CN110797548A

CN110797548A - Foam fuel cell without cathode gas diffusion layer

Info

Publication number: CN110797548A
Application number: CN201910953468.5A
Authority: CN
Inventors: 焦魁; 谢旭; 查森
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2019-10-09
Filing date: 2019-10-09
Publication date: 2020-02-14

Abstract

The invention discloses a foam fuel cell without a cathode gas diffusion layer, which comprises two structural forms, wherein one form is as follows: the anode current collector, the anode flow field plate, the anode gas diffusion layer, the anode microporous layer, the membrane electrode, the cathode microporous layer, the foam layer and the cathode current collector are arranged and installed into a whole in sequence and are arranged in a battery clamp. In another difference, foam layers are respectively arranged below the anode current collecting plate and above the cathode current collecting plate. The metal foam is embedded in graphite, or a metal block, forming a foam layer. The foam fuel cell improves the porosity on the premise of enhancing the heat conduction and the electric conductivity, and enhances the concentration and the uniformity of reaction gas in a catalyst layer. On the other hand, a large amount of water can be stored in the foam layer, so that blockage is not easy to form, the problem of flooding is relieved, and the self-humidifying function is also realized. And the light weight of the foam greatly improves the specific mass power and the specific volume power of the battery.

Description

Foam fuel cell without cathode gas diffusion layer

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to a structural device for removing a cathode gas diffusion layer in a proton exchange membrane fuel cell.

Background

Proton Exchange Membrane Fuel Cells (PEMFC) have been considered as one of the clean energy sources for the future transportation industry, withHigh energy density, high energy conversion efficiency, low operating temperature, fast response, zero emission and the like. The water heat management inside the fuel cell is very complicated, and the influence of the reactant concentration and the water distribution on the cell performance is great. The key to the operation of pem fuel cells is the need to maintain a high ionic conductivity (necessary water content) and water discharge balance of the membrane, otherwise slow ion transport or flooding can occur which impedes gas transport and consequently reduces output power and cell life. With the development of the core technology of the membrane electrode of the fuel cell, the effective reaction area and the current density of the cell can be further improved (reaching 1.5A cm)^-2Even higher). It is expected that as the effective reaction area and current density of the cell increase, the gas concentration and uniformity of reactants in the catalytic layer and the water produced by the reaction affect the heat and mass transfer inside the cell, and the current ridge flow channel is difficult to meet the demand of fuel distribution. Especially, the gas cannot be uniformly distributed under the ridge due to the reduction of the compression pores, and the liquid water is difficult to discharge. Therefore, the optimization and improvement of the flow passage are very important.

In addition, a gas diffusion layer (carbon paper/carbon cloth structure) is one of the essential key components of a fuel cell. The main functions are as follows: (1) the porosity ensures that the gas in the flow channel smoothly enters the catalyst layer; (2) conductivity, high conductivity reduces electron transport resistance; (3) the heat conductivity is adopted, so that the reaction heat is led out, and the structural damage of the proton exchange membrane is avoided; (4) hydrophobicity, facilitating drainage of water inside the battery; (5) support, support the overall structure of the MEA. The materials of the diffusion layer are currently produced mainly by Toray, Ballard, canada, and SGL, germany, which costs one fifth of the total fuel cell. Finding lower cost gas dispersion materials or removing gas diffusion layers is of great importance to reduce the cost of fuel cells.

Foams such as metal/carbon are a new type of porous material, and are metal/carbon scaffolds formed by irregularly connecting a plurality of open-cell hollow polyhedral cells, and have been widely used in various fields such as aerospace and aviation. Compared with the traditional metal material, the metal/carbon foam and the like have more advantages: lightweight, high porosity (often above 90%) and high specific surface area, excellent heat transfer characteristics, and high strength.

As mentioned above, the conventional fuel cell ridge channel cannot meet the distribution of reactants at high current density and the requirement of rapid discharge of generated water, and the high air permeability, electrical conductivity and thermal conductivity of the foam can solve the above problems. In addition, the foam is used for replacing the traditional flow channel and the gas diffusion layer, so that the performance of the battery can be improved on the premise of enhancing the hydrothermal transmission in the battery, the weight of the battery can be reduced, the assembly is simple and convenient, and the cost of the battery can be reduced. In addition, the foam can be beneficial to water storage and is not easy to block, so that the flooding problem is relieved, and the self-humidifying function is also realized.

