Spatial Mapping of Conductance and Electric Defects in Polymer Electrolyte Membrane Electrode Assemblies Using Lock‐In Thermography with AC Excitation

Abstract

The characterization of performance and losses of proton exchange membrane (PEM) and anion exchange membrane (AEM) electrolysis cells is typically carried out by electrochemical impedance spectroscopy and polarization curve measurements. With these common methods, lateral inhomogeneities, local degradation, or defects cannot be mapped. Lock‐in thermography (LIT) offers the possibility of mapping current flows and electrical losses. It has already been used successfully for many years in microelectronics and photovoltaics, among others. Conventional LIT with pulsed DC excitation does not work below the reversible voltage of water electrolysis. Therefore, high frequencies are used to generate the conductivity of the ion exchange membrane. Herein, for the first time, the method variable‐frequency AC excitation (VACE)‐LIT is presented. It combines aspects of electrochemical impedance spectroscopy with LIT and is applied to a PEM electrolysis membrane electrode assembly. It is shown that PEMs can exhibit strongly nonhomogeneous current densities, presumably resulting from contact resistances in the layer stack. In addition, local currents flowing at low frequencies indicate electronically conductive defects in the membrane.