CN110797548A - Foam fuel cell without cathode gas diffusion layer - Google Patents

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, in particular to a structural device for removing a cathode gas diffusion layer in a proton exchange membrane fuel cell.

Background technique

Proton exchange membrane fuel cells (PEMFCs) have always been considered as one of the clean energy sources in the future transportation industry, with the advantages of high energy density, high energy conversion efficiency, low operating temperature, fast response, and zero emissions. The internal hydrothermal management of fuel cells is very complex, and the concentration of reactants and the distribution of water have a great influence on the performance of the cells. The key to the operation of proton exchange membrane fuel cells is to maintain a balance between high ionic conductivity of the membrane (necessary water content) and water discharge, otherwise ion transport will be too slow or water flooding will hinder gas transport, thereby reducing output power and battery life. . With the development of the core technology of fuel cell membrane electrodes, the effective reaction area and current density of the cell will be further improved (reaching 1.5A cm ^-2 or even higher). It is conceivable that with the increase of the effective reaction area and current density of the battery, the gas concentration and uniformity of the reactants in the catalytic layer and the water generated by the reaction will affect the heat and mass transfer inside the battery. It will be difficult to meet the demand for fuel distribution. Especially under the ridge, due to the reduction of compressed pores, the gas cannot be evenly distributed, and the liquid water is also difficult to discharge. Therefore, the optimization and improvement of the flow channel is extremely important.

In addition, the gas diffusion layer (carbon paper/carbon cloth structure) is one of the indispensable key components of fuel cells. Its main functions are: (1) porosity, to ensure the smooth entry of the gas in the flow channel into the catalytic layer; (2) electrical conductivity, high electrical conductivity reduces electron transport resistance; (3) thermal conductivity, the heat of reaction is exported to avoid proton exchange Membrane structure destruction; (4) hydrophobicity, promoting the discharge of water inside the battery; (5) supportability, supporting the overall structure of the MEA. At present, the material of the diffusion layer is mainly produced by Toray of Japan, Ballard of Canada and SGL of Germany, and its cost accounts for one-fifth of the entire fuel cell. Finding lower cost gas dispersion materials or removing the gas diffusion layer is of great significance to reduce the cost of fuel cells.

Metal/carbon foam is a new type of porous material. It is a metal/carbon scaffold composed of many open-celled hollow polyhedral units that are irregularly connected to each other. It has been widely used in various fields such as aerospace and aviation. Foams such as metal/carbon have more advantages than traditional metal materials: light weight, high porosity (often above 90%) and high specific surface area, excellent heat transfer properties, and high strength.

As mentioned above, the traditional fuel cell ridge flow channel cannot meet the requirements of reactant distribution and rapid discharge of generated water under high current density, and the high air permeability, electrical conductivity and thermal conductivity of foam can solve the above problems. In addition, using foam to replace the traditional flow channel and gas diffusion layer can not only improve the battery performance under the premise of strengthening the water-heat transfer inside the battery, but also make the battery lighter, easier to assemble and reduce the battery cost. In addition, the foam is good for water storage and not easy to block, which not only alleviates the problem of flooding, but also plays a role in self-humidification.

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 cell structure, and reduce the cost of the fuel cell.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a fuel cell structure device without a cathode gas diffusion layer, spraying a microporous layer on the porous metal foam to replace the current ridge channel, gas diffusion layer and microporous layer, so as to improve the fuel cell performance. performance and lower fuel cell costs.

In order to achieve this purpose, the technical scheme adopted by the present invention is: a foam fuel cell without a cathode gas diffusion layer has: an anode current collector plate, an anode flow field plate, an anode gas diffusion layer, an anode microporous layer, a membrane electrode, and a cathode microporous layer. , metal foams, foam layers, and cathode current collectors, as well as graphite, metal blocks, and the like. The membrane electrode includes: an anode catalytic layer, a proton exchange membrane, and a cathode catalytic layer. The technical scheme of the fuel cell of the present invention includes two structural forms, the first structure is: anode current collector plate, anode flow field plate, anode gas diffusion layer, anode microporous layer, membrane electrode, cathode microporous layer, foam layer, As well as the cathode current collecting plate, the components are arranged in sequence and installed as a whole, and are placed in the battery fixture. The second structure is: the anode current collector plate, the first foam layer, the anode microporous layer, the membrane electrode, the cathode microporous layer, the second foam layer, and the cathode current collector plate. in the battery holder.

The difference between the second structure and the first structure is that the second structure removes the anode flow field plate and the anode gas diffusion layer, and places two foams on the upper and lower ends of the anode microporous layer, the membrane electrode and the cathode microporous layer, respectively. Floor. And the metal foam is embedded in graphite or metal block to form a foam layer, and the foam layer is located between the microporous layer and the current collecting plate.