The invention provides a foam fuel cell without a cathode gas diffusion layer, which can effectively solve the heat and mass transfer problem of the fuel cell under high current density, effectively improve the performance of the fuel cell, simplify the structure of the cell, reduce the cost of the fuel cell and the like.

Disclosure of Invention

The invention aims to provide a fuel cell structure device without a cathode gas diffusion layer, wherein a microporous layer is sprayed on porous metal foam to replace the conventional ridge flow channel, the gas diffusion layer and the microporous layer, so that the performance of a fuel cell is improved, and the cost of the fuel cell is reduced.

The technical scheme adopted by the invention for realizing the purpose is as follows: a foam fuel cell without a cathode gas diffusion layer has: the anode current collector, the anode flow field plate, the anode gas diffusion layer, the anode microporous layer, the membrane electrode, the cathode microporous layer, the metal foam, the foam layer, the cathode current collector, the graphite, the metal block and the like. The membrane electrode comprises: anode catalysis layer, proton exchange membrane, cathode catalysis layer. The technical scheme of the fuel cell comprises two structural forms, wherein the first structure is as follows: the anode current collector, the anode flow field plate, the anode gas diffusion layer, the anode microporous layer, the membrane electrode, the cathode microporous layer, the foam layer and the cathode current collector are arranged and installed into a whole in sequence and are arranged in a battery clamp. The second structure is as follows: the battery comprises an anode current collecting plate, a first foam layer, an anode microporous layer, a membrane electrode, a cathode microporous layer, a second foam layer and a cathode current collecting plate, wherein all the components are arranged and installed into a whole in sequence and are arranged in a battery clamp.

The second structure differs from the first structure in that: in the second structure, an anode flow field plate and an anode gas diffusion layer are removed, and two foam layers are respectively arranged at the upper end and the lower end of an anode microporous layer, a membrane electrode and a cathode microporous layer. And embedding the metal foam into the graphite or metal block to form a foam layer, wherein the foam layer is positioned between the micro-porous layer and the flow collecting plate.

At the anode, fuel enters the cell through an inlet of a flow field plate or a foam layer to reach an anode catalyst layer, and hydrogen is subjected to oxidation reaction under the action of a catalyst to generate protons and electrons; at the cathode, air enters the cell through the foam layer inlet to the cathode catalytic layer. The proton reaches the cathode catalyst layer through the proton exchange membrane and reacts with the air at the cathode to generate water, and the electron reaches the cathode through an external circuit to form a passage. On the premise of enhancing heat conduction and electric conductivity, the foam fuel cell without the gas diffusion layer slows down the gas flow rate and improves the concentration and uniformity of reaction gas in the catalyst layer, and on the other hand, a large amount of water can be stored in the foam layer, so that the foam fuel cell is not easy to block, the flooding problem is relieved, and the self-humidifying function is also realized.

The characteristics and the beneficial effects of the invention are as follows:

(1) the higher porosity of the foam layer is a potential gas redistribution medium, the more uniform distribution of reactant gas concentration after water flows through the foam, and the slower flow rate increases the residence time of reactant gas in the cell and thus increases diffusion. The internal porous and irregular framework structure can enhance the disturbance of gas, promote reaction gas to enter the catalyst layer, avoid the condition that local reactants are lacked in the traditional ridge flow field and improve the utilization rate of the reaction gas.

(2) The foam layer can store a large amount of water and is not easy to block, thereby not only relieving the flooding problem, but also playing the role of self-humidification.

(3) The metal foam has good electrical conductivity and thermal conductivity, and compared with the traditional ridge flow channel, the ohmic resistance of the battery is smaller, the temperature gradient of the battery is lower, and the output performance and the durability of the battery are effectively improved.

(4) The gas diffusion-free layer not only reduces the resistance value, but also simplifies the battery assembling procedure, reduces the cost of the fuel battery, and greatly improves the specific mass power and the specific volume power of the battery due to the lightweight of the foam.

Drawings

FIG. 1 is a schematic diagram of a first structure of the invention.

FIG. 2 is a schematic diagram of a second embodiment of the invention.

FIG. 3 is a graph comparing the performance of examples of the present invention and comparative examples.

FIG. 4 is a graph comparing the performance of examples of the invention at different cathode humidities.

