Porous metal bipolar plate fuel cell

Abstract

The invention belongs to an internal humidifying fuel cell, and particularly relates to a porous metal bipolar plate fuel cell. The pressure and the flow speed between reaction gas and circulating water on the two sides of the porous metal bipolar plate are controlled through a gas supply auxiliary system, a circulating water auxiliary system and the like, so that the circulating water forms two-way permeation in micropores of the porous metal bipolar plate, and dynamic balance of gas humidification and discharge of redundant generated water is achieved; the porous metal bipolar plate adopted by the invention realizes dual effects of humidification and drainage in the battery, a humidification device is omitted, humidification is uniform, drainage is timely, dynamic response of power output is fast, the service life of the battery is effectively prolonged, the system volume and the system energy consumption are reduced, in addition, the physical property of the porous metal plate is superior to that of a porous graphite plate, and the service life of the battery is prolonged. When hydrogen and oxygen are used as reaction gases, the fuel cell can realize totally-closed operation, and can be applied to deep sea diving, high-altitude low-temperature flight, space navigation, violent vibration and other extreme environments to provide power.

Description

Technical Field

[0001] The present invention belongs to an internally humidified fuel cell, and particularly relates to a porous metal bipolar plate fuel cell. Background Art

[0002] At present, the known structure and working process of a proton exchange membrane fuel cell: A fuel cell is formed by stacking a number of fuel cell units. Each fuel cell unit consists of a membrane electrode and a bipolar plate. The membrane electrode is composed of a proton exchange membrane, a catalytic layer, and a porous gas diffusion layer. On both sides of the membrane electrode, bipolar plates processed with gas and liquid fluid channels made of graphite plates or metal plates are pressed and stacked together. As an important component of the fuel cell, the bipolar plate functions mainly in gas distribution, heat dissipation, electrical conduction, water and heat management, supporting the MEA, and structural sealing, etc., enabling the reaction gases - hydrogen and air (or oxygen) to be respectively transported and evenly distributed on both sides of the membrane electrode. During operation, hydrogen is used as the fuel gas and air (or oxygen) as the oxidant, and a chemical reaction occurs under the action of the catalyst of the membrane electrode, generating water, heat, and electrical energy. During the reaction process of the fuel cell, the proton exchange membrane can only conduct hydrogen protons when it is wet, forming an electric current, and water is generated on the cathode side. Under the water concentration gradient difference on both sides of the membrane electrode, water will migrate from the cathode side to the anode side. If the membrane electrode is overly dry, its proton conduction efficiency will decrease sharply, and the battery output power will decrease. At the same time, in addition to self-humidification, if there is too much water content on the surface of the membrane electrode, in the diffusion layer, and in the bipolar plate, the channels for the reaction gases will be blocked. If the excess water cannot be discharged in time, the battery cannot work. Therefore, to maintain the stable operation of the fuel cell, the water volume balance inside the battery must be ensured, neither too little nor too much. To ensure that the proton exchange membrane contains an appropriate amount of moisture, a humidification link needs to be set in the fuel cell system. The humidification methods include self-humidification, external humidification, and internal humidification: Self-humidification refers to making the membrane electrode itself have the ability of humidification and moisture retention by reducing the thickness of the proton membrane, adjusting the hydrophilicity and hydrophobicity of the membrane electrode, or changing the gas flow direction, using the water generated by the battery; External humidification is to heat and humidify the reaction gas before it enters the fuel cell, such as bubbling humidification, enthalpy wheel humidification, spraying humidification, etc., which not only increases power consumption and cost, but also increases volume and weight. Internal humidification generally means that the gas is directly humidified inside the fuel cell. One common method is to add a "false cell" without a catalytic layer inside the battery as a humidification section, and directly transfer the moisture in the outlet hot and humid tail gas through the proton membrane to the dry gas at the inlet for humidification. Another method is to add a membrane humidification cavity inside the battery, that is, a permeable membrane is used in the cavity to separate the reaction gas from the battery cooling water. Under the action of the concentration difference and pressure difference, water evaporates through the membrane into the reaction gas. However, these two methods increase the complexity of the battery structure.

