CN1684294A - Self heat radiation and self wetting fuel cell stack with high power density - Google Patents

Abstract

This invention relates to a self-radiation and a self-humidification fuel battery stack with high power density including a diversion bipolar plate, a proton exchange membrane electrode, a collecting plate and end plates, among which, multiple metal thin strips of high heat conductivity are set in the diversion bipolar plate and led out from both sides of the bipolar plate, metal fins for cooling are formed at both sides of the cell stack, one or multiple air or hydrogen diversion slots are opened between a pair of inlet and outlet holes of air or hydrogen diversion face of said bipolar plate, outlet of the hydrogen slot and the inlet of the air slot are at the same side of the bipolar plate, the inlet of the hydrogen slot and the outlet of the air slot are at the other side.

Description

A self-radiating and self-humidifying fuel cell stack with high power density

technical field

The invention relates to a fuel cell, in particular to a self-radiating and self-humidifying fuel cell stack with high power density.

Background technique

An electrochemical fuel cell is a device that converts hydrogen and oxidants into electrical energy and reaction products. The internal core component of the device is the membrane electrode (Membrane Electrode Assembly, referred to as MEA). The membrane electrode (MEA) is composed of a proton exchange membrane and two porous conductive materials, such as carbon paper, sandwiched between the two sides of the membrane. On the two boundary surfaces of the membrane and the carbon paper, there are even and finely dispersed catalysts for initiating electrochemical reactions, such as metal platinum catalysts. Conductive objects can be used on both sides of the membrane electrode to draw the electrons generated during the electrochemical reaction through an external circuit to form a current loop.

At the anode end of the membrane electrode, the fuel can permeate through the porous diffusion material (carbon paper), and an electrochemical reaction occurs on the surface of the catalyst, losing electrons and forming positive ions, which can migrate through the proton exchange membrane, Reach the cathode end of the other end of the membrane electrode. At the cathode end of the membrane electrode, a gas containing an oxidant (such as oxygen), such as air, penetrates through the porous diffusion material (carbon paper), and electrochemically reacts on the surface of the catalyst to obtain electrons to form negative ions. Anions formed at the cathode end react with positive ions migrating from the anode end to form reaction products.

In a proton exchange membrane fuel cell that uses hydrogen as fuel and air containing oxygen as the oxidant (or pure oxygen as the oxidant), the catalytic electrochemical reaction of fuel hydrogen in the anode region produces positive hydride ions (or protons). The proton exchange membrane facilitates the migration of positive hydride ions from the anode region to the cathode region. In addition, the proton exchange membrane separates the hydrogen-containing fuel gas stream from the oxygen-containing gas stream so that they do not mix with each other and cause an explosive reaction.

In the cathode area, oxygen gets electrons on the surface of the catalyst to form negative ions, and reacts with positive hydrogen ions migrated from the anode area to generate water as a reaction product. In a proton exchange membrane fuel cell using hydrogen and air (oxygen), the anode reaction and cathode reaction can be expressed by the following equation:

Anode reaction:

Cathode reaction:

In a typical proton exchange membrane fuel cell, the membrane electrode (MEA) is generally placed between two conductive plates, and the surface of each guide plate in contact with the membrane electrode is formed by die-casting, stamping or mechanical milling to form at least More than one diversion groove. These current guide plates can be made of metal or graphite. The fluid channels and flow guide grooves on these guide plates guide the fuel and oxidant into the anode area and the cathode area on both sides of the membrane electrode respectively. In the structure of a single proton exchange membrane fuel cell, there is only one membrane electrode, and the two sides of the membrane electrode are the deflectors of the anode fuel and the cathode oxidant respectively. These deflectors are not only used as current collectors, but also as mechanical supports on both sides of the membrane electrodes. The guide grooves on the deflectors are also used as passages for fuel and oxidant to enter the anode and cathode surfaces, and as a way to take away fuel cells during the operation of the fuel cell. Channels for the resulting water.

In order to increase the total power of the entire proton exchange membrane fuel cell, two or more single cells can usually be stacked in series to form a battery pack or connected in a tiled manner to form a battery pack. In direct-stacked and series-connected battery packs, there can be diversion grooves on both sides of a pole plate, one of which can be used as the anode diversion surface of one membrane electrode, and the other side can be used as the cathode of another adjacent membrane electrode. The diversion surface, this kind of plate is called a bipolar plate. A series of cells are connected together in a certain way to form a battery pack. The battery pack is usually fastened together by the front end plate, the rear end plate and the tie rods to form a whole.

