Exploring and understanding the internal voltage losses through catalyst layers in proton exchange membrane water electrolysis devices

[Display omitted] •Internal voltage losses in PEM water electrolysis cell can be deconvoluted.•The electrical resistance of catalyst layers in PEMWE cells is in-situ measured.•The electrical resistances of the anode catalyst layers changed dynamically during operation.•The sensing methodology could be applied to other energy storage/conversion systems. Proton exchange membrane water electrolysis (PEMWE) technology has been regarded as one of the most promising ways to fulfill a sustainable energy system when coupled with renewable energies. Understanding the working mechanisms and losses in PEMWE devices is critical for achieving the desired performance and durability that targets wide commercial applications. This work demonstrates a novel four-wire sensing technique for acquiring the internal voltage losses in an operating PEMWE cell, which deconvolutes the total cell voltage into five parts. Most importantly, the ohmic resistances on anode and cathode catalyst layers are in-situ and operando measured. The two catalyst layer resistances show completely different values and trends under the same operating conditions, which is mainly due to the electrical conductivity difference between the two layers. The ohmic resistance of the anode catalyst shows an exponential decay with current density, which is in accordance with previously published visualization results, and shows a dependency on temperature; while the ohmic resistance of the cathode catalyst layer is a constant and not related to operating conditions. With the adoption of the technique, a phenomenon in which the ohmic resistance of the anode catalyst changes dynamically during the cell testing is captured and recorded for the first time. These findings provide very valuable data and results for understanding the catalyst layer working mechanisms, and also help to optimize the future catalyst layer. The four-wire sensing technique developed in this study is a promising tool for diagnosis, analysis, and optimization not only for PEMWE devices, but also potentially for other energy storage and conversion devices.