[0003] In addition to the above humidification methods, there is also a method of humidification by using a porous graphite material to make bipolar plates. For example, the method mentioned by UTC in patents US5503944 and US5700595. Utilizing the porous characteristics formed during the preparation of the graphite plate, a bipolar plate of the battery made of a porous graphite plate has a circulating water flow channel and a gas flow channel designed on both sides respectively. By adjusting the pressure between the circulating water and the cathode and anode reaction gases, liquid water permeates bidirectionally from both sides of the porous graphite bipolar plate, humidifying the dry gas and discharging the excess generated water, achieving the purpose of two-way balance adjustment. However, this method has the following deficiencies:

[0004] 1. The porous graphite bipolar plate has a small density and poor mechanical properties, and the battery volume is relatively large, restricting the power / volume density of the battery. Its fuel cell engine system cannot be widely used due to the limited installation space size;

[0005] 2. The pores and pore diameters of the porous graphite plate are randomly formed during the preparation of the blank, and its effective porosity, pore diameter and distribution cannot be accurately controlled. Therefore, the uniformity of its humidification is inconsistent, increasing the complexity of pressure control and indirectly affecting the uniformity and stability of the battery;

[0006] 3. The material properties of the porous graphite plate are worse than those of metal materials and are not suitable for use in high-frequency vibration, severe shock, large pressure difference, extreme low temperature or vacuum environments;

[0007] 4. The flow field of the porous graphite as the bipolar plate of the battery is processed by numerical control engraving, with high costs and is not suitable for mass production on a large scale.

[0008] In view of the above problems, the present invention proposes a porous metal plate as the bipolar plate of a fuel cell, including the principle, material and flow field structure to solve the above problems. Summary of the Invention

[0009] The present invention proposes to use a porous metal plate instead of a porous graphite plate to prepare a bipolar plate of a fuel cell. Among various porous metal materials, the titanium foam metal plate has the following physical characteristics:

[0010] 1. The material of the bipolar plate of the fuel cell needs to have the physical characteristics of electrical conductivity, thermal conductivity and corrosion resistance.

[0011] Foamed metal is a metal material containing foam pores. It not only retains the characteristics of metal materials such as weldability, electrical conductivity, and ductility, but also has the functional properties of porous materials such as energy absorption and vibration damping, air and water permeability, and filtration. Foamed metals mainly include foamed aluminum, foamed magnesium, foamed copper, foamed nickel, foamed steel, foamed titanium, etc. Among them, foamed titanium is a porous material made from industrial high-purity titanium powder through sieving, static pressure forming, and then high-temperature vacuum sintering. Its parameters such as porosity, pore size, shape, and distribution are determined by parameters such as the diameter of raw material particles, static pressure forming process, and sintering temperature. The surface of the plate can be processed into a groove shape, and the parameters such as the size and spacing of the grooves are achieved through the mold used in material forming according to the size requirements of the flow field of the battery bipolar plate. It not only has excellent mechanical properties and can be machined mechanically such as cutting and welding, but also has electrical and thermal conductivity characteristics.

[0012] 2. To achieve the effects of humidification and drainage in the bipolar plate of an internally humidified fuel cell, it is necessary to have the characteristics of water passage and gas blockage:

[0013] Taking the foamed titanium metal plate as an example, its porous characteristics are formed during the production process. Using its plate to prepare the bipolar plate of a fuel cell can make the gas and water on both sides of the bipolar plate form the effects of gas blockage and water passage through flow rate, pressure gradient, and capillary action, that is: the liquid water in the circulating water chamber penetrates through the micropores of the porous titanium plate to the gas flow field on the other side to humidify the dry gas. At the same time, the liquid water generated during the operation of the battery penetrates to the circulating water flow field on the other side of the bipolar plate through the velocity, pressure gradient, and capillary action of the fluid, playing a drainage effect and realizing the two-way dynamic regulation of liquid water.

