CN2701083Y

CN2701083Y - A fuel cell with high power density self-dissipating heat and self-humidification

Info

Publication number: CN2701083Y
Application number: CNU2004200219129U
Authority: CN
Inventors: 董辉; 胡里清; 李丽
Original assignee: Shanghai Shen Li High Tech Co Ltd
Current assignee: Shanghai Shenli Technology Co Ltd
Priority date: 2004-04-14
Filing date: 2004-04-14
Publication date: 2005-05-18
Anticipated expiration: 2014-04-14

Abstract

The utility model relates to a fuel battery with high power density self-dissipating heat and self-humidification, comprising a diversion dual-polar plate, a proton exchanging membrane electrode, an afflux plate, and an end plate. The inner part of the diversion dual-polar plate is provided with a plurality of metallic thin strips which are provided with high-thermal conductivity are derived from the both sides of the diversion dual-polar plate; the both sides of the entire fuel battery pile form a metallic fin for cooling; one or a plurality of air or hydrogen gas diversion trenches are divided between a pair of fluid holes with the ingress and egress on the hydrogen diversion surface or the air diversion surface of the diversion dual-polar plate; the outlet of the hydrogen diversion trench and the inlet of the air diversion trench are at the same side of the diversion dual-polar plate, and the inlet of the hydrogen diversion trench and the outlet of the air diversion trench are at the other side of the diversion dual-polar plate. Compared with the prior art, the utility model with the self-humidification has the features of simple and reasonable structure, small size, low cost, etc.

Description

Self-heat dissipation and self-humidification type fuel cell stack with high power density

Technical Field

The present invention relates to fuel cells, and more particularly to a fuel cell stack with high power density and self-cooling and self-humidifying functions.

Background

An electrochemical fuel cell is a device capable of converting hydrogen and an oxidant into electrical energy and reaction products. The inner core component of the device is a Membrane Electrode (MEA), which is composed of a proton exchange Membrane and two porous conductive materials sandwiched between two surfaces of the Membrane, such as carbon paper. The membrane contains a uniform and finely dispersed catalyst, such as a platinum metal catalyst, for initiating an electrochemical reaction at the interface between the membrane and the carbon paper. The electrons generated in the electrochemical reaction process can be led out by conductive objects at two sides of the membrane electrode through an external circuit to form a current loop.

At the anode end of the membrane electrode, fuel can permeate through a porous diffusion material (carbon paper) and undergo electrochemical reaction on the surface of a catalyst to lose electrons to form positive ions, and the positive ions can pass through a proton exchange membrane through migration to reach the cathode end at the other end of the membrane electrode. At the cathode end of the membrane electrode, a gas containing an oxidant (e.g., oxygen), such as air, forms negative ions by permeating through a porous diffusion material (carbon paper) and electrochemically reacting on the surface of the catalyst to give electrons. The anions formed at the cathode end react with the positive ions transferred from the anode end to form reaction products.

In a pem fuel cell using hydrogen as the fuel and oxygen-containing air as the oxidant (or pure oxygen as the oxidant), the catalytic electrochemical reaction of the fuel hydrogen in the anode region produces hydrogen cations (or protons). The proton exchange membrane assists the migration of positive hydrogen 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 to cause explosive reactions.

In the cathode region, oxygen gains electrons on the catalyst surface, forming negative ions, which react with the hydrogen positive ions transported from the anode region to produce water as a reaction product. In a proton exchange membrane fuel cell using hydrogen, air (oxygen), the anode reaction and the cathode reaction can be expressed by the following equations:

and (3) anode reaction:

and (3) cathode reaction:

in a typical pem fuel cell, a Membrane Electrode (MEA) is generally placed between two conductive plates, and the surface of each guide plate in contact with the MEA is die-cast, stamped, or mechanically milled to form at least one or more channels. The flow guide polar plates can be polar plates made of metal materials or polar plates made of graphite materials. The fluid pore channels and the diversion trenches on the diversion polar plates respectively guide the fuel and the oxidant into the anode area and the cathode area on two sidesof the membrane electrode. In the structure of a single proton exchange membrane fuel cell, only one membrane electrode is present, and a guide plate of anode fuel and a guide plate of cathode oxidant are respectively arranged on two sides of the membrane electrode. The guide plates are used as current collector plates and mechanical supports at two sides of the membrane electrode, and the guide grooves on the guide plates are also used as channels for fuel and oxidant to enter the surfaces of the anode and the cathode and as channels for taking away water generated in the operation process of the fuel cell.

