JP5130686B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to a separator made of a conductive porous body.

  The polymer electrolyte fuel cell is an electrolyte membrane / electrode catalyst composite in which a solid polymer electrolyte membrane and both sides thereof are coated with a fuel electrode (hereinafter referred to as an anode) catalyst layer and an oxidant electrode (hereinafter referred to as a cathode) catalyst layer. Are sandwiched between gas diffusion layers made of a porous carbon material. Further, a plurality of unit cells each having a separator for supplying fuel gas and oxidant gas are arranged on both sides to form a laminated body, and both ends of the laminated body are clamped by a clamping plate to form a fuel cell. Configure the cell stack. This fuel cell stack is stacked and installed such that the in-plane direction of the electrolyte membrane / electrode catalyst composite is perpendicular to the horizontal direction.

  The separator has a corrugated shape with a flow path groove for fuel gas or oxidant gas on one side and a cooling water flow path groove on the other side. In the fuel cell using this separator, the convex surface of the fuel gas channel is in contact with the gas diffusion layer on the anode side, and the convex surface of the oxidant gas channel is in contact with the cathode side. At this contact portion, the electrons generated by the reaction are transferred, and the heat generated by the electrochemical reaction is transferred to the cooling water. Further, the fuel gas or oxidant gas flows through the recess and is supplied to the catalyst electrode via the gas diffusion layer. The cooling water is formed by concave portions facing each other when the convex surfaces on the cooling water flow path side of two adjacent separators are in contact with each other.

  In the polymer electrolyte fuel cell, hydrogen in the fuel gas flowing through the separator channel diffuses in the gas diffusion layer, and when it reaches the anode, it emits electrons by a catalytic reaction to become protons. Proton moves from the anode side to the cathode side through the solid polymer electrolyte membrane, but electrons cannot move from the anode side to the cathode side, so it passes through an external circuit via a conductive gas diffusion layer and a separator. Move to the cathode side.

  On the other hand, on the cathode side, protons moved through the solid polymer electrolyte membrane, electrons sent from an external circuit, and the oxidant gas (air) flowing through the separator channel and diffusing in the gas diffusion layer. Reacts with oxygen to produce water. Most of the generated water evaporates in the unreacted gas and is directly discharged out of the cell stack, but remains as liquid phase water in a supersaturated state. When liquid phase water generated by the electrochemical reaction oozes out from the gas diffusion layer, it is conceivable that the liquid phase water stays in the reaction gas flow path and hinders diffusion of the reaction gas. In Patent Document 1, a separator is formed of a porous material, and water that has oozed out of the gas diffusion layer is effectively moved to prevent the reaction gas passage from being blocked.

JP-A-2005-142015

  In the conventional fuel cell structure, when the fuel gas or the oxidant gas is supplied to the electrode catalyst, the fuel gas or the oxidant gas is supplied to the gas diffusion layer from the gas flow path formed by the separator recess. However, the separator projections in contact with the gas diffusion layer do not sufficiently diffuse the gas, and there is a possibility that the gas supply becomes non-uniform in the surface of the electrode catalyst layer. Similarly, when fuel gas or oxidant gas cannot be evenly distributed to a plurality of gas flow paths, it is difficult to supply the electrode catalyst uniformly with only the gas diffusion layer. As described above, when the fuel cell is operated at a high current density in a situation where the reactant gas cannot be supplied uniformly, the reactant gas is deficient at a portion where the flow rate is small, and the output voltage is lowered. Furthermore, the in-plane distribution of the reaction gas supplied to the separator also leads to the generation of an in-plane distribution of heat generated by the electrochemical reaction. In particular, in high current density operation, the temperature increases at the part where the reaction gas supply is large, which causes a local decrease in the service life of cell components such as solid polymer electrolyte membranes. There is a problem that the range cannot be set wide.

  Water generated by an electrochemical reaction at the cathode electrode is discharged to the separator channel through the gas diffusion layer. When the discharged water closed the separator channel, gas could not be supplied through the channel, leading to a decrease in output.