[0014] According to the requirements of the gas flow field and the circulating water flow field of the fuel cell, the present invention uses metal powder as the raw material, which is made into a porous material through sieving, static pressure forming, and high-temperature vacuum sintering. Its parameters such as porosity, pore size, shape, and distribution are determined by parameters such as the diameter of raw material particles, static pressure forming process, and sintering temperature. The parameters such as the groove shape, size, and spacing of the plate are determined by the mold used in the material forming process. Through mold forming or roll forming, the grooves required for the bipolar plate flow field are obtained, and then the porous metal plate with grooves is machined mechanically into a bipolar plate. The porous metal plate has electrical conductivity, thermal conductivity, corrosion resistance characteristics, and metal processing characteristics. Then it is stacked with the membrane electrode assembly into a stack, and the pressure and flow rate of the reaction gas and the circulating water on both sides of the porous metal bipolar plate are controlled respectively through auxiliary systems such as gas supply and circulating water, so that the circulating water forms two-way penetration in the micropores of the porous titanium bipolar plate to achieve the dynamic balance of humidifying the gas and discharging the excess generated water.

[0015] The present invention has the following essential differences from the methods mentioned in US Patents US5503944 and US5700595 of UTC Corporation in the United States:

[0016] 1. Different materials: The porous metal plate - titanium foam plate described in the present invention belongs to a kind of metal material, while the graphite material used by UTC Company in the patent is a non-metal material.

[0017] 2. The bipolar plate made of the porous metal plate - titanium foam plate described in the present invention can be mass-produced through a mold, while the bipolar plate made of porous graphite can only be produced by numerical control machining, with high cost and low efficiency.

[0018] 3. Different material properties: The porous metal plate - titanium foam plate adopted in the present invention has excellent metal processing properties, while the porous graphite plate does not have metal processing properties.

[0019] 4. The porous metal plate - titanium foam plate described in the present invention has hydrophilicity by itself, while the porous graphite plate does not have hydrophilicity.

[0020] 5. The physical properties of the porous metal plate - titanium foam plate described in the present invention are superior to those of the porous graphite plate, and it can be used under extreme low temperature, high pressure difference, and vacuum conditions.

[0021] Principle of the technical solution of the present invention:

[0022] According to Bernoulli's equation, the ideal fluid flowing steadily in a pipe has three forms of energy: pressure energy, potential energy, and kinetic energy. Under certain conditions, the three forms of energy in the flow field can be converted into each other, but their sum remains unchanged, that is: kinetic energy + gravitational potential energy + pressure potential energy = constant.

[0023] Based on the above law, when the reaction gas - air and circulating water flow from both sides of the porous metal bipolar plate respectively, the water permeation direction depends on the magnitude of the static pressure of the reaction gas and circulating water on both sides of the porous metal bipolar plate; the amount of water permeation is related to parameters such as the pressure difference of the fluid, capillary force, and the pore diameter, porosity, and thickness of the porous metal plate material. The specific process is described in detail as follows:

[0024] 1. Humidification process: When air and circulating water enter the flow channels of the porous metal bipolar plate respectively, through the design of the flow field and the control of the auxiliary system, when the air velocity is greater than the circulating water velocity and the pressure on the air side is lower than the pressure on the circulating water side, a pressure difference is generated, driving the circulating water to permeate through the micropores of the metal flow field plate to the air side, evaporating and humidifying in the air, and then permeating to the membrane electrode through capillary action and concentration difference for humidification.

[0025] 2. Drainage process: During the operation of the battery, water is generated in the cathode catalyst layer and permeates through the diffusion layer. It gradually grows from small droplets and converges into a liquid film attached to the surface of the porous metal bipolar plate. Its flow rate is close to zero, much smaller than the flow rate of the circulating water on the other side of the bipolar plate, and the pressure of the liquid water on the cathode side is greater than that on the circulating water side. Driven by the pressure difference, the liquid water on the cathode side penetrates through the micropores of the porous metal plate to the circulating water side, discharging the excessive accumulated water on the cathode side and ensuring the smooth flow of the gas flow channel of the battery. Brief Description of the Drawings:

[0026] Attached Figure 1 is a schematic diagram of the principle of the present invention.

[0027] Attached Figure 2 is a cross-sectional view of a specific embodiment of the present invention.

[0028] Attached Figure 3 is an axonometric view of a specific embodiment of the present invention.

[0029] Attached Figure 4 is a view of the single-sided grooved porous metal plate of a specific embodiment of the present invention.

[0030] Attached Figure 5 is a three-view drawing of the circulating water flow field of a specific embodiment of the present invention.

