Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
  • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
  • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04291—Arrangements for managing water in solid electrolyte fuel cell systems
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0082—Organic polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the invention relates to fuel cells which contain solid polymer membranes as the electrolyte, preferably hydrogen as the fuel gas and air or oxygen under low pressure as the oxidizing agent.
• the invention further relates to a method for simultaneously cooling the fuel cells and moistening the polymer electro membranes.
• Polymer electrolyte fuel cells as are commonly used to generate electrical current, contain one anode, one
• a plurality of fuel cells form a fuel cell stack, the individual fuel cells being separated from one another by bipolar plates acting as current collectors.
• a fuel gas for example hydrogen
• an oxidizing agent for example air or oxygen
• Anode and cathode each contain a catalyst layer in the areas in contact with the polymer electrolyte membrane.
• the fuel is oxidized to form cations and free electrons
• the cathode catalyst layer the oxidizing agent is reduced by taking up electrons.
• the cations migrate through the ion exchange membrane to the cathode and react with the reduced oxidizing agent, water being produced when hydrogen is used as the fuel gas and oxygen as the oxidizing agent.
• the reaction of fuel gas and oxidizing agent releases considerable amounts of heat, which have to be removed by cooling. Cooling was previously achieved by cooling channels in the bipolar plates, through which deionized water flowed. With this type of cooling there are enormous material problems, because typically about 50 to 300 bipolar plates are connected in series, so the cooling water electrically connects different potentials to each other. The result is material decomposition. Accordingly, only graphite or gold-plated metal can be used as the material for the bipolar plates.
• the object of the invention is to provide a polymer electrolyte fuel cell or a polymer electrolyte fuel cell stack, the polymer electrolyte membrane of a fuel cell always having the optimum moisture content during operation and at the same time ensuring adequate cooling.
• Fuel cell according to claim 1 the polymer electrolyte fuel cell stack according to claim 11, the method for cooling and humidifying a polymer electrolyte fuel cell according to claim 12 and the method according to claim 22.
• Polymer electrolyte membranes require a high water content in order to ensure optimal conductivity for H + ions.
• the water content must generally be maintained by supplying water, since otherwise the fuel and oxidant gas streams flowing through the cell dry out the membrane.
• Fig. 1 shows a preferred embodiment of a fuel cell according to the invention.
• Fig. 2 shows a circuit for measuring the impedance of a fuel cell.
• Fig. 3 shows the dependence of the conductivity of a Nafion 'membrane on the water content of the membrane.
• a polymer electrolyte fuel cell according to the invention is used
• Air or oxygen at low overpressure as an oxidizing agent as an oxidizing agent.
• An excess pressure of less than 2 bar is preferred, particularly preferably less than 0.5 bar.
• the required pressure difference can also be achieved by suction.
• Hydrogen is preferably used as the fuel gas, but the use of other fuel gases is also possible in principle.
• Nafion ® is preferably used as the polymer electrolyte membrane. Hydrogen is supplied to the individual fuel cells in a stack and distributed via gas channels in the anode area. At the same time air is supplied and distributed via gas channels in the cathode area. The hydrogen migrates to
• Anode catalyst layer and forms cations there, which migrate through the electrolyte, a proton exchange membrane, to the cathode.
• oxygen migrates to the cathode catalyst layer and is reduced there.
• water is formed as the reaction product.
• the water formed evaporates due to the heat of reaction, which results in a certain cooling.
• the cooling effect is not sufficient, on the other hand, the membrane becomes increasingly poor in moisture during the operation of the fuel cell.
• N (H 2 O) / N (SO 3 H) denotes the number of water molecules per sulfonic acid residue in the membrane.
• Polymer electrolyte membrane of a fuel cell therefore has the consequence that its internal resistance increases, that is to say its conductivity decreases.
• the conductivity of the membrane is extremely dependent on its water content. It is therefore essential for an efficient operation of a polymer electrolyte fuel cell that the polymer electrolyte membrane always has the optimum moisture corresponding to the respective working conditions (temperature, load, air ratio).
