| Proton Exchange Membrane Fuel Cell(PEMFC)is regarded as one of the most promising energy devices with high energy conversion rate,fast dynamic response,no noise and friendly enviro N ment.PEMFC has attracted much attention in the automotive field,but its application in the fields of underwater and aerospace is still little studied.PEMFC for underwater vehicle and aerospace applications generally needs to meet the following characteristics:confined space,pure hydrogen and oxygen;Maximize fuel efficiency and reduce gas emissions;Under the condition of pure oxygen,the degradation rate of the MEA film increases with the increase of the partial pressure of cathode oxygen,so the mechanical strength and chemical corrosion resistance of MEA are required to ensure the life of the fuel cell.In order to achieve the above objectives,the drainage strategy of hydrogen and oxygen fuel cells is generally through dead-ended and exhaust gas circulation.However,there is no systematic comparison of drainage strategies.In order to complete the test of dead-ended and circulation system,the test bench of dead-ended and circulation system is built.A single cell with a reaction area of 10cm~2and an8-piece stack were independently designed to test the basic performance of the hydrogen-oxygen fuel cell under different humidity,temperature and back pressure conditions,and to analyze the internal impedance of the cell with electrochemical analysis.Three different drainage strategies were tested for single cell and stack.For different drainage strategies,the influence of different operating conditions on the output performance of the cell was compared with the variation of voltage and high frequency impedance over time.The influence of different drainage strategies on the stack is mainly studied from the voltage output stability and voltage consistency of the stack.Through the above studies,the following conclusions can be drawn:For hydrogen-oxygen fuel cell,the output performance of fuel cell can be improved by increasing operating temperature and back pressure.In the low and medium current density region,increasing the humidity of the cell can improve the performance of fuel cell,but when the current density increases,the effect is not obvious.As the current density increases,the voltage consistency of the stack decreases,which is due to the combined influence of temperature and uneven gas distribution.Increasing the back pressure can increase the output performance of the stack,but has little effect on the voltage uniformity.The drainage strategy of dead-ended anode and cathode has the characteristics of simple system structure and small parasitic power loss.However,it will lead to a periodic voltage drop,so pulse purging is needed to restore the voltage.The increase of current density,no humidification of gas and the increase of purging duration will increase the purging interval.The drain strategy of dead-ended anode and cathode circulation neutralizes the advantages of double dead-ends and double circulation,with the cathode running steadily over long periods of time through a circulating pump.When the cell works under this drainage strategy,the cell voltage drop process has three stages:ohmic loss and concentration loss stage,quasi-equilibrium stage and water flooding stage.Increasing the pressure difference between anode and cathode,increasing the thickness of MEA and decreasing the working current density can make the output voltage of the cell more stable and increase the fuel efficiency.The double-circulation drainage strategy of anode and cathode can make the cell work stably for a long time,but it will also make the whole system more complicated due to the need for more parts.Among the three drainage strategies,the best voltage output stability and voltage consistency are the anode-cathode double cycle,dead-ended anode and cathode cycle drainage strategies,while the worst voltage consistency is the double dead-end drainage strategy,and some cell will be flooded. |
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