Fuel battery

Abstract

To provide a fuel battery that can suppress the decline in power generation performance.SOLUTION: A fuel battery includes at least a power generation portion and a pair of separators sandwiching the power generation portion, the pair of separators includes grooves that form flow paths, the power generation portion includes a gas diffusion layer, and in the region of the power generation portion, a surface pressure on the upstream side in the flow direction of an oxidant gas is greater than a surface pressure on the downstream side in the flow direction of the oxidant gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fuel cells. [Background technology]

[0002] Various technologies have been proposed regarding fuel cells, such as those disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-171598 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-147501 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a technique for uniformly distributing the surface pressure of a fuel cell. On the downstream side of the fuel cell in the direction of oxidant gas flow, gas diffusion resistance is more dominant than electrical resistance. Therefore, if the surface pressure of the fuel cell is too high, the gas diffusion resistance increases, potentially resulting in a decrease in the power generation performance of the fuel cell.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a fuel cell that can suppress a decrease in power generation performance. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A fuel cell, the fuel cell has at least a power generation unit and a pair of separators that sandwich the power generation unit; The pair of separators have grooves that form flow paths, the power generation section includes a gas diffusion layer, A fuel cell, wherein in the region of the power generation section, the surface pressure on the upstream side in the flow direction of the oxidizing gas is greater than the surface pressure on the downstream side in the flow direction of the oxidizing gas.

[0007] <2> When the gas diffusion layer is not pressurized, the thickness of the gas diffusion layer on the upstream side in the flow direction of the oxidizing gas is greater than the thickness of the gas diffusion layer on the downstream side in the flow direction of the oxidizing gas. <1> The fuel cell according to claim 1.

[0008] <3> the density of the gas diffusion layer on the upstream side in the flow direction of the oxidant gas is greater than the density of the gas diffusion layer on the downstream side in the flow direction of the oxidant gas; <1> or <2> The fuel cell according to claim 1.

[0009] <4> a depth of the groove on the upstream side in the flow direction of the oxidant gas is greater than a depth of the groove on the downstream side in the flow direction of the oxidant gas. <1> ~ <3> 10. The fuel cell according to claim 9, wherein the fuel cell is a fuel cell having a capacity of 1000 m / s.

[0010] <5> one of the pair of separators is a cathode separator and the other is an anode separator; the cathode separator has the groove that forms an oxidant gas flow path, The upstream side in the flow direction of the oxidant gas is a region of 30% to 70% from the oxidant gas inlet side of the oxidant gas flow channel, when the entire region of the oxidant gas flow channel is taken as 100%. <1> ~ <4> 10. The fuel cell according to claim 9, wherein the fuel cell is a fuel cell having a capacity of 1000 m / s. [Effects of the Invention]

[0011] The fuel cell of the present disclosure can suppress a decrease in power generation performance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. [Figure 2] FIG. 2 is a schematic diagram showing another example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. [Figure 3] FIG. 3 is a schematic diagram showing another example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a fuel cell that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In this disclosure, the gas supplied to the anode of a fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of a fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas that contains mainly hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, etc. In this disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gases or gases.

[0014] The present disclosure provides a fuel cell, comprising: the fuel cell has at least a power generation unit and a pair of separators that sandwich the power generation unit; The pair of separators have grooves that form flow paths, the power generation section includes a gas diffusion layer, The fuel cell has a region of the power generation section in which the surface pressure on the upstream side in the oxidant gas flow direction is greater than the surface pressure on the downstream side in the oxidant gas flow direction.

[0015] This disclosure provides a means for controlling surface pressure distribution to improve the power generation performance of a fuel cell. Conventional techniques improve the power generation performance of a fuel cell by applying as uniform a surface pressure as possible to the power generation section of the cell and reducing the electrical resistance of the fuel cell at a surface pressure above a certain level. However, depending on the part of the power generation section, there are areas where high surface pressure is better and areas where low surface pressure is better, making it difficult to obtain optimal power generation performance. Because gas diffusion resistance dominates over electrical resistance on the downstream side of the cell in the oxidant gas flow direction, high surface pressure causes the gas diffusion layer to collapse, increasing gas diffusion resistance and reducing the power generation performance of the fuel cell. In this disclosure, by setting the surface pressure distribution in the oxidant gas flow direction such that the upstream side is greater than the downstream side, priority is given to reducing electrical resistance on the upstream side of the flow direction and priority is given to reducing gas diffusion resistance on the downstream side of the flow direction, thereby achieving an appropriate power generation state. The surface pressure distribution is controlled by setting the distribution of the thickness of the gas diffusion layer, the density of the gas diffusion layer, or the height of the flow channel as the realization structure.