• the membrane is optimally moistened or whether water addition is required or what amount of water addition is required.
• the amount of water added can vary widely. It depends on the respective working conditions of the fuel cell, and in particular also depends on the type of cooling of the fuel cell. Fuel cells are often supplied for cooling, which, depending on the design of the fuel cells, also moistens the membrane to a certain extent. Then in the
• the conductivity of the membrane depends on its water content. However, the conductivity of the membrane cannot be measured directly while a fuel cell is in operation. According to the invention preferably the impedance of the fuel cell (amount of the impedance or particularly preferably real part of the impedance) is determined. Since the conductivity of the membrane is a constant, monotonous function of these variables, the amount of water required can also be regulated on the basis of the impedance.
• FIG. 2 A possible circuit for measuring the impedance of a fuel cell is shown in FIG. 2.
• Polymer electrolyte membrane of a fuel cell by determining the impedance is done by modulating the cell voltage with an alternating signal with a frequency of 1 to 20 kHz.
• the average moisture content of several membranes is suitably measured. The quotient from
• FIG. 2 represents the fuel cell and R L represents the load resistance.
• the voltage of the fuel cell is modulated by the alternating signal (approximately 1-20 kHz) from the alternating voltage source.
• the alternating voltage component U causes the fuel cell current to be superimposed with an alternating current I.
• AC voltage and alternating current is a measure of the impedance of the fuel cell and thus a measure of the moisture of the polymer electrolyte membrane, or of the amount of water required to be supplied.
• the amount of the impedance depends, apart from the conductivity of the membrane, on other parameters, namely the size of the catalyst surface that is in contact with the membrane, the ohmic resistance of the electrodes and the poisoning of the membrane by foreign ions. These sizes are subject to in the course of
• Service life of a fuel cell of some change where the deviations due to changes in the ohmic resistance of the electrodes and poisoning of the membrane by foreign ions are generally negligible.
• the amount of impedance that corresponds to the optimum membrane moisture under given operating conditions can vary. Therefore, the setpoint of the amount of the impedance to be maintained should be reset in the course of maintenance work.
• the new setpoint is determined by maximizing the performance of the fuel cell.
• the optimum setpoint can alternatively be readjusted by fuzzy logic or similar methods familiar to the person skilled in the art, in accordance with the changed conditions.
• a largely independent measure of the conductivity of the membrane is obtained from the catalyst surface (whose change is essentially responsible for the change in the setpoint value of the impedance). if, in addition to the magnitude of the impedance, its phase angle is also taken into account. If the real part of the impedance determined electronically from this is considered as a controlled variable, a single setpoint value can even be used over the entire service life of the fuel cell.
• the impedance (amount or real part) can be measured continuously or at regular intervals. If the conductance of the membrane or the membranes is calculated to be too low, water is supplied to the system, for example by opening water inlet valves electronically controlled in the usual way until the target value of the impedance is reached again.
• Membrane individually to determine, but average values for a plurality of cells of the stack or even for all cells of the stack to determine together and to adjust the required water addition accordingly.
• Water in liquid form is introduced immediately.
• the water can also be introduced directly into the gas channels for the fuel gas.
• the liquid water evaporates in the hot fuel cell and, due to the phase change taking place, causes efficient cooling of the cell. It also penetrates the polymer electrolyte membrane and keeps it moist.
• the membrane and more efficient cooling can be achieved if the required amount of water is added to the reaction gas streams in mixed form, i.e. as an aerosol.
• the water in the air Aerosol and possibly the water in fuel gas Aerosol contain water in the form of droplets of 2 to 20 ⁇ m in size, which ensure rapid evaporation or evaporation.
• the aerosol can be produced, for example, with the aid of ultrasonic atomizers or nozzles. The simplest and at the same time the least energy-intensive generation of the aerosol takes place by means of ultrasonic atomizers at frequencies of at least 100 kHz.
• a particularly advantageous embodiment of the invention is the design of the channels for receiving water in air aerosol or water-in-fuel gas aerosol, as shown in FIG. 1.