A typical battery pack usually includes: (1) diversion inlet and diversion channel of fuel and oxidant gas, fuel (such as hydrogen, methanol or methanol, natural gas, hydrogen-rich gas obtained by reforming gasoline) and oxidant (mainly Oxygen or air) is evenly distributed into the diversion grooves of each anode and cathode surface; (2) the inlet and outlet of the cooling fluid (such as water) and the diversion channel, the cooling fluid is evenly distributed into the cooling channels in each battery pack, Absorb the heat generated by the electrochemical exothermic reaction of hydrogen and oxygen in the fuel cell and take it out of the battery pack for heat dissipation; (3) the outlet of the fuel and oxidant gas and the corresponding guide channel, when the fuel gas and oxidant gas are discharged, can Carry out the liquid and vapor state water generated in the fuel cell. Usually, the inlets and outlets of all fuels, oxidants, and cooling fluids are opened on one or both end plates of the fuel cell stack.

Proton exchange membrane fuel cells have the characteristics of starting at room temperature, high conversion efficiency, and zero pollution of products, so they have become the research focus of the current international community. Proton exchange membrane fuel cells are widely used. Large fuel cells can be used as power sources for submarines and automobiles; small fuel cells can be used as power sources for electric bicycles, notebook computers, digital cameras and other mobile electrical equipment.

The structure of a general fuel cell system mainly includes: a fuel cell stack, an air pump, an air humidifier, a hydrogen storage device, a hydrogen humidifier, a water pump, a water tank, and a radiator. Because the fuel cell will generate a lot of heat when it works at a high current density, generally speaking, it is necessary to use a cooling fluid, such as cooling water, which is forced to flow inside the fuel cell, driven by a water pump and then passed through an external radiator to take away the heat.

For small fuel cell stacks, it requires simple structure, compact structure and less auxiliary equipment. The proton exchange membrane fuel cell technology that adopts the above-mentioned general implementation has the following disadvantages:

1. The use of water as a cooling medium increases the heat capacity of the battery stack, slows down the temperature rise, and deteriorates operability at low temperatures.

2. Using water as the cooling medium requires a water pump to drive, which increases the power consumption of the entire fuel cell system and reduces the efficiency of the entire power generation system.

3. Using water as the cooling medium requires a water tank and a radiator, which increases the volume of the entire fuel cell system, and after the battery has been running for a period of time, water needs to be added to the water tank to supplement the water consumed by humidification.

In addition, there are two main types of humidification devices used in proton exchange membrane fuel cells: one is dry hydrogen or air and deionized water before entering the fuel cell, after direct collision in the humidification device, water molecules and hydrogen or air The molecules are uniformly mixed gaseous air and water molecules. After water vapor separation, when entering the fuel cell, it is hydrogen or air with a certain relative humidity; the other is dry hydrogen or air and deionized water before entering the fuel cell. The wet device is not in direct contact, but separated by a membrane that allows water molecules to pass through freely but does not allow gas molecules to pass through. When one side of the membrane flows through dry hydrogen or air and the other side of the membrane flows through deionized water Water molecules will automatically pass through the other side of the membrane from one side of the membrane, so that the air molecules and water molecules are mixed to reach a certain relative humidity of the air; this membrane can be a proton exchange membrane, such as DuPont's Nafion membrane, etc. Some other microporous membranes are also possible.

Adopting two kinds of humidifying device technologies in the existing fuel cell power generation system has the following technical defects for low-power fuel cells:

1. The use of the above two technologies requires an additional humidification device, which greatly increases the volume and weight of the fuel cell system.

2. Additional liquid pure water is required during the humidification process. The system generally requires a water tank, as well as a pure water circulation and replenishment system for humidification, which increases power consumption devices, such as water pumps, and fuel cell systems. volume and weight.

Contents of the invention

The object of the present invention is to provide a fuel cell stack with high power density, self-radiation and self-humidification with simple and reasonable structure, small volume, low cost and self-humidification in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions: a fuel cell stack with high power density self-radiation and self-humidification, including flow-guiding bipolar plates, proton exchange membrane electrodes, collector plates, end plates, the The two sides of the flow-guiding bipolar plate are the air-guiding surface and the hydrogen-guiding surface respectively. The flow-guiding bipolar plate and the proton exchange membrane electrode together form a single cell, and a series of single cells are stacked together with the current collector plate and the end plate Together to form a fuel cell stack, it is characterized in that a plurality of thin metal strips with high thermal conductivity are arranged inside the flow-guiding bipolar plate, and the thin metal strips are led out on both sides of the flow-guiding bipolar plate. After stacking the flow-guiding bipolar plate and the proton exchange membrane electrode, metal fins for cooling are formed on both sides of the entire fuel cell stack; One or more air diversion grooves are divided between the fluid holes, and one or more hydrogen diversion grooves are separated between a pair of fluid holes for entering and leaving hydrogen on the hydrogen diversion surface of the diversion bipolar plate, so The outlet of the hydrogen diversion tank and the inlet of the air diversion tank are on the same side of the diversion bipolar plate, and the inlet of the hydrogen diversion tank and the outlet of the air diversion tank are on the other side of the diversion bipolar plate.