In order to increase the total power of the whole proton exchange membrane fuel cell, two or more single cells can be connected in series to form a battery pack in a straight-stacked manner or connected in a flat-laid manner to form a battery pack. In the direct-stacking and serial-type battery pack, two surfaces of one polar plate can be provided with flow guide grooves, wherein one surface can be used as an anode flow guide surface of one membrane electrode, and the other surface can be used as a cathode flow guide surface of another adjacent membrane electrode, and the polar plate is called a bipolar plate. A series of cells are connected together in a manner to form a battery pack. The battery pack is generally fastened together into one body by a front end plate, a rear end plate and a tie rod.

A typical battery pack generally includes: (1) the fuel (such as hydrogen, methanol or hydrogen-rich gas obtained by reforming methanol, natural gas and gasoline) and the oxidant (mainly oxygen or air) are uniformly distributed in the diversion trenches of the anode surface and the cathode surface; (2) the inlet and outlet of cooling fluid (such as water) and the flow guide channel uniformly distribute the cooling fluid into the cooling channels in each battery pack, and the heat generated by the electrochemical exothermic reaction of hydrogen and oxygen in the fuel cell is absorbed and taken out of the battery pack for heat dissipation; (3) the outlets of the fuel gas and the oxidant gas and the corresponding flow guide channels can carry out liquid and vapor water generated in the fuel cell when the fuel gas and the oxidant gas are discharged. Typically, all fuel, oxidant, and cooling fluid inlets and outlets are provided in one or both end plates of the fuel cell stack.

The proton exchange membrane fuel cell has the characteristics of room temperature start, high conversion efficiency, zero pollution of products and the like, thereby becoming the research focus of the current international society. The proton exchange membrane fuel cell has wide application, and the large fuel cell can be used as a power supply of submarines, automobiles and the like; the small fuel cell can be used as a power source of electric bicycles, notebook computers, digital cameras and other mobile electric equipment.

The structure of a general fuel cell system mainly includes: fuel cell stack, air pump, air humidifier, hydrogen storage device, hydrogen humidifier, water pump, water tank and radiator. Since the fuel cell generates a large amount of heat energy when operating at a high current density, a cooling fluid, such as cooling water, is generally required to flow forcibly inside the fuel cell, and the cooling fluid is driven by a water pump to take away the heat energy through an external radiator.

For a small fuel cell stack, it is required to have a simple and compact structure with few auxiliary devices. The proton exchange membrane fuel cell technology that has been generally pursued as described above has the following disadvantages:

1. the use of water as a cooling medium increases the thermal capacity of the stack, slows the rate of temperature rise, and degrades operability under low temperature conditions.

2. Water is used as a cooling medium, and a water pump is needed for driving, so that the power consumption of the whole fuel cell system is increased, and the efficiency of the whole power generation system is reduced.

3. The use of water as a cooling medium requires a water tank, a radiator, which adds bulk to the overall fuel cell system, and water needs to be added to the water tank after the cell has been in operation for a period of time to replenish the water consumed by humidification.

In addition, the humidifier applied to the proton exchange membrane fuel cell mainly has two types: one is that before dry hydrogen or air and deionized water enter into fuel cell, they are directly collided in the humidifying device to make water molecule and hydrogen or air molecule be gas air and water molecule which are uniformly mixed, after water-vapour separation, they are fed into fuel cell, and when they are hydrogen or air which can reach a certain relative humidity; the other is that the dry hydrogen or air and the deionized water are not directly contacted in the humidifying device before entering the fuel cell, but are separated by a layer of membrane which can allow water molecules to freely permeate but not allow gas molecules to permeate, when the dry hydrogen or air flows through one side of the membrane and the deionized water flows through the other side of the membrane, the water molecules automatically permeate through the other side of the membrane from one side of the membrane, so that the air molecules and the water molecules are mixed to reach air with certain relative humidity; the membrane may be a proton exchange membrane, such as a Nafion membrane from dupont, or some other microporous membrane.

The two humidification device technologies in the existing fuel cell power generation system have the following technical defects for the low-power fuel cell:

1. both of these techniques require additional humidification, which greatly increases the volume and weight of the fuel cell system.

2. In the process of humidification, extra liquid pure water is needed, a water tank is generally needed in the system, and a pure water circulating and supplementing system for humidification is needed, so that power consumption devices such as a water pump and the like are added, and the volume and the weight of the fuel cell system are also increased.