At the anode, the fuel enters the cell through the inlet of the flow field plate or the foam layer and reaches the anode catalytic layer. Under the action of the catalyst, hydrogen undergoes oxidation reaction to generate protons and electrons; at the cathode, air enters the cell through the inlet of the foam layer and reaches the cathode catalytic layer. The protons reach the cathode catalytic layer through the proton exchange membrane to react with the air in the cathode to generate water, and the electrons reach the cathode through the external circuit to form a path. On the premise of enhancing thermal conductivity and electrical conductivity, this kind of foam fuel cell without gas diffusion layer slows down the gas flow rate due to its high porosity, and improves the concentration and uniformity of the reaction gas in the catalytic layer, on the other hand, the foam layer A large amount of water can be stored in the middle and it is not easy to form blockages, which not only alleviates the problem of flooding, but also functions as self-humidification.

The characteristics of the present invention and the beneficial effects produced:

(1) The porosity of the foam layer is high, and it is a gas redistribution medium with development potential. After the water flows through the foam, the concentration distribution of the reactant gas is more uniform, and the slow flow rate will increase the time that the reactant gas stays inside the battery and thus increase diffusion. The internal porous and irregular skeleton structure will enhance the disturbance of the gas, promote the entry of the reactant gas into the catalytic layer, prevent the local shortage of reactants in the traditional ridge flow field, and improve the utilization rate of the reactant gas.

(2) A large amount of water can be stored in the foam layer and it is not easy to form blockage, which not only alleviates the problem of flooding, but also plays a role in self-humidification.

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

(4) No gas diffusion layer not only reduces the resistance value, but also simplifies the assembly process of the battery, reducing the cost of the fuel cell, and the lightness of the foam also greatly improves the specific mass power and specific volume power of the battery.

Description of drawings

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

Figure 2 is a schematic diagram of the second structure of the invention.

FIG. 3 is a performance comparison curve diagram of the embodiment of the present invention and the comparative example.

FIG. 4 is a performance comparison curve diagram of an embodiment of the present invention under different cathode humidity.

FIG. 5 is a performance comparison diagram of the embodiments of the present invention under different foam porosity.

Detailed ways

The structure of the present invention will be further described below through the accompanying drawings and specific embodiments. It should be noted that this embodiment is descriptive rather than restrictive, and does not limit the protection scope of the present invention.

The foam fuel cell without cathode gas diffusion layer includes two structures. The first structure is: anode current collector plate 1, anode flow field plate 2, anode gas diffusion layer 3, anode microporous layer 4, membrane electrode 5, cathode The microporous layer 6 , the foam layer 7 , and the cathode current collector plate 8 are arranged in sequence and installed as a whole, and are placed in the battery fixture. The second structure is: anode current collector plate, first foam layer 7-1, anode microporous layer, membrane electrode, cathode microporous layer, second foam layer 7-2, and cathode current collector plate, the components are in order The drain is mounted as one piece and placed in the battery holder. The structure of the traditional fuel cell is that a cathode gas diffusion layer is arranged between the cathode microporous layer and the cathode flow field plate.

The metal foam is embedded in graphite or metal block to form a foam layer. The porosity of the foam layer is 70%-98%. As an example, the present invention uses a metal foam.

The flow field plate of the traditional structure is generally a groove ridge structure, and the current collector plate is a copper gold-plated plate with a flat surface. The height of the flow channel is 1mm, the width of the groove and the ridge is 1mm or less, the flow field plate is a traditional parallel flow channel, and the area of the groove and ridge area is 5cm×335cm. When the cell is in operation, the anode fuel passes through the gas diffusion layer, the microporous layer to the catalytic layer through the flow channels in the flow field plate, or through the foam layer through the microporous layer to the catalytic layer, and the cathode air passes through the foam layer and through the microporous layer to reach the catalytic layer. catalytic layer.

The main function of the foam in the gas diffusion layer-free foam fuel cell is to increase the concentration of reactants in the catalytic layer and to perform the function of self-humidification. Compared with the traditional fuel cell structure, the foam with high porosity (above 90%) slows down the gas flow rate and increases the concentration of reactive gas in the catalytic layer, and the complex porous structure inside also increases the uniformity of gas distribution. Since a large amount of water can be stored in the foam layer, it is not easy to form blockage, which not only alleviates the problem of flooding, but also plays a role in self-humidification.

The three embodiments of the present invention all adopt the structure shown in FIG. 1 , the foam area is 5cm×5cm, and the thickness is 1mm.

