Degradation mechanisms in polymer electrolyte membrane fuel cells caused by freeze-cycles: Investigation using electrochemical impedance spectroscopy

Abstract

The performance of the polymer electrolyte membrane (PEM) fuel cells is sensitive to the exposure of these devices to subzero temperatures. In general, it is important to precondition the fuel cells prior to the shut-down preventing degradation after the start-up. Standard tests with conventional climatic chambers are nowadays costly and very time consuming. In this work, we introduce a method, which uses a simplified process with a PEM single-cell. The new design uses a Peltier-Element-Tempered (PET) single-cell with an active area size of 43.56 cm2. Now it is possible to achieve efficient and temperature controlled cold starts without a climate chamber or chiller plant. With the PET-controlled single cell, it was possible to do a series of complex accelerated freeze stress tests within the shortest time. To classify the performance change, polarization curves, cyclic voltammetry with the CV-CO-stripping method and Electrochemical Impedance Spectroscopy (EIS) at different current densities were performed. The measured impedance spectra were analyzed with a physical impedance model consisting of only 6 equivalent circuit elements. The charge-transfer resistance and the parameters of the Warburg diffusion element clearly reveal irreversible changes of the cathode during repeated freeze-cycles.