Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in-operando approach

To evaluate the H2O2-tolerance of non-Pt oxygen reduction reaction (ORR) catalysts as well as investigate the H2O2-induced decay mechanism, the selection of an appropriate H2O2 concentration is a prerequisite. However, the concentration criterion is still unclear because of the lack of in-operando methods to determine the actual concentration of H2O2 in fuel cell catalyst layers. In this work, an electrochemical probe method was successfully established to in-operando monitor the H2O2 in non-Pt catalyst layers for the first time. The local concentration of H2O2 was revealed to reach 17 mmol/L, which is one order of magnitude higher than that under aqueous electrodes test conditions. Powered by the new knowledge, a concentration criterion of at least 17 mmol/L is suggested. This work fills in the large gap between aqueous electrode tests and the real fuel cell working conditions, and highlights the importance of in-operando monitoring methods.