SUMMERY OF THE UTILITY MODEL

The present invention aims at providing a fuel cell stack with high power density, self-heat dissipation and self-humidification, which has simple and reasonable structure, small volume, low cost and self-humidification, and can overcome the defects of the prior art.

The purpose of the utility model can be realized through the following technical scheme: a fuel cell stack with high power density, self-heat dissipation and self-humidification comprises a flow guide bipolar plate, a proton exchange membrane electrode, a current collecting plate and an end plate, wherein the two surfaces of the flow guide bipolar plate are respectively an air flow guide surface and a hydrogen flow guide surface; one or more air guide grooves are arranged between a pair of air inlet and outlet fluid holes of the air guide surface of the guide bipolar plate, one or more hydrogen guide grooves are arranged between a pair of hydrogen inlet and outlet fluid holes of the hydrogen guide surface of the guide bipolar plate, the outlet of the hydrogen guide groove and the inlet of the air guide groove are arranged on the same side of the guide bipolar plate, and the inlet of the hydrogen guide groove and the outlet of the air guide groove are arranged on the other side of the guide bipolar plate.

The fluid hole of the inlet air is divided into a plurality of air diversion grooves, the plurality of air diversion grooves are respectively divided into a plurality of parallel branch air diversion grooves, the branch air diversion grooves are converged into a plurality of air diversion grooves at the other end, and the plurality of air diversion grooves enter the fluid hole of the outlet air.

The hydrogen inlet flow hole is divided into a plurality of hydrogen guide grooves, the plurality of hydrogen guide grooves are divided into a plurality of parallel branch hydrogen guide grooves, the branch hydrogen guide grooves are converged into a plurality of hydrogen guide grooves at the other end, and the plurality of hydrogen guide grooves enter the hydrogen outlet flow hole.

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

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

The depth of the hydrogen guide groove is 0.3 mm-1 mm, and the width of the hydrogen guide groove is 0.8 mm-3 mm. The depth of the hydrogen guide groove is preferably between 0.4mm and 0.7mm, and the width is preferably between 1mm and 1.5 mm.

The utility model discloses water conservancy diversion bipolar plate's production can utilize the mould pressing to form, lower floor is provided with air, hydrogen guiding gutter including the mould, graphite powder, thermosetting resin and the many metal thin strips of setting in graphite powder.

The utility model overcomes the technical defects of the proton exchange membrane fuel cell which is generally implemented at present, and is a self-heat dissipation and self-humidification fuel cell. Therefore, the volume of the fuel cell can be greatly reduced, the equipment cost is reduced, the structure of the fuel cell becomes simpler and more reasonable, and the low-temperature starting performance of the fuel cell becomes better.

The fuel cell stack in the fuel cell of the utility model is flat, and the heat dissipation is carried out through the metal fins in the fuel cell stack. After starting, the temperature difference between the temperature of the cell stack and the external environment is small at low temperature, so that the heat dissipation is small, and the cell stack can be rapidly heated; at high temperature, the temperature difference is increased, the heat dissipation capacity is increased, and finally the battery can be stabilized between 40 ℃ and 60 ℃. The amount of air supplied to the battery is determined by measuring the current of the battery by means of a current sensor. The bipolar plate of the fuel cell of the utility model adopts the special design of the air and hydrogen diversion trenches, so the oxidant air and the fuel hydrogen can not be additionally humidified, and the water generated by the reaction is adopted to maintain the wet state of the membrane. Since hydrogen desorption in the hydrogen storage material requires heat absorption, the hydrogen storage material can be bottled in the vicinity of the metal fins to facilitate utilization of waste heat generated by the fuel cell. By adopting the natural air cooling method, the fuel cell system can stably run, and has simple structure and small volume.

Drawings

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

FIG. 2 is a schematic view of the structure of the air surface of the flow-guiding bipolar plate of the present invention;

FIG. 3 is a schematic diagram of the structure of the hydrogen surface of the flow-guiding bipolar plate of the present invention;

FIG. 4 is a schematic view of the proton exchange membrane electrode structure of the present invention;

FIG. 5 is a schematic diagram of a fuel cell stack according to the present invention;

fig. 6 is a graph showing the change of the net output 300W of the fuel cell with time according to the present invention.

Detailed Description

The present invention will be further explained with reference to the accompanying drawings.