• each fuel cell is delimited by a bipolar plate 10, 6 on the anode and cathode sides.
• the anode-side bipolar plate is simultaneously the cathode-side bipolar plate of a neighboring cell and the cathode-side bipolar plate is simultaneously the anode-side bipolar plate of the other neighboring cell.
• the bipolar plate has corrugated sheet structure at least in a partial area, so it alternately has elevations and depressions.
• a surface of the bipolar plate 6 touches with its elevations 7 the cathode region 2 of the fuel cell, as a result of which the depressions 8 between the two adjacent elevations form channels 5 with the cathode region for receiving water in air aerosol.
• the surface of the bipolar plate 10 touches the anode region 3 of the cell, so that the depressions 12 located between two adjacent anode-side elevations 11 also form channels 9 with the anode region 3. These can be used to absorb water in fuel aerosol.
• hydrogen is fed in as the fuel gas through bores perpendicular to the plate surface.
• the hydrogen first enters channel 9, which is connected to the feed opening, and diffuses or flows from there into the adjacent porous anode region. From here the diffuses
• Hydrogen partly to the anode catalyst layer, partly in the Level of the anode area in further gas channels 9. Because of the excellent diffusion properties of hydrogen, the entire anode area is evenly supplied with hydrogen without any problems.
• cooling water is also to be fed in together with the fuel gas, it is generally more advantageous to choose the same type of supply as in the cathode region, that is to say to feed fuel and water into each individual channel 9. Because of the poor diffusion properties of water compared to hydrogen, little else would
• the construction has no separate cooling channels.
• a particular advantage is that the path of the aerosol through the channels 5 of the cell is a straight line.
• Corrugated sheet structure of the bipolar plate with straight gas paths makes it possible to minimize precipitation of the aerosol and to conduct the necessary volume flows with a small pressure drop.
• the "corrugated metal plate” is very simple and inexpensive to manufacture.
• Anode and cathode areas are each a suitable one
• Diffusion layers carrying catalyst are formed, which are arranged on the opposite sides of the polymer electrolyte membrane 4.
• Air seals 15, 15 'and hydrogen seals 16, 16' close the
• the walls of the gas channels 5 and / or the gas channels 9 can be covered with a hydrophilic absorbent layer, for example with felt.
• the hydrophilic, absorbent layer distributes the amount of water introduced evenly and holds it until it evaporates.
• the amount of water required to achieve optimal membrane moistening can, as stated above, be electronic
• Paths are determined and regulated.
• the amount of water introduced into the fuel cell has two functions: cooling the cell and moistening the membrane. However, only the setting of the suitable membrane moisture is taken into account to regulate the necessary amount of water. Depending on the
• Parameters temperature, load, air ratio etc. the optimal membrane moisture and thus the optimal conductivity of the membrane is determined experimentally.
• the water addition varies depending on the conductivity to be achieved.
• the cell temperature varies widely depending on the operating conditions. However, as long as sufficient water is introduced to ensure optimal membrane moisture, an adequate cooling effect is guaranteed.
• the reaction gas in particular the air
• the reaction gas can be passed through the cell stack several times. This is done by recycling the air / water mixture leaving the fuel cells or the fuel gas / water mixture leaving the fuel cells into the corresponding intake flow.
• the introduction of ion-free water in liquid form directly into the gas channels of the combustion air and / or of the fuel gas can simultaneously ensure that an optimum membrane moisture and thus an optimal conductance of the membrane and sufficient cooling of the fuel cell are maintained.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Fuel Cell (AREA)

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• 1997
  • 1997-04-10 EP EP97920648A patent/EP0985239A1/de not_active Withdrawn
  • 1997-04-10 JP JP54228198A patent/JP2001519080A/ja active Pending
  • 1997-04-10 WO PCT/EP1997/001792 patent/WO1998045889A1/de not_active Application Discontinuation
  • 1997-04-10 CA CA002286701A patent/CA2286701A1/en not_active Abandoned

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