  In the corrugated channel structure, only the convex portion of the separator channel groove is in contact with the gas diffusion layer or the adjacent separator. For this reason, compared with the power generation area, the contact area between the separator and the gas diffusion layer is reduced, and the loss due to the increase in the contact electrical resistance has led to a decrease in the fuel cell output.

The fuel cell of the present invention, the fuel gas and the oxidant gas flow path of the separator, applying a porous body consisting of multiple several layers that have a different pore size distributions. By adopting such a configuration, it is possible to secure a flow path necessary for holding the generated water and gas diffusion. In addition, the contact area between the electrolyte membrane and electrode catalyst composite is increased by applying a porous material, and the gas is supplied uniformly to the electrode catalyst, and the contact electrical resistance is reduced, and the output density is reduced. It is possible to improve. Furthermore, the heat transfer characteristics are improved by increasing the contact area, and the heat generated by the power generation can be transmitted uniformly and quickly to the cooling unit.

According to the present invention, by constructing the separator gas flow path from the porous body made of double several layers, by a separation coexistence of water and the reaction gas resulting liquid phase in the power generation reaction, high even at a high current density Provided is a fuel cell capable of efficient power generation.

  First, items common to all the embodiments will be described. Moreover, the separator which consists of two layers is demonstrated as an Example.

In the separator of the present invention, a gas-impermeable layer that separates two kinds of fluids and a reactive porous body in all or part of the reaction gas flow path are provided, for example, iron, aluminum, nickel, titanium, magnesium. , chromium, molybdenum and formed from these alloys, the porous body, the pore diameter and porosity and a different Do that multiple several layers. Here, at least one porous layer has two pore size distributions, and the other layer has a single pore size distribution.

As an example of the pore distribution measurement of the porous body, it is possible to apply a mercury intrusion method. The pore distribution measurement by the mercury intrusion method is a method for calculating the volume of the pores based on the volume of mercury that has entered the pores, and is performed as follows. Put a porous material in a container for measurement, and fill the container with mercury. When pressure is applied to the mercury liquid surface, mercury gradually fills from the large pores of the porous body to the small pore diameter. For the calculation of the pore diameter, the relationship between the applied pressure and the pore diameter through which mercury can enter at that pressure is used as shown in the following equation.
D = -4γcosθ / P
Here, D is the pore diameter, γ is the surface tension of mercury, θ is the contact angle between the pore wall and mercury, and P is the pressure.

  The porous body in the present invention is composed of a porous body having a single pore size distribution and a porous body having two pore size distributions. The porous body having a single pore size distribution is to have one maximum value in the relationship between the pore diameter obtained by the pore distribution measurement as shown in FIG. 1 and the log differential pore volume, The two pore diameter distributions indicate that the relation between the pore diameter obtained by the pore distribution measurement as shown in FIG. 2 and the log differential pore volume has two maximum values.

  As the relationship of the pore diameter of the porous body in the present invention, a porous body having a single pore diameter distribution has a relatively largest pore diameter distribution. The porous body having two pore size distributions has a relatively large pore size and a relatively small pore size. As the pore diameter of the porous body having two pore diameter distributions, the relatively large pore diameter is desirably 5 μm or more.

  As an example of a method for producing a porous body having two pore size distributions, metal powder made of the above-described metal is used. In order to transport the generated water by capillary force, a metal powder having a small particle size and an average particle size of 200 μm or less, preferably 100 μm or less are used. Resin that evaporates at a specified temperature is mixed into the metal powder. The mixed resin evaporates by the heat treatment, and holes for holding the reaction gas flow path and the generated water are formed. For this reason, it becomes possible to form pores of an arbitrary size depending on the particle diameter of the mixed resin.

  In the present invention, as described above, the resin is formed from two kinds of holes for holding the generated water and the holes for forming the reaction gas channel, and therefore, at least two kinds of resin having a particle diameter are mixed therein. These are printed or sprayed on a flat plate made of the metal and heat-treated to evaporate the resin, thereby forming a porous body. It is also possible to degrease and sinter metal powder mixed with resin powder to form a porous body, which can be joined on a flat plate by laser welding.