[0016] In various applications such as vehicles, when operating auxiliary equipment such as air compressors while suppressing the power consumption to an air stoichiometric ratio of, for example, 2 or less, concentration overvoltage is likely to occur due to a drop in oxygen partial pressure in approximately one-third of the downstream side of the oxidant gas flow path in the flow direction. In proton-conductive fuel cells, protons and oxygen meet on the cathode side to generate electricity, so oxygen must migrate to the catalyst surface in the presence of generated moisture. Therefore, the surface pressure design of the present disclosure is suitable for proton-conductive fuel cells, for which gas diffusion on the cathode side is likely to be an issue. In a fuel cell of the type in which products are generated on the anode side and in which a gas diffusion layer that is dependent on surface pressure is used, the surface pressure may be designed to be the same as that on the cathode side based on the flow direction of the anode gas. Regarding the flow channel type, a groove flow channel type is more suitable because the area under the rib is more susceptible to gas diffusion than a porous flow channel in which gas is supplied more uniformly. The groove flow channel type may be a groove flow channel without a restriction or a groove flow channel with a restriction.

[0017] The fuel cell of the present disclosure may be mounted on a moving object such as a vehicle, or may be mounted on a vehicle. The fuel cell of the present disclosure may also be mounted on a stationary power generation system such as a generator. The vehicle may be a fuel cell vehicle, etc. Examples of moving bodies other than vehicles include trains, ships, and aircraft. Furthermore, the fuel cell of the present disclosure may be mounted on a mobile object such as a vehicle that can also run on power from a secondary battery. A mobile object and a stationary power generation system may include the fuel cell of the present disclosure. The mobile object may have a drive unit such as a motor, an inverter, a hybrid control system, and the like. The hybrid control system may be capable of running a mobile object using both the output of the fuel cell and the power of the secondary battery.

[0018] The fuel cell may have only one unit cell (cell), or may be a fuel cell stack (stack) in which a plurality of cells are stacked. In this disclosure, both cells and fuel cell stacks may be referred to as fuel cells. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, from 2 to several hundred.

[0019] A cell of a fuel cell has at least a power generation section and a pair of separators that sandwich the power generation section.

[0020] The power generating section may have a rectangular shape in a plan view. The power generation section has at least a gas diffusion layer. The power generation section may have a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes that sandwich the electrolyte membrane. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, and a hydrocarbon-based electrolyte membrane. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont). The two electrodes are an anode (fuel electrode) and a cathode (oxidant electrode). The electrodes include catalyst layers and may include gas diffusion layers as needed. The power generation section may be a membrane electrode gas diffusion layer assembly (MEGA). In this case, the cell may include a cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer. The anode catalyst layer and the cathode catalyst layer are collectively referred to as catalyst layers. The anode side gas diffusion layer and the cathode side gas diffusion layer are collectively referred to as gas diffusion layers. The catalyst layer includes a catalyst, and the catalyst may include a catalytic metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity. Examples of catalyst metals that can be used include platinum (Pt) and alloys of Pt with other metals (e.g., Pt alloys mixed with cobalt and nickel, etc.) The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different. The electrolyte may be a fluorine-based resin, etc. As the fluorine-based resin, for example, a Nafion solution may be used. The catalytic metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalytic metal (catalyst-supported carrier) and the electrolyte may be mixed together. Examples of the carrier for supporting the catalytic metal include carbon materials such as carbon, which are generally available commercially. The gas diffusion layer (GDL) may be composed of a substrate and a mesoporous layer (MPL). The GDL may have a substrate on the side that contacts the separator and an MPL on the side that contacts the catalyst layer. The substrate may be a gas-permeable conductive member or the like. Examples of the substrate include porous carbon materials such as carbon cloth and carbon paper, and porous metal materials such as metal mesh and foam metal. The MPL may comprise a mixture of a water-repellent resin, such as PTFE, and a conductive material, such as carbon black. MPL may contain an antioxidant such as Ce, which can prevent the generation of radicals. The cell may include an insulating resin frame disposed on the outer periphery (periphery) of the membrane electrode assembly in the planar direction between the anode separator and the cathode separator. The resin frame is molded into a plate-like frame shape using a thermoplastic resin, and seals the gap between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. For example, resins such as PE, PP, PET, and PEN can be used as the resin frame. The resin frame may be a three-layer sheet composed of three layers with adhesive layers disposed on the surface layers.