FIG. 5 is a graph comparing the performance of examples of the present invention at different foam porosities.

Detailed Description

The structure of the present invention will be further described with reference to the accompanying drawings and specific embodiments, which are intended to be illustrative rather than limiting and should not be construed as limiting the scope of the present invention.

The foam fuel cell without the cathode gas diffusion layer comprises two structural forms, wherein the first structure is as follows: the anode flow field plate comprises an anode current collecting plate 1, an anode flow field plate 2, an anode gas diffusion layer 3, an anode microporous layer 4, a membrane electrode 5, a cathode microporous layer 6, a foam layer 7 and a cathode current collecting plate 8, wherein the components are arranged and installed into a whole in sequence and are placed in a battery clamp. The second structure is as follows: the battery comprises an anode current collecting plate, a first foam layer 7-1, an anode microporous layer, a membrane electrode, a cathode microporous layer, a second foam layer 7-2 and a cathode current collecting plate, wherein all the components are arranged and installed into a whole in sequence and are placed in a battery clamp. A conventional fuel cell has a structure in which a cathode gas diffusion layer is provided between a cathode microporous layer and a cathode flow field plate.

The metal foam is embedded in a graphite, or metal block, forming a foam layer. The porosity of the foam layer is 70-98%. The invention is embodied using metal foam.

The flow field plate with the traditional structure is generally in a groove-ridge structure, and the current collecting plate is a copper-plated gold plate with a smooth surface. The height of the flow channel is 1mm, the width of the groove and the ridge is 1mm or smaller, the flow field plate is a traditional parallel flow channel, and the area of the groove and ridge area is 5cm multiplied by 335 cm. During cell operation, anode fuel passes through the gas diffusion layer, the microporous layer to the catalytic layer via flow channels in the flow field plate or through the microporous layer to the catalytic layer via the foam layer, and cathode air passes through the microporous layer to the catalytic layer via the foam layer.

The main function of the foam in the gas diffusion layer-free foam fuel cell is to increase the reactant concentration of the catalytic layer and to perform the function of self-humidification. Compared with the traditional fuel cell structure, the foam with high porosity (more than 90 percent) slows down the gas flow rate, increases the concentration of reaction gas in the catalyst layer, and the internal complex porous structure also increases the uniformity of gas distribution. Because a large amount of water can be stored in the foam layer, the blockage is not easy to form, the flooding problem is relieved, and the self-humidifying function is also realized.

The three embodiments of the invention all adopt the structural form shown in figure 1, the foam area is 5cm multiplied by 5cm, and the thickness is 1 mm.

The invention is compared with the conventional structure (with cathode gas diffusion layer) in which a fuel cell is assembled. The materials and structures of the rest components of the two batteries are completely the same except for the cathode flow field area. The thickness of the anode catalytic layer is 3 μm (platinum loading 0.2mg cm)^-2) The thickness of the cathode catalytic layer was 6 μm (platinum loading 0.4mg cm)^-2) The microporous layer was 20 μm. After completely identical activation procedures (running for 6.5H at 0.45V) the two cells were tested under the same working conditions, the cells were run in constant current mode with anode fuel H₂The cathode gas is air, the inlet air temperature is 70 ℃, the inlet air humidity is 80%, the inlet air flow of the anode is 0.5SLPM, the inlet air flow of the cathode is 1.5SLPM, and the outlet pressure of the cathode and the anode is one atmosphere.

The foam layer of example 1 had a porosity of 90%.

Fig. 3 shows the polarization curves and power densities of two cells, and it can be seen that the performance of the foam cell without cathode gas diffusion layer is greatly improved compared with the conventional structure cell.

This example shows the polarization curve and power density curve for a metal foam flow field versus a conventional parallel flow field fuel cell at 80% cathode and anode humidity. It can be seen that the peak power density of the conventional parallel flow field fuel cell is 0.25Wcm^-2And the peak power density of the metal foam flow field battery is 0.73W cm^-2And the improvement is three times. The limiting current density was also from 0.6A cm when the cell cathode used a metal foam flow field^-2Lifting to 1.8A cm^-2. Although both parallel flow channel and metal foam flow channel fuel cells exhibit significant mass transport losses, the foam flow channels appear later than the parallel flow channel fuel cells. Therefore, the metal foam flow field is used as the cathode of the battery, so that the mass transfer loss of the battery can be effectively reduced, and the power density of the battery is improved.

