passing through the portion of the gas passage where the rib is disposed. The reactant gas flowing faster flows toward the side on which the cross-sectional flow area increases, that is, toward the power generation portion when passing through the gradually-changing portion of the rib. This increases the flow speed of the reactant gas in the vicinity of the power generation portion. Furthermore, the distance between two adjacent ones of the ribs is adjusted so as to limit an increase in the pressure drop of reactant gas, caused by the arrangement of the ribs, and increase the flow speed of reactant gas in the vicinity of the power generation portion.

In the separator for the fuel cell, it is preferred that the ribs include two adjacent ribs in the arrangement direction and that the gradually-changing portions of the two adjacent ribs be located at the same position in the extending direction.

In this structure, the gradually-changing portions allow the reactant gas passing through the space between two adjacent ones of the ribs to easily flow toward the power generation portion and easily flow toward the opposite sides in the arrangement direction of the protrusions. This increases the flow speed of the reactant gas in the vicinity of the power generation portion in a broader range.

In the separator for the fuel cell, it is preferred that a protruding end surface of the rib and a top surface of each of the protrusions be coplanar.

In this structure, the protruding end surfaces of the ribs are in contact with the power generation portion together with the top surfaces of the protrusions. Thus, as compared with when the ribs are not in contact with the power generation portion, the rate of change in the cross-sectional flow area increases between the portion of the gas passage where the ribs are disposed and the portion of the gas passage where the ribs are not disposed. As a result, the pressure difference in reactant gas increases between these portions. Thus, reactant gas flows toward the power generation portion more easily. This further increases the flow speed of the reactant gas in the vicinity of the power generation portion.

In the separator for the fuel cell, it is preferred that an entirety of a protruding end surface of the rib be located between a top surface of each of the protrusions and a bottom of the gas passage in a protruding direction of the protrusions.

In this structure, the ribs are not in contact with the power generation portion. This prevents the power generation portion from being closed by the ribs. Accordingly, a decrease in the power generating performance of the fuel cell is limited.

In the separator for the fuel cell, it is preferred that a widened portion be located downstream of the gradually-changing portion and adjacent to the gradually-changing portion, the widened portion having a larger cross-sectional flow area than a portion of the gas passage where the gradually-changing portion is disposed.

In this structure, a region of the gas passage having a larger cross-sectional flow area than the portion where the gradually-changing portions are disposed (i.e., a region of the gas passage having a smaller pressure drop in reactant gas than that portion) is located downstream of the gradually-changing portions and adjacent to the gradually-changing portions. This ensures that the above-described first operational advantage of the separator for the fuel cell is provided.

The present disclosure increases the flow speed of the reactant gas in the vicinity of the power generation portion.

A separator for a fuel cell according to 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 the components may be different from actual ones.

As shown in <FIG>, a separator for a fuel cell of the present embodiment (hereinafter referred to as the separator <NUM>) is used for a stack <NUM> of a polymer electrolyte fuel cell. The separator <NUM> is a collective term for a first separator <NUM> and a second separator <NUM>, which will be described later.

The stack <NUM> includes a structure in which cells <NUM> are stacked. Each cell <NUM> includes the first separator <NUM> on an anode side, the second separator <NUM> on a cathode side, and a power generation portion <NUM> held between the first separator <NUM> and the second separator <NUM>.

The power generation portion <NUM> includes a membrane electrode assembly <NUM>, an anode-side gas diffusion layer <NUM>, and a cathode-side gas diffusion layer <NUM>. The membrane electrode assembly <NUM> is held between the anode-side gas diffusion layer <NUM> and the cathode-side gas diffusion layer <NUM>. The anode-side gas diffusion layer <NUM> is located between the membrane electrode assembly <NUM> and the first separator <NUM>. The cathode-side gas diffusion layer <NUM> is located between the membrane electrode assembly <NUM> and the second separator <NUM>. The anode-side gas diffusion layer <NUM> and the cathode-side gas diffusion layer <NUM> are made of carbon fibers.

The membrane electrode assembly <NUM> includes an electrolyte membrane <NUM> and two catalytic electrode layers <NUM>. The electrolyte membrane <NUM> is made of a solid polymer material that has an excellent proton conductivity in a wet state. The electrolyte membrane <NUM> is held between the catalytic electrode layers <NUM>. Each catalytic electrode layer <NUM> supports a catalyst (e.g., platinum) in order to expedite the electrochemical reaction of reactant gas in the fuel cell.