[0021] The fuel cell stack may have gaskets, resin sheets, etc. between the cells to seal the gases. The resin sheets may be the resin frames described above.

[0022] The separators collect the current generated by power generation and function as partition walls. In the cell, the separators are arranged on both sides of the power generation section in the stacking direction so that the pair of separators sandwich the power generation section. One of the pair of separators is an anode separator, and the other is a cathode separator. The anode separator and the cathode separator are collectively referred to as separators. The pair of separators have grooves that form flow paths. The anode separator may have grooves that form fuel gas flow paths on the surface facing the power generation section. The cathode separator may have grooves that form oxidant gas flow paths on the surface facing the power generation section. The separator may have holes that constitute manifolds such as supply holes and discharge holes for passing fluids such as reaction gases and coolants in the stacking direction of the cells. The refrigerant may be water, a mixed solvent of water and ethylene glycol, or the like. The separator may be made of, for example, dense carbon made by compressing carbon to make it gas impermeable, or a press-molded metal (for example, iron, titanium, stainless steel, etc.).

[0023] In the region of the power generation section of the fuel cell, the surface pressure on the upstream side in the oxidant gas flow direction is greater than the surface pressure on the downstream side in the oxidant gas flow direction.

[0024] From the viewpoint of providing a surface pressure distribution in the region of the power generation unit of the fuel cell, when the gas diffusion layer is not pressurized, the thickness of the gas diffusion layer on the upstream side in the oxidant gas flow direction may be greater than the thickness of the gas diffusion layer on the downstream side in the oxidant gas flow direction. When the gas diffusion layer is not pressurized, the thickness of at least one of the anode-side gas diffusion layer and the cathode-side gas diffusion layer on the upstream side in the oxidant gas flow direction may be greater than the thickness of the gas diffusion layer on the downstream side in the oxidant gas flow direction. When the gas diffusion layer is not pressurized, the thickness of the cathode-side gas diffusion layer on the upstream side in the oxidant gas flow direction may be greater than the thickness of the cathode-side gas diffusion layer on the downstream side in the oxidant gas flow direction. When the gas diffusion layer is not pressurized, the thickness of the anode-side gas diffusion layer on the upstream side in the oxidant gas flow direction may be greater than the thickness of the anode-side gas diffusion layer on the downstream side in the oxidant gas flow direction. When the gas diffusion layer is pressurized, the thickness of the gas diffusion layer on the upstream side in the oxidant gas flow direction may be the same as the thickness of the gas diffusion layer on the downstream side in the oxidant gas flow direction.

[0025] From the viewpoint of providing a surface pressure distribution in the region of the power generation section of the fuel cell, the density of the gas diffusion layer upstream in the oxidant gas flow direction may be greater than the density of the gas diffusion layer downstream in the oxidant gas flow direction. The density of at least one of the anode-side gas diffusion layer and the cathode-side gas diffusion layer upstream in the oxidant gas flow direction may be greater than the density of the gas diffusion layer downstream in the oxidant gas flow direction. The density of the cathode-side gas diffusion layer upstream in the oxidant gas flow direction may be greater than the density of the cathode-side gas diffusion layer downstream in the oxidant gas flow direction. The density of the anode-side gas diffusion layer upstream in the oxidant gas flow direction may be greater than the density of the anode-side gas diffusion layer downstream in the oxidant gas flow direction.

[0026] The material of the gas diffusion layer on the upstream side in the oxidant gas flow direction may be different from or the same as the material of the gas diffusion layer on the downstream side in the oxidant gas flow direction.

[0027] The flow direction of the fuel gas may be the same as the flow direction of the oxidant gas, or may be a counter-flow.

[0028] From the viewpoint of providing a surface pressure distribution in the region of the power generation unit of the fuel cell, the groove depth of the separator on the upstream side in the oxidant gas flow direction may be greater than the groove depth of the separator on the downstream side in the oxidant gas flow direction. The groove depth of at least one of the anode separator and the cathode separator on the upstream side in the oxidant gas flow direction may be greater than the groove depth of the separator on the downstream side in the oxidant gas flow direction. The groove depth of the cathode separator on the upstream side in the oxidant gas flow direction may be greater than the groove depth of the cathode separator on the downstream side in the oxidant gas flow direction. The groove depth of the anode separator on the upstream side in the oxidant gas flow direction may be greater than the groove depth of the anode separator on the downstream side in the oxidant gas flow direction.

