Experimental study on dynamic voltage uniformity of a 2-kW air-cooled PEMFC

Abstract

The existing kW-class air-cooled proton exchange membrane fuel cells (PEMFC) usually control the exhaust valve and fan according to the manufacturer’s recommendations of the purge interval and the optimum temperature, respectively. However, the single-cell voltage and its uniformity under dynamic working conditions are not considered. Nonetheless, single-cell voltage and its uniformity are important factors that reflect and affect the performance and lifetime of the stack. Therefore, it is necessary to investigate the dynamic uniformity of the single-cell voltages under conventional control mode. Based on a self-built 2-kW air-cooled PEMFC test platform, this paper investigated the voltage responses and the single cell dynamic voltage uniformity for PEMFC under dynamic working conditions. For the step loading and unloading conditions, it was observed that the larger the step amplitude, the greater the voltage overshoot or undershoot, the greater the volatility of the single-cell voltage, and the longer the time to restore stability. In particular, large step loading at small currents and large step unloading at high currents can seriously damage single-cell voltages and their uniformity. In addition, large step unloading at high currents has a greater negative impact on the cell voltage than large step loading. For a continuous loading or unloading situation with a constant slope, dynamic variable loading experiments with different frequencies and amplitudes were designed to reach a specified current from different initial currents. It was observed that with an increase in the loading and unloading amplitude and frequency, the uniformity of single-cell voltage becomes worse. However, the effect of ramp loading is greater than that of ramp unloading. Finally, based on these experimental results, dynamic variable loading suggestions involving the voltage uniformity were proposed, which have certain guiding significance and reference value for the practical applications of kW-class air-cooled PEMFC.