The first separator <NUM> is formed by, for example, pressing a composite material that includes a carbon material (e.g., graphite) and a resin material (e.g., polypropylene) serving as binder while heating the composite material. The first separator <NUM> includes protrusions <NUM> and gas passages <NUM>. The protrusions <NUM> extend in parallel and are spaced apart from each other. The protrusions <NUM> are configured to contact the power generation portion <NUM>. Each gas passage <NUM> is arranged between two adjacent ones of the protrusions <NUM>. The gas passage <NUM> is configured to allow reactant gas to flow through the gas passage <NUM>. Each protrusion <NUM> is in contact with the anode-side gas diffusion layer <NUM>. The protrusions <NUM> and the gas passages <NUM> extend in the direction that is orthogonal to the sheet of <FIG>.

The second separator <NUM> is formed by, for example, pressing a composite material that includes a carbon material (e.g., graphite) and a resin material (e.g., polypropylene) while heating the composite material. The second separator <NUM> includes protrusions <NUM> and gas passages <NUM>. The protrusions <NUM> extend in parallel and are spaced apart from each other. The protrusions <NUM> are configured to contact the power generation portion <NUM>. Each gas passage <NUM> is arranged between two adjacent ones of the protrusions <NUM>. The gas passage <NUM> is configured to allow reactant gas to flow through the gas passage <NUM>. Each protrusion <NUM> is in contact with the cathode-side gas diffusion layer <NUM>. The protrusions <NUM> and the gas passages <NUM> extend in the direction that is orthogonal to the sheet of <FIG>.

The section of the first separator <NUM> defined by each gas passage <NUM> and the anode-side gas diffusion layer <NUM> includes a fuel gas passage through which fuel gas (reactant gas) flows. The section of the second separator <NUM> defined by each gas passage <NUM> and the cathode-side gas diffusion layer <NUM> includes an oxidizing gas passage through which oxidizing gas (reactant gas) flows. In the present embodiment, the fuel gas passing through the fuel gas passage is hydrogen, and the oxidizing gas flowing through the oxidizing gas passage is air.

The rear surface of the bottom of each gas passage <NUM> of the first separator <NUM> and the rear surface of the bottom of the gas passage <NUM> of the second separator <NUM> adjacent to the first separator <NUM> are joined to each other through, for example, laser welding. The section defined by the rear surface of the protrusion <NUM> of the first separator <NUM> and the rear surface of the protrusion <NUM> of the second separator <NUM> includes a coolant passage through which coolant flows.

As shown in <FIG>, in the present embodiment, each gas passage <NUM> of the first separator <NUM> includes plate-shaped ribs <NUM>. Although not shown in the drawings, each gas passage <NUM> of the second separator <NUM> includes plate-shaped ribs <NUM>. Since the first separator <NUM> and the second separator <NUM> have the same structure in the present embodiment, the ribs <NUM> of the first separator <NUM> will be hereinafter described and the ribs <NUM> of the second separator <NUM> will not be described.

The arrangement direction of the protrusions <NUM> is hereinafter simply referred to as the arrangement direction. The extending direction of the gas passages <NUM> is hereinafter simply referred to as the extending direction. In the present embodiment, the arrangement direction is orthogonal to the extending direction. The upstream side in the flow direction of reactant gas flowing through the gas passages <NUM> is simply referred to as the upstream side. The downstream side in the flow direction is simply referred to as the downstream side.

As shown in <FIG> and <FIG>, the ribs <NUM> protrude from the bottom of the gas passage <NUM> toward the power generation portion <NUM> and extend in the extending direction. Each rib <NUM> includes an extension <NUM> and a gradually-changing portion <NUM>. The extension <NUM> extends in contact with the power generation portion <NUM>. The gradually-changing portion <NUM> is continuous with the downstream end of the extension <NUM> and located at the downstream end of the rib <NUM>.

As shown in <FIG>, a protruding end surface 51a of each extension <NUM> and a top surface 31a of the corresponding protrusion <NUM> are coplanar. That is, the entire extension <NUM> is in contact with the power generation portion <NUM> in the extending direction. More specifically, the entire extension <NUM> of the rib <NUM> of the first separator <NUM> is in contact with the anode-side gas diffusion layer <NUM> in the extending direction. The entire extension <NUM> of the rib <NUM> of the second separator <NUM> is in contact with the cathode-side gas diffusion layer <NUM> in the extending direction.

