The effect of the geometric area ratio between working and counter PEM electrodes for electrochemical hydrogen reactions

This work reports on the influence of the geometric area ratio between identical electrodes in MEA on their electrochemical performance. The difficulties in obtaining half-cell electrochemical data of MEAs motivated this research. The problem arises from the equality in geometric area of working electrode (WE) and counter electrode (CE), the thin distance between them (PEM thickness in the range 15–200 μm), the need of a reliable reference electrode, similar electrocatalyst loadings but different kinetics and electrocatalyst activities toward oxygen and hydrogen partial reactions. Thus, half-cell results obtained from MEAs may be influenced by the overloaded and, under certain conditions degrading CE. This is valid especially when the hydrogen oxidation (HOR) or evolution reaction (HER) is of interest and more kinetically limited reactions such as the oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) proceeds on the CE. The influence of the geometric area ratio (GAR) between CE and WE on their electrode performance was established. The approach used for reduction of the WE geometric area is via partially covering the electrode by a gas impermeable, electron conductive layer. The GAR required for avoiding CE influence on WE performance was established toward HOR and HER. All tests were performed under dead-end operation condition in the EasyTest Cell.