Methods to determine degradation in fuel cells

Polymer electrolyte fuel cells are a promising technology for converting the chemically bound energy of hydrogen into power. In order to establish fuel cells as a commercially viable product, the durability of membranes and electrodes in practical applications such as electric vehicles needs to be extended. The degradation mechanisms over lifetime are investigated by subjecting fuel cells to accelerated stress tests. Decomposition of the polymer electrolyte significantly affects the ionic conductivity and therefore the fuel cell performance. Cracks and tears form due to the thinning of the membrane, leading to reactant crossover and fluoride emissions. Electrochemical methods for characterizing degradation include polarization curves, electrochemical impedance spectroscopy and hydrogen diffusion current measurements. Local effects like flooding and dry-out of fuel cells are investigated using impedance spectroscopy in combination with total harmonic distortion analysis.