As shown in fig. 2 to 4, schematic structural diagrams of the air surface, the hydrogen surface and the membrane electrode of the flow guide bipolar plate are shown, in which the electrode 10 is a proton exchange membrane electrode, the air guide plate 11 and the hydrogen guide plate 12 are bipolar plates, 14 is a seal line, 15 is an air guide groove, and 16 is a hydrogen guide groove. Fig. 5 shows a schematic structural diagram of a fuel cell stack, wherein a hydrogen guide plate 12, an air guide plate 11 and a proton exchange membrane electrode 10 form a single cell, and a series of single cells are stacked and form a fuel cell stack 13 together with a collector plate 17 and an end plate 18; an air inlet 19, an air outlet 20, a hydrogen inlet 21 and a 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 a schematic structural diagram of the whole fuel cell system, wherein, the hydrogen storage material tank 1 is a metal hydrogen storage tank, a certain amount of hydrogen gas is in the tank, and enters the fuel cell stack 3 after passing through the pressure reducing valve 2, and a hydrogen flow control valve 4 is arranged at the outlet of the fuel cell stack 3. Air enters the fuel cell stack 3 through the filter 5 by the air pump 6, atemperature sensor 7 and a temperature sensor 9 are arranged at the air outlet of the fuel cell stack and are used as a control circuit, and the electric energy generated by the fuel cell is used for providing electric energy for the air pump 6, the temperature sensor 7 and the current sensor 8 and controlling the running state of the air pump 6.

The entire battery system is operated as follows: hydrogen in the hydrogen storage material tank 1 enters a hydrogen guide plate of the fuel cell stack after passing through the pressure reducing valve 2, the voltage of the fuel cell stack rises at this time, a control circuit of the whole fuel cell system is started after a certain value is reached, the control circuit supplies electric energy generated by the fuel cell to an air pump, the air pump sends air to the air guide plate, and the system is in a standby state at this time. The external load is then switched on, the current is measured by the current sensor and then fed back to the air pump to provide the appropriate air flow. Because of adopting a novel flow field design, the fuel cell does not need to be additionally humidified, but maintains the humidification of the proton exchange membrane through the water generated by the fuel cell.

The following is an example of assembling a net output 300W integrated fuel cell system in the manner of FIG. 1, in which the membrane electrode has an effective area of 46cm²The size of the flow guide bipolar plate is 120mm multiplied by 70 mm. The 40 cells were assembled into a fuel cell stack according to the method of figure 6. The working temperature of the cell is 45 ℃, the total output voltage of the fuel cell stack is 24V, and the output current is 17A. In which the air pump consumes 60W, and the power consumed by other control circuits and actuators is as low as about 2W. Fig. 7 shows the cell output power as a function of time, from which it can be seen that a fuel cell system operated in this manner can be operated stably without an external power source.

Claims

1. A fuel cell stack with high power density, self-heat dissipation and self-humidification comprises a flow guide bipolar plate, a proton exchange membrane electrode, a current collecting plate and an end plate, wherein the two surfaces of the flow guide bipolar plate are respectively an air flow guide surface and a hydrogen flow guide surface; one or more air guide grooves are arranged between a pair of air inlet and outlet fluid holes of the air guide surface of the guide bipolar plate, one or more hydrogen guide grooves are arranged between a pair of hydrogen inlet and outlet fluid holes of the hydrogen guide surface of the guide bipolar plate, the outlet of the hydrogen guide groove and the inlet of the air guide groove are arranged on the same side of the guide bipolar plate, and the inlet of the hydrogen guide groove and the outlet of the air guide groove are arranged on the other side of the guide bipolar plate.

2. The fuel cell stack of claim 1, wherein the air inlet opening is divided into a plurality of air channels, each of the plurality of air channels is divided into a plurality of parallel air channels, the air channels converge to the other end of the plurality of air channels, and the air channels enter the air outlet opening.

3. The fuel cell stack according to claim 1, wherein the hydrogen inlet flow hole is divided into a plurality of hydrogen channels, each of the hydrogen channels is divided into a plurality of parallel branch hydrogen channels, the branch hydrogen channels converge to the other end of the hydrogen channels, and the branch hydrogen channels enter the hydrogen outlet flow hole.

4. The fuel cell stack of claim 1, wherein the air channels and the hydrogen channels of the bipolar plate are arranged in parallel.

5. The fuel cell stack of claim 1, wherein the air channels have a depth of 0.3mm to 1mm and a width of 0.8mm to 3 mm.

6. The fuel cell stack of claim 1, wherein the hydrogen guiding grooves have a depth of 0.3mm to 1mm and a width of 0.8mm to 3 mm.