The invention and the traditional structure (with a cathode gas diffusion layer) were assembled into a fuel cell for comparison. Except for the difference in the cathode flow field area, the materials and structures of the remaining components of the two batteries are identical. The thickness of the anode catalytic layer is 3 μm (platinum loading 0.2 mg cm ⁻² ), the thickness of the cathode catalytic layer is 6 μm (platinum loading 0.4 mg cm ⁻² ), and the microporous layer is 20 μm. The two cells were tested under the same working conditions after the exact same activation procedure (6.5h at 0.45V), the cells were operated in constant current mode, the anode fuel was H ₂ , the cathode gas was air, and the inlet temperature was 70°C , the intake air humidity is 80%, the anode intake air flow is 0.5SLPM, the cathode intake air flow is 1.5SLPM, and the cathode and anode outlet pressures are all one atmosphere pressure.

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

Figure 3 shows the polarization curves and power density of the two batteries. It can be seen that the performance of the foam battery without cathode gas diffusion layer is greatly improved compared with the traditional structure battery.

This example shows the polarization curve and power density curve of the metal foam flow field and the traditional parallel flow field fuel cell when the humidity of both anode and cathode is 80%. It can be seen that the peak power density of the traditional parallel flow field fuel cell is 0.25Wcm ^-2 , while the peak power density of the metal foam flow field cell is 0.73W cm ^-2 , which is three times higher. When the metal foam flow field is used in the battery cathode, the limiting current density is also increased from 0.6A cm ^-2 to 1.8A cm ^-2 . Although both parallel channel and foam metal channel fuel cells show significant mass transfer losses, foam channels appear later than parallel channel fuel cells. It can be seen that using the metal foam flow field as the battery cathode can effectively reduce the mass transfer loss of the battery and improve the power density of the battery.

In Example 2, the experimental parameters are the same as those in Example 1, but the air intake humidity is 100%, and the porosity of the metal foam is 80%.

Figure 4 shows the cell polarization curve and power density of the cathode gas diffusion layer foam fuel cell when the anode inlet humidity is 80%, and the cathode humidity is 80%, 60%, 40%, and 20%, respectively. The cell operates in constant current mode, the anode fuel is H ₂ , the cathode gas is air, the anode inlet flow rate is 0.5SLPM, the cathode inlet flow rate is 1.5SLPM, and the cathode and anode outlet pressures are both atmospheric pressure.

This example presents the polarization and power density curves of a metal foam flow field fuel cell when the cathode inlet gas humidity is decreased from 80% to 20%. As the cathode inlet gas humidity decreases from 80% to 20%, the cell performance shows a trend of first increasing and then decreasing. The best output performance of the battery was obtained under the condition of anode 80% cathode 60% relative humidity. The reason is that the cathode flooding phenomenon is gradually alleviated when the cathode inlet gas humidity is reduced from 80% to 60%. However, as the humidity of the cathode inlet gas decreases further, the catalytic layer and membrane gradually dry out, resulting in higher polarization and ohmic losses. The battery shows the worst performance under the condition of 80% anode and 20% cathode, but the battery still has an output performance of 0.62W cm ^-2 , which is 0.25W cm compared with the traditional parallel flow channel when both yin and yang are RH80%. Compared with ^-2 , it is still much higher. This is mainly due to the low pressure drop and gas flow rate of the metal foam, resulting in a weak water discharge capacity, which reduces the battery's dependence on the intake air humidity and plays a role in self-humidification.

It can be found that the decrease of cathode humidity has little effect on battery performance, and the best performance is anode RH80%/cathode RH60%, indicating that the use of foam layer effectively reduces the battery's dependence on intake air humidity.

FIG. 5 shows the polarization curves and power density of the battery under the conditions of cathode foam porosity of 90% (Example 1), 80% (Example 2), and 70% (Example 3), respectively.

The air intake humidity of the cathode and anode are both 100%, the anode uses parallel flow channels, the battery operates in constant current mode, the anode fuel is H ₂ , the cathode gas is air, the intake air temperature is 70°C, and the intake air humidity is 100%. The anode inlet flow rate is 0.5SLPM, the cathode inlet flow rate is 1.5SLPM, and both the cathode and anode outlet pressures are one atmospheric pressure. It can be found that the higher the foam porosity, the higher the performance, but the performance is better than that of the parallel flow field fuel cell.

This example presents the polarization 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 as the porosity increases, the battery performance gradually increases. This is mainly because as the porosity increases, the reactive gas distribution is more uniform, and the space available for the foam to store water becomes larger, which increases the gas concentration and reduces the occurrence of flooding. Therefore, low humidity and high porosity are extremely important for metal foam fuel cells.

Claims (3)

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%.

Images