[0031] Attached Figure 6 is a three-dimensional assembly drawing of a specific embodiment of the present invention.

[0032] Attached Figure 1 is a schematic diagram of the principle of the present invention. As shown in the figure, air 1 and circulating water 4 are isolated by a porous metal bipolar plate 3. When the flow rates, static pressures, concentration gradients, and capillary actions of air 1 and circulating water 4 are involved, liquid water - circulating water and generated water perform two-way dynamic permeation between the air-side flow field and the circulating water flow field of the bipolar plate through the pores 2 of the porous metal bipolar plate 3 to achieve the humidification of the gas and the discharge of the generated water.

[0033] Humidification process: When dry air 1 and circulating water 4 enter the flow channels on both sides of the porous metal bipolar plate respectively, the micropores 2 inside the porous metal bipolar plate 3 are wetted by the circulating water, generating a bubble point pressure P_bubble due to the surface tension of water. When referring to the atmospheric pressure, when the air flow rate is greater than the circulating water flow rate, ν_air > ν_circulating water, the static pressure on the air side is less than that on the circulating water side, p_air < p_circulating water. When p_air < p_circulating water + P_bubble, driven by the pressure difference between the gas and the liquid, the circulating water penetrates through the micropores 2 of the porous metal bipolar plate to the air side and evaporates and humidifies in the air-side flow channel;

[0034] Drainage process: During the operation of the fuel cell, the liquid water generated in the cathode catalyst layer permeates through the diffusion layer, gradually expands from small droplets, and converges into a liquid water film attached to the air-side surface of the porous metal bipolar plate. Its flow rate is close to zero, much smaller than the flow rate of the circulating water on the other side of the porous metal bipolar plate, i.e., νair-side water < νcirculating water. The static pressure on the air side is greater than that on the circulating water side, i.e., pair-side water > pcirculating water. Driven by the pressure difference, the liquid water film on the air side is permeated through the micropores 2 to the circulating water side, thereby discharging the excessive generated water on the air side.

[0035] In the above process, the water permeation direction depends on the magnitudes of the static pressures of the reaction gas side and the circulating water side on both sides of the porous metal bipolar plate; the water permeation quantity is related to parameters such as the pressure difference of the fluid, capillary force, and the pore diameter, porosity, and thickness of the porous metal plate material. The flow rate and pressure of the fluids on both sides of the porous metal bipolar plate are adjusted by methods such as the proportional valve of the auxiliary system and the speed regulation of the water pump motor; the fluids on both sides refer to the reaction gas and the circulating water, not only the air and the circulating water, but also the hydrogen and the circulating water. Specific implementation manner:

[0036] To enable those skilled in the art to more clearly understand the technical principle, scheme structure, and technical advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] Att Figure 2 It is a view of the porous metal plate with grooves on one side - the material adopted in the specific embodiment of the present invention. One side of the porous metal plate is a plane, and the other side is processed by a forming mold into a shape with grooves 1 and ridges 2 alternating and parallel. The structure is simple, easy to form, suitable for batch production, and has a low cost.

[0038] Att Figure 3 It is a cross-sectional view of a single cell - the specific embodiment of the present invention. As shown in the figure, the single cell is composed of a cathode plate 1, a circulating water flow field plate 2, a seal 3, a metal frame 4, an anode plate 5, an anode diffusion layer 6, a proton membrane 7, and a cathode diffusion layer 8. Among them, the cathode plate 1, the circulating water flow field plate 2, and the anode plate 5 all adopt the porous metal plate material with grooves on one side. The circulating water flow field plate is composed of two single-sided grooved plates, with their planes pasted back to back and inserted into the metal frame 4, and then pressed together with the cathode plate 1 and the anode plate 5 through the seal 3 to form a circulating water flow field.

[0039] Att Figure 4 It is an axonometric view of a single cell - the specific embodiment of the present invention. As shown in the figure, the groove 1 of the cathode plate 2 is the inlet and outlet air (oxygen) flow channel; the groove 6 of the anode plate 5 is the inlet and outlet hydrogen flow channel; the metal frame sandwiched between the cathode plate and the anode plate is processed with circulating water inlet and outlet flow channels 3, respectively forming three relatively independent cavities for air (oxygen), hydrogen, and circulating water, and then forming a battery unit after being pressed together with the diffusion layer and the membrane electrode.