Example 2, the same experimental parameters as in example 1, but with a 100% inlet humidity, the porosity of the metal foam was 80%.

Fig. 4 shows the cell polarization curve and power density for the case of 80%, 60%, 40%, and 20% cathode humidity for a non-cathode gdl foam fuel cell with 80% anode inlet humidity. The cell was operated in galvanostatic mode with anode fuel H₂The cathode gas is air, the anode inlet flow is 0.5SLPM, the cathode inlet flow is 1.5SLPM, and the cathode outlet pressure and the anode outlet pressure are both one atmosphere.

This example gives the polarization curve and power density curve for a metal foam flow field fuel cell when the cathode inlet gas humidity drops from 80% to 20%. As the cathode inlet gas humidity decreased from 80% to 20%, the cell performance showed a tendency to rise first and then fall. The cell achieved the best output performance at 80% anode and 60% cathode relative humidity. The reason is that cathode flooding is gradually relieved when the cathode inlet gas humidity is reduced from 80% to 60%. But as the cathode inlet gas humidity drops further, the catalytic layers and membranes gradually dry out, resulting in increased polarization losses and ohmic losses. The battery shows the worst performance under the working conditions of 80 percent of anode and 20 percent of cathode, but the battery still has 0.62W cm^-2The output performance of the device is 0.25W cm when compared with the traditional parallel flow channel when the cathode and the anode are RH 80%^-2In contrast, it is still much higher. The low pressure drop and gas flow rate of the metal foam cause the weak water discharge capacity, reduce the dependence of the battery on the inlet air humidity and play a role in self-humidification.

It was found that the reduction of cathode humidity had minimal effect on cell performance, with the best performance operating conditions being anode RH 80%/cathode RH 60%, indicating that the use of a foam layer effectively reduced the cell's dependence on inlet humidity.

Fig. 5 shows the cell polarization curve and power density for the cathode foam porosity conditions of 90% (example 1), 80% (example 2), and 70% (example 3), respectively.

The inlet humidity of the cathode and the anode are both 100%, the anode uses parallel flow channels, the cell operates in a constant current mode, and the anode fuel is H₂The cathode gas is air, the inlet air temperature is 70 ℃, the inlet air humidity is 100%, the inlet air flow of the anode is 0.5SLPM, the inlet air flow of the cathode is 1.5SLPM, and the outlet pressure of the cathode and the anode is one atmosphere. It was found that the higher the porosity of the foam, the higher the performance, but all the better the parallel flow field fuel cell performance.

This example gives the polarization curves and power density curves for fuel cells with cathode metal foam porosity of 0.9,0.8 and 0.7. It can be seen that the battery performance gradually increases as the porosity increases. This is mainly because as the porosity rises, the reactant gas is distributed more evenly, and the space in which the foam can be used for storing water becomes larger, increasing the gas concentration while reducing the occurrence of flooding. Therefore, low humidity and high porosity are of paramount importance for metal foam fuel cells.

Claims

1. A foam fuel cell without a cathode gas diffusion layer, having: the anode current collector, anode flow field plate, anode gas diffusion layer, anode micropore layer, membrane electrode, cathode micropore layer, metal foam, foam layer, and cathode current collector, still include graphite, metal block, the membrane electrode includes: anode catalysis layer, proton exchange membrane, cathode catalysis layer, its characterized in that: the fuel cell comprises two structural forms, wherein the first structure is as follows: the anode flow field plate comprises an anode current collecting plate (1), an anode flow field plate (2), an anode gas diffusion layer (3), an anode microporous layer (4), a membrane electrode (5), a cathode microporous layer (6), a foam layer (7) and a cathode current collecting plate (8), wherein all components are sequentially arranged and installed into a whole and are placed in a battery clamp; the second structure is as follows: the anode current collector, the first foam layer (7-1), the anode microporous layer, the membrane electrode, the cathode microporous layer, the second foam layer (7-2) and the cathode current collector are sequentially arranged and installed into a whole and are placed in a battery clamp.

2. The cathode gas diffusion layer-free foam fuel cell according to claim 1, wherein: the metal foam is embedded in graphite or a metal block to form a foam layer.

3. The cathode gas diffusion layer-free foam fuel cell according to claim 1 or 2, characterized in that: the porosity of the foam layer is 70% -98%.