Reversible degradation phenomenon in PEMWE cells

In proton exchange membrane water electrolysis (PEMWE) systems, voltage cycles dropping below a threshold are associated with reversible performance improvements, which remain poorly understood despite being documented in literature. The distinction between reversible and irreversible performance changes is crucial for accurate degradation assessments. One approach in literature to explain this behaviour is the oxidation and reduction of iridium. Iridium-based electrocatalyst activity and stability in PEMWE hinge on their oxidation state, influenced by the applied voltage. Yet, full-cell PEMWE dynamic performance remains under-explored, with a focus typically on stability rather than activity. This study systematically investigates reversible performance behaviour in PEMWE cells using Ir-black as an anodic catalyst. Results reveal a recovery effect when the low voltage level drops below 1.5 V, with further enhancements observed as the voltage decreases, even with a short holding time of 0.1 s. This reversible recovery is primarily driven by improved anode reaction kinetics, likely due to changing iridium oxidation states, and is supported by alignment between the experimental data and a dynamic model that links iridium oxidation/reduction processes to performance metrics. This model allows distinguishing between reversible and irreversible effects and enables the derivation of optimized operation schemes utilizing the recovery effect.

Tobias Krenz is a simulation and modelling engineer at Siemens Energy in the Transformation of Industry business area focusing on reducing energy consumption and carbon-dioxide emissions in industrial processes. He completed his PhD from Liebniz University Hannover in February 2025. He earned a degree from Berlin University of Applied Sciences in 2017 and a MSc from Technische Universität Darmstadt in 2020.

Alexander Rex is a PhD candidate at the Institute of Electric Power Systems at Leibniz University Hannover. He holds a degree in mechanical engineering from Technische Universität Braunschweig, an MEng from Tongji University, and an MSc from Karlsruhe Institute of Technology (KIT). He was a visiting scholar at Berkeley Lab from 2024 to 2025.