The air inlet fluid hole divides into a plurality of air diversion grooves, and each of the plurality of air diversion grooves divides into a plurality of parallel branch air diversion grooves, and the branch air diversion grooves are collected at the other end A plurality of air guide grooves, and the plurality of air guide grooves then enter the fluid hole for air outlet.

The hydrogen inlet fluid hole is divided into a plurality of hydrogen diversion grooves, and each of the hydrogen diversion grooves is divided into a plurality of parallel hydrogen diversion grooves, and the hydrogen diversion grooves are collected at the other end A plurality of hydrogen diversion grooves, and the plurality of hydrogen diversion grooves then enter the fluid hole for hydrogen outlet.

The air diversion grooves on the diversion bipolar plate and the hydrogen diversion grooves are arranged in parallel.

The air guide groove has a depth of 0.3 mm to 1 mm and a width of 0.8 mm to 3 mm. The depth of the air diversion groove is preferably between 0.4 mm and 0.7 mm, and the width is preferably between 1 mm and 1.5 mm.

The hydrogen diversion groove has a depth of 0.3 mm to 1 mm and a width of 0.8 mm to 3 mm. The depth of the hydrogen diversion groove is preferably between 0.4 mm and 0.7 mm, and the width is preferably between 1 mm and 1.5 mm.

The production of the diversion bipolar plate of the present invention can be formed by molding, including air and hydrogen diversion grooves, graphite powder, thermosetting resin and many thin metal strips arranged in the graphite powder on the upper and lower layers of the mold.

The invention overcomes the technical defect of the proton exchange membrane fuel cell commonly implemented at present, and is a self-radiating and self-humidifying fuel cell. Therefore, it can greatly reduce the volume of the fuel cell, reduce the cost of equipment, and at the same time make the structure of the fuel cell more simple and reasonable, and the low-temperature startability of the fuel cell becomes better.

The fuel cell stack in the fuel cell of the present invention is flat and dissipates heat through the metal fins in the fuel cell stack. After starting, at low temperature, due to the small temperature difference between the temperature of the battery stack and the external environment, the heat dissipated is small, and the battery stack can heat up quickly; at high temperature, due to the increase in temperature difference, the heat dissipation also increases, and finally the battery can be stabilized Between 40°C and 60°C. In addition, the amount of air supplied to the battery is determined by measuring the current of the battery through the current sensor. Because the bipolar plate of the fuel cell of the present invention adopts the special design of air and hydrogen diversion grooves, the oxidant air and fuel hydrogen can not be additionally humidified, and the water produced by the reaction itself can be used to maintain the wet state of the membrane. Since the desorption of hydrogen in the hydrogen storage material needs to absorb heat, the hydrogen storage material bottle is placed near the metal fins so as to utilize the waste heat generated by the fuel cell. By adopting the method of air natural cooling, the fuel cell system can run stably, and the system structure is simple and the volume is small.

Description of drawings

Fig. 1 is a schematic structural diagram of the fuel cell system of the present invention;

Fig. 2 is a schematic diagram of the structure of the air surface of the diversion bipolar plate of the present invention;

Fig. 3 is a schematic diagram of the structure of the hydrogen surface of the diversion bipolar plate of the present invention;

Fig. 4 is the structural representation of proton exchange membrane electrode of the present invention;

Fig. 5 is a schematic structural diagram of the fuel cell stack of the present invention;

Fig. 6 is a time-varying curve of the output power of the fuel cell with a net output of 300W according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

As shown in Figures 2 to 4, the structure diagrams of the air surface of the diversion bipolar plate, the hydrogen surface of the diversion bipolar plate, and the membrane electrode are given, wherein the electrode 10 is a proton exchange membrane electrode, the air guide plate 11, the hydrogen gas Flow plate 12 is a bipolar plate, 14 is a sealing line, 15 is an air guide groove, and 16 is a hydrogen guide groove. Fig. 5 has provided the structural representation of fuel cell stack, and hydrogen deflector 12, air deflector 11 and proton exchange membrane electrode 10 form a single cell together, and a series of single cells are superimposed and then combined with collector plate 17, end plate 18 The fuel cell stack 13 is formed together; the air inlet 19, the air outlet 20, the hydrogen inlet 21, and the hydrogen outlet 22 are distributed on the end plate 18; the cooling air enters the fuel cell stack from top to bottom.

