Teaching experiment design for dynamic performance testing of high-temperature proton exchange membrane fuel cells
[Objective]To improve hydrogen utilization,high-temperature proton exchange membrane fuel cells(HPEMFCs)are usually operated in dead-end anode or anode recirculation mode.However,this usually leads to the accumulation of impurity gases such as water vapor,which gradually degrade the fuel cell performance and generally needs to be solved by anode purging.Different current density loads and purging conditions have an important impact on the dynamic performance of fuel cells,and measuring the dynamic characteristics of fuel cells under different current densities and purging conditions can improve the accuracy of the fuel cell model,which is conducive to the optimization of the overall control strategy of the stack and the enhancement of the stack's operating performance.[Methods]In this paper,a thermostat is used to control the operating temperature of an HPEMFC;an electronic load is used to control the current density load of the fuel cell,and a solenoid valve controlled by a microcontroller is used to control the opening and closing of the anode line of the fuel cell.The experiments are mainly to measure the forward and reverse scans of the polarization curves of the HPEMFC under different current density loads,as well as the transient voltages in the forward and reverse directions under different current densities in anode flow mode and anode purging mode.[Results]The experimental results of the dynamic performance test of theHPEMFC show that(1)the two curves of the polarization curve forward sweep measurement and back sweep measurement do not completely overlap,but there is a hysteresis phenomenon,and the voltage difference under the low current density interval is higher than the voltage difference under the high current density interval.(2)On the rising edge of the current load step,a transient voltage downstroke is observed,while on the falling edge,an overshoot is observed.Subsequently,the transient voltage undergoes a fast recovery process and a slow recovery phase thereafter.At the same current density,the maximum value of the transient voltage during the current load rise is lower than the minimum value of the transient voltage during the current load fall.(3)The peak and transient voltage in flow mode are very similar for all current steps,and the peak-to-peak curve in the fixed purging mode shows better performance.[Conclusions]The experimental results show that changes in the humidity level of the high-temperature proton exchange membrane will directly affect the conductivity of the membrane.The internal resistance is first high and then low when the current increases and is the opposite when the current decreases.The internal resistance returns to the expected value when the fuel cell reaches a steady state.Therefore,the membrane impedance decreases in the forward sweep and increases in the backward sweep.The peak voltage of an HPEMFC in dead-end mode can be predicted by appropriately correcting the transient voltage in flow mode.Introducing the above exploratory experiments in undergraduate experimental teaching,guiding students to analyze and discuss the experimental results,and achieving growth of scientific research and teaching have vigorously improved students'comprehensive scientific research quality.
high-temperature proton exchange membrane fuel cellsdynamic performance testingintegration of science and educationintegration of science and reality
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