  In order to form a porous body having a single pore size distribution, the particle diameter of the resin mixed in the method for producing a porous body may be made substantially equal.

  The relationship between the thicknesses of the two porous layers is such that the thickness of the porous layer having a single pore size distribution is ½ or more of the total thickness. This is because the flow in the surface direction of the reaction gas is mainly in a porous body having a single pore size distribution, so that the pressure loss is not increased more than necessary.

Regarding the wettability of the porous body, a porous body having a single pore size distribution is subjected to a hydrophobic treatment, and a porous body having two pore diameter distributions is subjected to a hydrophilic treatment. As a hydrophobic treatment method, for example, a dispersion containing polytetrafluoroethylene (PTFE), which is a fluororesin, is diluted to an appropriate concentration and impregnated or coated. Thereafter, firing is performed at 275 ° C. or higher where PTFE melts and 750 ° C. or lower where PTFE decomposes. As a hydrophilic treatment method, for example, a hydrophilic substance such as TiO ₂ is impregnated or applied.

  Since the wettability can be evaluated by the contact angle of water droplets on the surface, the contact angle of a porous body having a single pore size distribution is φ1, and the contact angle of a porous body having two pore size distributions is φ2. Then, a water repellent treatment satisfying φ2 <φ1 may be performed. However, when the contact angle is around 90 °, it becomes the boundary between water absorption and drainage due to the capillary force of the pores, so in order to move moisture reliably, the contact angle of the porous body having a single pore diameter distribution is A range of 100 ° <φ1 <180 ° is preferable.

  Hereinafter, detailed embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a cross-sectional view of the first embodiment of the present invention. Here, the porous layer 4 having a single pore size distribution is provided on the gas-impermeable layer 1 side, and the porous layer 3 having two pore size distributions is provided on the electrolyte membrane / electrode catalyst composite 2. The separator is composed of a gas-impermeable layer 1, a first porous layer 3, and a second porous layer 4, both of which are formed of a conductive material such as a metal. The electrolyte membrane / electrode catalyst composite 2 is a portion that generates water, electricity, and heat by electrochemical reaction from H ⁺ , e ^−, and O ₂ , and the porous body anode channels 3 a and 4 a are made of a fuel gas containing hydrogen, The portion to be sent to the electrolyte membrane / electrode catalyst composite 2, the porous body cathode channels 3 b and 4 b are the portions to send the oxidant gas containing oxygen to the electrolyte membrane / electrode catalyst composite 2, and the gas impermeable layer 1 is cooled Physical separation of water and reaction gas to prevent gas leakage.

  The porous layers 3 and 4 are formed of porous bodies having different porosity or pore diameter. The first porous layers 3a and 3b in contact with the electrolyte membrane / electrode catalyst composite 2 are porous bodies having two pore diameter distributions, and the porous layers 4a and 4b in contact with the gas-impermeable layer 1 are a single porous layer. It is a porous body having a pore size distribution. The operation of the fuel cell in this configuration is as follows.

  The supplied fuel gas first enters the porous anode channels 3a and 4a of the separator. Since the porous layer 4a having a single pore size distribution is larger than the porous layer 3a having two pore size distributions in terms of both porosity and pore size, most of the flow in the separator surface direction has a single pore size distribution. It flows through the porous layer 4a.

  The fuel gas flowing in the porous layer 4a is diffused also in the direction perpendicular to the surface of the separator by the porous flow path communicating in various directions. The fuel gas that has reached the porous layer 3a reaches the electrolyte membrane / electrode catalyst composite 2 through a hole having a relatively large diameter.