[0040] Attached Figure 5 Figure 5 is the three - view drawing of the circulating water flow field of a single - cell, which is a specific embodiment of the present invention. As shown in the figure, the diagonals of the metal frame 2 are respectively processed with the inlet 1 and the outlet 5 of the circulating water. The flow field plate 4, which is composed of two single - sided grooved plates with the grooves facing outwards and the planes pasted back - to - back, is inserted into the metal frame 2. Moreover, a certain width of space is left at the left and right ends of the circulating water flow field plate as the diffuser chamber of the circulating water to facilitate the uniform distribution of the circulating water. In addition, sealing components are arranged on both side surfaces of the metal frame, and the thickness L1 of the metal frame plus the seal is greater than the thickness L2 of the flow field plate 4, and the thickness L2 of the flow field plate 4 is greater than the thickness L3 of the metal frame 2, that is, the relationship L1>L2>L3 is satisfied.

[0041] Attached Figure 6 Figure 6 is the three - dimensional assembly drawing of a specific embodiment of the present invention. As shown in the figure, multiple single - cells are stacked together to form a battery stack 5. Air inlet hoods 1, air outlet hoods 3 and water inlet hoods 8, water outlet hoods 3 of the circulating water are respectively arranged along the diagonals on the upper and lower surfaces of the battery stack 5; hydrogen inlet hoods 6 and outlet hoods 10 are respectively arranged on the left and right side surfaces of the battery stack 5. In addition, inlet and outlet connectors 2, 4, 7, etc. are processed on the side surfaces of each gas hood.

[0042] In summary, compared with the prior art, the bipolar plate of the present invention uses a porous metal plate, which realizes the dual functions of humidification and drainage, eliminates the humidification device. It not only has uniform humidification, timely drainage, fast dynamic response of power output, effectively extends the service life of the battery, but also reduces the system volume and system energy consumption. In addition, the physical properties of the porous metal plate are superior to those of the porous graphite plate. When hydrogen and oxygen are used as reaction gases, the fuel cell can operate in a fully enclosed manner and can be applied to provide power in extreme environments such as deep - sea diving, high - altitude low - temperature flight, and space aerospace.

Claims

1. A porous metal bipolar plate fuel cell, comprising a fuel cell composed of a porous metal bipolar plate with grooves, characterized in that: The bipolar plate of the fuel cell is made of a porous metal plate with grooves. Under the regulation of the pressure and flow rate of the fluids on both sides of the porous metal bipolar plate by the auxiliary system, the liquid water realizes the two-way water permeability function through the pores inside the porous metal bipolar plate.

2. The porous metal plate with grooves according to claim 1, characterized in that: The multi-porous material made from metal powder through screening, static pressure forming, and high-temperature vacuum sintering has its parameters such as porosity, pore diameter, shape, and distribution determined by parameters such as the diameter of the raw material particles, the static pressure forming process, and the sintering temperature.

3. The porous metal plate with grooves according to claim 1, characterized in that: The parameters such as the groove shape, size, and spacing of the plate are realized through the mold used in the material forming according to the size requirements of the flow field of the fuel cell bipolar plate.

4. The porous metal plate according to claim 1, wherein: The porous metal plate has the characteristics of electrical conductivity, thermal conductivity, corrosion resistance, and metal processing.

5. The bidirectional water permeability function according to claim 1, characterized in that: The water permeation direction depends on the combined action of the static pressure on the reaction gas side and the static pressure on the circulating water side on both sides of the porous metal bipolar plate and the capillary force; the water permeation amount is related to the pressure difference of the fluid, as well as parameters such as the pore diameter, porosity, and thickness of the porous metal plate material.

6. The pressure and flow rate adjustment of fluids on both sides of a porous metal bipolar plate by an auxiliary system according to claim 1, characterized in that: The fluids on both sides refer to the reaction gas and the circulating water, where the reaction gas refers to hydrogen and air (oxygen); the regulation of pressure and flow rate is achieved through the proportional valve of the auxiliary system and the regulation of the pump motor speed.

Images