Investigation of the Degradation of the Membrane Electrode Assembly for a Proton Exchange Membrane Water Electrolyzer by Accelerated Stress Tests

Abstract

Proton exchange membrane (PEM) water electrolysis allows the production of green hydrogen using renewable but unstable energy sources such as wind or solar power. The lifetime assessment of a PEM water electrolyzer and its components require lengthy and costly testing, so there is a need for the development and application of accelerated stress-testing methods, which allow the accelerated investigation of degradation processes occurring under realistic operating conditions. In this study, the dynamic cycling and constant operation of the membrane electrode assembly of a PEM water electrolyzer at elevated voltages are considered as two methods of accelerated stress testing. The degradation depth, its distribution, and mechanisms are studied using electrochemical impedance spectroscopy, polarization curve breakdown into voltage losses components, and scanning electron microscopy. The greatest depth of degradation (up to 133 mV) is achieved during continuous operation of the membrane electrode assembly at elevated voltage, due to the anode porous transport layer (PTL) surface passivation and slow oxygen transport in its porous structure. The degradation depth of the membrane electrode assembly after dynamic cycling is found to be significantly lower (7–20 mV), and is related to degradation of the catalyst layer, with the decrease of mass transport losses being significantly responsible for the decrease in the overall degradation rate observed at high current densities. The influence of the anode catalyst loading reducing and the Ti-hydride protective coating on the surface of the anode PTL on the degradation of the PEM water electrolyzer is also considered. The use of a protective coating on the surface of the PTL provides the formation of a compact anode catalyst layer with a developed interface between the catalyst layer and PTL even at the reduced anode catalyst loading.