[0029] In the present disclosure, the upstream side in the flow direction of the oxidant gas may be a region of 30% to 70%, a region of 50% to 70%, or a region of 70% from the oxidant gas inlet side of the oxidant gas flow channel, when the entire region of the oxidant gas flow channel is taken as 100%. In the present disclosure, the downstream side in the oxidant gas flow direction may be a region that is 30% to 70%, a region that is 30% to 50%, or a region that is 30%, from the oxidant gas outlet side of the oxidant gas flow channel, when the entire region of the oxidant gas flow channel is taken as 100%. The surface pressure distribution may be designed according to the operating conditions of the fuel cell, the specifications of the separator flow passages, the specifications of the MEGA, and the like. For example, the surface pressure in a region of 70% from the oxidant gas inlet side of the oxidant gas flow channel may be higher than the surface pressure in a region of 30% from the oxidant gas outlet side of the oxidant gas flow channel.

[0030] FIG. 1 is a schematic diagram showing an example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. The cathode separator 100 of the fuel cell in FIG. FIG. 2 is a schematic diagram showing another example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. 2 has one oxidant gas flow channel 20. The single oxidant gas flow channel 20 branches into multiple flow channels on the upstream side 40 in the oxidant gas flow direction, and the multiple branched flow channels join together on the downstream side 50 in the oxidant gas flow direction. FIG. 3 is a schematic diagram showing another example of a cathode separator of a fuel cell according to the present disclosure when viewed from above. The cathode separator 300 of the fuel cell of FIG. 1 to 3, when the supply rate of oxidant gas F is optimized in consideration of fuel efficiency, the concentration overvoltage becomes large in a range of approximately the downstream 30% of the oxidant gas flow channel. Therefore, the surface pressure in a region 70% from the oxidant gas inlet side of the oxidant gas flow channel, which is the upstream side 40 in the oxidant gas flow direction, is higher than the surface pressure in a region 30% from the oxidant gas outlet side of the oxidant gas flow channel, which is the downstream side 50 in the oxidant gas flow direction. However, the range in which the concentration overvoltage becomes dominant varies depending on the supply rate of oxidant gas F, the specifications of the oxidant gas flow channel, and the ease of supplying oxidant gas F to the power generation section, which is determined by the specifications of the GDL, and therefore the optimal value for the design of the surface pressure distribution changes. Therefore, the surface pressure distribution may be designed depending on these conditions. [Explanation of symbols]

[0031] 10. Oxidant gas flow path 20 Oxidant gas flow path 30 Oxidant gas flow path 40 Upstream side of oxidizer gas flow direction 50 Downstream of the oxidizer gas flow 100 Cathode separator 200 Cathode Separator 300 Cathode Separator F Oxidant gas

Claims

1. A fuel cell, the fuel cell has at least a power generation unit and a pair of separators that sandwich the power generation unit; The pair of separators have grooves that form flow paths, the power generation section includes a gas diffusion layer, A fuel cell, wherein in the region of the power generation section, the surface pressure on the upstream side in the flow direction of the oxidizing gas is greater than the surface pressure on the downstream side in the flow direction of the oxidizing gas.

2. 2. The fuel cell according to claim 1, wherein, when the gas diffusion layer is not pressurized, a thickness of the gas diffusion layer on an upstream side in the flow direction of the oxidizing gas is greater than a thickness of the gas diffusion layer on a downstream side in the flow direction of the oxidizing gas.

3. 2. The fuel cell according to claim 1, wherein the density of the gas diffusion layer on the upstream side in the flow direction of the oxidizing gas is greater than the density of the gas diffusion layer on the downstream side in the flow direction of the oxidizing gas.

4. 2. The fuel cell according to claim 1, wherein the depth of the grooves on the upstream side in the flow direction of the oxidizing gas is greater than the depth of the grooves on the downstream side in the flow direction of the oxidizing gas.

5. one of the pair of separators is a cathode separator and the other is an anode separator; the cathode separator has the groove that forms an oxidant gas flow path, 2. The fuel cell according to claim 1, wherein the upstream side in the flow direction of the oxidant gas is a region of 30% to 70% from the oxidant gas inlet side of the oxidant gas flow channel, when the entire area of the oxidant gas flow channel is 100%.

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