  Then, it becomes a proton by an electrochemical reaction on the catalyst of the electrolyte membrane / electrode catalyst complex 2 and generates electric power by releasing electrons. Protons move to the cathode side through the electrolyte membrane. Unreacted gas is discharged from the fuel gas outlet. Similarly, the supplied oxidant gas also diffuses from the porous layer 4b having a single pore distribution toward the electrolyte membrane / electrocatalyst composite 2 in the porous layer 3b having two pore diameter distributions. Therefore, it combines with the protons and electrons supplied via an external circuit to produce water and heat. This water is discharged to the porous layer 3b having two pore size distributions. A part of the water is also discharged to the anode side by the electroosmotic flow or the osmotic flow based on the concentration difference, and thus is discharged to the porous layer 3a having two pore diameter distributions. The heat is cooled and removed by water flowing through the cooling water flow path 6.

  The electric charge generated by the electrochemical reaction on the anode side of the electrolyte membrane / electrode catalyst composite 2 is supplied to an external load through the porous anode flow paths 3a and 4a, the gas impermeable layer 1, and the like. At this time, a contact electric resistance is generated at the contact surface of each component of the fuel cell, which leads to a loss of electric energy extracted to the outside. In the separator applied to the fuel cell in the present invention, the contact area between the electrolyte membrane / electrode catalyst composite 2 and the porous layer 3 having two pore diameter distributions increases, which contributes to the reduction of the contact electric resistance, and the fuel The battery can be made highly efficient.

  When the water generated by the power generation is condensed on the electrode surface by adopting the configuration as in this example, the electrode catalyst layer and the porous layer have two pore diameter distributions due to the difference in wettability between the electrode catalyst layer and the porous layer. It is possible to move to the porous layer 3. Further, the liquid-phase water that has moved to the porous layer 3 having two pore size distributions moves to pores having a small pore size due to the capillary force due to the difference in pore size inside the porous material. At this time, since the porous body has been subjected to a hydrophilic treatment, water moves along the metal surface constituting the porous body. For this reason, it is possible to maintain the role of a relatively large diameter hole as a reaction gas diffusion channel.

  When a conventional fuel cell is operated at a high current density, the amount of water produced by the reaction is increased, the gas flow path is blocked, and the power generation voltage is lowered. In the fuel cell using the separator of the present invention, the generated water and the reaction gas are separated from each other, so that a decrease in the generated voltage can be suppressed when operating at a high current density as compared with a fuel cell having a conventional separator configuration. In particular, it is effective to apply the present invention as an oxidant gas side separator that produces a large amount of produced water.

  The water held in the relatively small-diameter holes can be used for humidification when the reaction gas becomes insufficiently humidified, and further supplies water so that the electrolyte membrane / electrode catalyst complex 2 does not become insufficiently moisture. I can do it. Therefore, the separator having the configuration as in the present embodiment has a water management function. In the case of a fuel cell using a separator having such a configuration, the introduced reaction gas can be supplied with low humidification, and the load on the humidifying portion of the fuel cell system can be reduced.

  In the second embodiment of the present invention, as shown in FIG. 4, the porous layer 4 having a single pore size distribution that has been subjected to hydrophobic treatment is disposed on the side of the electrolyte membrane / electrode catalyst complex 2 with two finely-treated hydrophilic layers. The porous layer 3 having a pore size distribution is provided in the gas impermeable layer 1.

  With such a configuration, when the water condensed on the electrode catalyst is discharged to the porous layer 4 having a single pore size distribution, the inside of the hydrophobic-treated porous material moves quickly, and the two fine particles are moved. It is possible to move to the porous layer 3 having a pore size distribution or downstream, and blockage of the flow path by generated water can be prevented. In the porous layer 3 having two pore size distributions, moisture can be retained in the same manner as in Example 1, and the reaction gas can be humidified. Such a configuration is effective for a fuel cell that operates at a high current density with a large amount of produced water.

  A third embodiment of the present invention is shown in FIG. In the present embodiment, the fuel gas and the oxidant gas are in the case of opposing flows. As for the structure of the porous body, both the fuel gas and the oxidant gas have a porous layer having two pore diameter distributions on the upstream side of the flow path on the electrolyte membrane / electrode catalyst composite 2 side and a gas impermeable layer on the downstream side. Provided on one side.