Fig. 1 shows the schematic diagram of the entire fuel cell system structure, wherein the hydrogen storage material tank 1 is a metal hydrogen storage tank, and there is a certain amount of hydrogen in the tank, which enters the fuel cell stack 3 after passing through the pressure reducing valve 2, and enters the fuel cell stack 3. The outlet is provided with a hydrogen flow control valve 4 . Air passes through the filter 5 and enters the fuel cell stack 3 through the air pump 6. There is a temperature sensor 7 and 9 at the air outlet of the fuel cell stack as a control circuit. The current sensor 8 provides electric energy and controls the operating state of the air pump 6 .

The whole battery system works like this: the hydrogen in the hydrogen storage material tank 1 passes through the pressure reducing valve 2 and then enters the hydrogen deflector of the fuel cell stack. The fuel cell system control circuit, the control circuit provides the electric energy generated by the fuel cell to the air pump, and the air pump sends air to the air deflector, and the system is in a standby state at this time. Then turn on the external load, measure the current through the current sensor, and then feed it back to the air pump to provide the appropriate air flow. Due to the adoption of a new flow field design, the fuel cell does not require external humidification, but maintains the humidity of the proton exchange membrane through the water generated by itself.

The following is a specific example of assembling a net output 300W integrated fuel cell system in the manner shown in Figure 1, wherein the effective area of the membrane electrode is 46cm ² , and the size of the diversion bipolar plate is 120mm×70mm. 40 cells were assembled into a fuel cell stack according to the method shown in Fig. 6 . The working temperature of the battery is 45°C, the total output voltage of the fuel cell stack is 24V, and the output current is 17A. Among them, the air pump consumes 60W, and the power consumed by other control circuits and actuators is very low, about 2W. Accompanying drawing 7 has given the battery output power change curve with time, it can be seen from this figure that the fuel cell system operating in this way can operate stably without external power supply.

Claims (6)

1. A fuel cell stack with high power density self-radiation and self-humidification, comprising a flow-guiding bipolar plate, a proton exchange membrane electrode, a current collector, and an end plate, and the two sides of the flow-guiding bipolar plate are respectively The air guide surface and the hydrogen guide air flow surface, the guide bipolar plate and the proton exchange membrane electrode together form a single cell, and a series of single cells are stacked together with the collector plate and the end plate to form a fuel cell stack, which is characterized in that, A plurality of thin metal strips with high thermal conductivity are arranged inside the flow-guiding bipolar plate, and the thin metal strips are led out on both sides of the flow-guiding bipolar plate, and are connected between the multiple flow-guiding bipolar plates, the proton exchange membrane After the electrodes are stacked, metal fins for cooling are formed on both sides of the entire fuel cell stack; one or more fluid holes are divided between a pair of fluid holes for air in and out of the air guide surface of the guide bipolar plate Air diversion groove, one or more hydrogen diversion grooves are divided between a pair of fluid holes for entering and leaving hydrogen on the hydrogen diversion surface of the diversion bipolar plate, and the outlet of the hydrogen diversion groove is connected to the air The inlet of the diversion groove is on the same side of the diversion bipolar plate, and the inlet of the hydrogen diversion groove and the outlet of the air diversion groove are on the other side of the diversion bipolar plate. 2. A fuel cell stack with high power density self-radiation and self-humidification according to claim 1, characterized in that, the fluid holes for the air intake are divided into a plurality of air guide grooves, and the plurality of Each of the air guide grooves is divided into a plurality of parallel branch air guide grooves, and the branch air guide grooves are brought together to a plurality of air guide grooves at the other end, and the multiple air guide grooves enter the outlet of the air. fluid hole. 3. A fuel cell stack with high power density self-radiation and self-humidification according to claim 1, characterized in that, the fluid holes for entering hydrogen are divided into a plurality of hydrogen guide grooves, and the plurality of hydrogen guide grooves Each of the hydrogen diversion grooves is separated into a plurality of parallel branch hydrogen diversion grooves, and the hydrogen diversion grooves are collected into multiple hydrogen diversion grooves at the other end, and the multiple hydrogen diversion grooves then enter the hydrogen outlet. fluid hole. 4. A fuel cell stack with high power density self-radiation and self-humidification according to claim 1, characterized in that, the air diversion groove on the diversion bipolar plate and the hydrogen diversion groove are in the form of parallel arrangement. 5. A fuel cell stack with high power density self-radiation and self-humidification according to claim 1, characterized in that, the depth of the air diversion groove is 0.3mm-1mm, and the width is 0.8mm- 3mm. 6. A fuel cell stack with high power density self-radiation and self-humidification according to claim 1, characterized in that, the depth of the hydrogen diversion groove is 0.3mm-1mm, and the width is 0.8mm- 3mm.

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