The gradually-changing portion <NUM> is inclined so as to gradually become farther from the power generation portion <NUM> toward the downstream side. In other words, the gradually-changing portion <NUM> is inclined such that the protrusion amount from the bottom of the gas passage <NUM> decreases toward the downstream side. The gradually-changing portion <NUM> of the present embodiment is triangular as viewed in the arrangement direction.

The inclination angle of the gradually-changing portion <NUM> relative to the bottom of the gas passage <NUM> is preferably, for example, between <NUM>° and <NUM>°. The inclination angle of the gradually-changing portion <NUM> in the present embodiment is <NUM>°.

As shown in <FIG>, each gas passage <NUM> of the present embodiment includes a pair of ribs <NUM> that are arranged in parallel and spaced apart from each other in the arrangement direction. The ribs <NUM> are located at positions separated from the adjacent protrusions <NUM> in the arrangement direction. That is, a gap is formed between each rib <NUM> and the protrusion <NUM> adjacent to the rib <NUM>. Although not shown in the drawings, the gas passage <NUM> includes pairs of ribs <NUM> that are spaced apart from each other in the extending direction.

Two adjacent ones of the gradually-changing portions <NUM> are located at the same position in the extending direction. In the present embodiment, the ribs <NUM> have the same shape. Thus, two adjacent ones of the gradually-changing portions <NUM> are entirely located at the same position in the extending direction.

A widened portion 32a is located downstream of the gradually-changing portions <NUM> and adjacent to the gradually-changing portions <NUM>. The widened portion 32a has a larger cross-sectional flow area than a portion of the gas passage <NUM> where the gradually-changing portions <NUM> are disposed. The widened portion 32a of the present embodiment is a portion of the gas passage <NUM> where the ribs <NUM> are not disposed.

The operation of the present embodiment will now be described.

The portion of each gas passage <NUM> where the ribs <NUM> are disposed has a smaller cross-sectional flow area than other portions of the gas passage <NUM>. Since the gradually-changing portion <NUM> of each rib <NUM> is inclined so as to gradually become farther from the power generation portion <NUM> toward the downstream side, the cross-sectional flow area of a portion of the gas passage <NUM> where the gradually-changing portion <NUM> is disposed gradually increases toward the downstream side. Such an increase in the cross-sectional flow area gradually occurs from the power generation portion <NUM>.

Accordingly, reactant gas flows faster when passing through the portion of the gas passage <NUM> where the ribs <NUM> are disposed (i.e., through the space between a pair of ribs <NUM> and the space between each rib <NUM> and the corresponding protrusion <NUM>). The reactant gas flowing faster flows toward the side on which the cross-sectional flow area increases (i.e., toward the power generation portion <NUM>) when passing through the gradually-changing portions <NUM> of the ribs <NUM>.

As shown by the arrow in <FIG>, the flow of the reactant gas toward the power generation portion <NUM> flows in an orientation that is generally orthogonal to the oblique side of the gradually-changing portion <NUM>. Thus, the reactant gas reaches the power generation portion <NUM> on the upstream side more easily when the inclination angle of the gradually-changing portion <NUM> is <NUM>° than when, for example, the inclination angle of the gradually-changing portion <NUM> is <NUM>°.

The advantages of the present embodiment will now be described.

In this structure, a region of the gas passage <NUM> having a larger cross-sectional flow area than the portion where the gradually-changing portions <NUM> are disposed (i.e., a region of the gas passage <NUM> having a smaller pressure drop in reactant gas than that portion) is located downstream of the gradually-changing portions <NUM> and adjacent to the gradually-changing portions <NUM>. This ensures that the above-described advantage (<NUM>) is provided.

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.

In the following first to fourth modifications respectively shown in <FIG>, the same components as those in the above-described embodiment are given the same reference numbers. Also, the components that correspond to those in the above-described embodiments are given reference numbers obtained by adding <NUM>, <NUM>, <NUM>, and <NUM> to the reference numbers of the components of the above-described embodiments, and will not be described.