  Even if a uniform power generation reaction occurs in the separator surface, the generated water tends to stay downstream due to the gas flow. Therefore, the electrolyte membrane is easily dried in the upstream portion of the separator, and the gas flow path is likely to be blocked by the generated water on the downstream side.

  By configuring the porous layer as in the present embodiment, the generated water is retained on the side of the electrolyte membrane / electrode catalyst complex 2 upstream of the reaction gas flow, and drying of the electrolyte membrane is prevented downstream. The porous layer having a single pore size distribution that has been subjected to hydrophobic treatment can quickly move the generated water to the outlet layer or the porous layer having two pore size distributions. It can be prevented.

  From upstream to downstream, the reaction gas is gradually consumed by the power generation reaction. In the case of a separator with insufficient gas diffusibility, gas supply to the electrode catalyst layer is insufficient downstream, and the power generation reaction is biased within the separator surface. In the configuration of this example, since the porous layer having a single pore size distribution that mainly plays the role of the gas flow path on the downstream side is disposed on the electrolyte membrane / electrode catalyst composite 2 side, the electrode catalyst layer The gas diffusivity can be maintained and stable power generation is possible.

  The effect of this example is that, even if the reaction gas flows are in the same direction and orthogonal directions, the porous layer having two pore diameter distributions upstream is on the electrolyte membrane / electrode catalyst complex 2 side, and the gas impermeable on the downstream side It is effective to provide it on the layer 1 side.

The relationship between the pore diameter of the porous body which has a single pore diameter concerning a present Example, and a log differential pore volume. The relationship of the pore diameter and log differential pore volume of the porous body which has two pore diameters concerning a present Example. 1 is a schematic plan view showing an electrolyte membrane / catalyst electrode complex side structure of a separator applied to a first embodiment of a fuel cell according to the present invention. The typical top view which shows the electrolyte membrane and catalyst electrode composite side structure of the separator applied to 2nd embodiment of the fuel cell concerning this invention. The typical top view which shows the electrolyte membrane and catalyst electrode composite side structure of the separator applied to 3rd embodiment of the fuel cell concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas impermeable layer 2 Electrolyte membrane and electrode catalyst composite body 3 Porous body which has two pore diameter distribution 4 Porous body which has single pore diameter distribution 5 Separator cooling water side porous rib 6 Cooling water flow path

Claims (4)

An electrolyte membrane / electrode catalyst composite in which a proton conductive electrolyte is sandwiched between a fuel electrode and an air electrode, a first conductive separator having a fuel gas flow path for supplying fuel gas to the fuel electrode, and the oxidation In a fuel cell having a second conductive separator having an oxidant gas supply channel for supplying an oxidant gas to the agent electrode,
Said first conductive separator及beauty before Symbol second conductive separator in contact with the porous body formed from a plurality of layers in the thickness direction, and the membrane electrode catalyst composite of the porous body have a gas impermeable layer separating the two fluids, which is disposed on a surface opposite to the surface,
The porous body has a first porous layer having two or more different pore size distributions whose surfaces and inside are subjected to hydrophilic treatment, and a first pore layer having a single pore size distribution whose surfaces and inside are subjected to water repellent treatment. 2 porous layers, the pore diameter of the second porous layer is larger than the pore diameter of the first porous layer,
The fuel cell, wherein the fuel gas or the oxidant gas flows through pores of the porous body . 2. The fuel cell according to claim 1 , wherein the first porous layer is disposed in contact with the electrolyte membrane / electrode catalyst composite. 2. The fuel cell according to claim 1 , wherein the first porous layer is disposed on the gas impermeable layer side. Claim 1 wherein the first porous layer is in the upstream side of the reaction gas stream are arranged in the membrane electrode catalytic composite side, the downstream side of the reaction gas stream, characterized in that arranged in the gas-impermeable layer side A fuel cell according to claim 1.

Images