As shown in <FIG>, the widened portion 32a may be replaced with two pairs of ribs <NUM> adjacent to each other in the extending direction. In this modification, the gradually-changing portions <NUM> of the upstream ribs <NUM> and the extensions <NUM> of the downstream ribs <NUM> are continuous with each other in the extending direction.

As shown in <FIG>, the entirety of a protruding end surface 251a of an extension <NUM> may be located between the top surface 31a of each protrusion <NUM> and the bottom of the gas passage <NUM> in the protruding direction (upward direction in <FIG>) of the protrusion <NUM>. That is, a gap G may be formed between the ribs <NUM> and the power generation portion <NUM> over the entire gas passage <NUM> in the extending direction. In such a structure, the ribs <NUM> are not in contact with the power generation portion <NUM>. This prevents the power generation portion <NUM> from being closed by the ribs <NUM>. Accordingly, a decrease in the power generating performance of the fuel cell is limited.

Only part of each rib <NUM> in the extending direction may be in contact with the power generation portion <NUM>.

The gradually-changing portions <NUM> of two adjacent ones of the ribs <NUM> may each be located at a different position in the extending direction. As shown in <FIG>, this structure may include ribs <NUM> and ribs <NUM> each having an extension <NUM> that is shorter than the extension <NUM> of the corresponding rib <NUM> in the extending direction. Further, the upstream edges of the extensions <NUM>, <NUM> may be located at the same position in the extending direction.

Each gas passage <NUM> may include a single rib <NUM>. Even in this case, the cross-sectional flow area is reduced between the rib <NUM> and the protrusion <NUM> adjacent to the rib <NUM> and thus the above-described advantage (<NUM>) is provided.

Each gas passage <NUM> may include three or more ribs <NUM> that are arranged in parallel and spaced apart from each other in the arrangement direction.

As shown in <FIG>, ribs <NUM> may each include a gradually-changing portion <NUM> at the upstream end in addition to a gradually-changing portion <NUM> at the downstream end. The gradually-changing portion <NUM> is inclined so as to gradually become farther from the power generation portion <NUM> toward the upstream side. That is, the gradually-changing portion <NUM> is inclined such that the protrusion amount from the bottom of the gas passage <NUM> decreases toward the upstream side. In this modification, two pairs of ribs <NUM> are adjacent to each other in the extending direction. That is, the gradually-changing portion <NUM> of each upstream rib <NUM> is continuous with the gradually-changing portion <NUM> of the corresponding downstream rib <NUM> in the extending direction. In this structure, when reactant gas that has passed through the space between the gradually-changing portions <NUM> of the upstream ribs <NUM> flows toward the power generation portion <NUM>, some of the reactant gas flows along the gradually-changing portions <NUM> of the downstream ribs <NUM>. Thus, the reactant gas easily flows toward the power generation portion <NUM>.

The inclination angle of the gradually-changing portion <NUM> relative to the bottom of the gas passage <NUM> may be changed.

The gradually-changing portion <NUM> may include steps so as to be step-shaped shape as viewed in the arrangement direction. Even in this case, the gradually-changing portion <NUM> gradually becomes farther from the power generation portion <NUM> toward the downstream side. Thus, the above-described advantage (<NUM>) is provided.

In the present embodiment, the first separator <NUM> and the second separator <NUM> both include the ribs <NUM>. Instead, only the first separator <NUM> may include the ribs <NUM>. Alternatively, only the second separator <NUM> may include the ribs <NUM>.

Claim 1:
A separator (<NUM>, <NUM>, <NUM>) for a fuel cell, the separator being configured to contact a power generation portion (<NUM>) of the fuel cell, the separator comprising:
protrusions (<NUM>, <NUM>) that extend in parallel and are spaced apart from each other, the protrusions being configured to contact the power generation portion; and
a gas passage (<NUM>, <NUM>) that extends between two adjacent ones of the protrusions along the protrusions, the gas passage being configured to allow reactant gas to flow through the gas passage, wherein
a downstream side in a flow direction of the reactant gas flowing through the gas passage is referred to as a downstream side,
the gas passage includes at least one rib (<NUM>) that protrudes toward the power generation portion and extends in an extending direction of the gas passage,
a downstream end of the rib includes a gradually-changing portion (<NUM>) that gradually becomes farther from the power generation portion toward the downstream side, and
the at least one rib includes ribs (<NUM>) that are arranged in parallel and spaced apart from each other in an arrangement direction of the protrusions.