Sharma, S. K. / Wu, C. / Malone, N. / Titheridge, L. J. / Zhao, C. / Gupta, P. / Idriss, H. /  Kennedy, J. V. / Jovic, V. / Marshall, A. T. (2025)

International Journal of Hydrogen Energy, 2025, 102, 1461-1479

Abstract

Ruthenium (Ru-) based electrocatalysts have historically shown the highest activity for the oxygen evolution reaction in green H2 production by PEM-based water electrolysis. However, their instability under industrially relevant operating conditions makes the considerably more expensive and scarcer Ir/IrO2-based electrocatalysts the materials of choice for industrial use – an important technical bottleneck that contributes to the high levelized-cost of green H2. Despite decades of research, meeting the ‘Key Performance Indicators’ of industrial systems with Ru/RuO2-based electrocatalysts is not yet possible, with an in-depth understanding of the engineering strategies and their induced effects still at an early stage. Framing our review from the perspective of a PEM water electrolyser, and the demands that the operating environment puts on the core components, we focus on the state-of-the-art Ru-based electrocatalysts and the physicochemical properties that were used to optimise performance (decrease overpotential and prolong stability). Further, we highlight that due to the intrinsic heterogeneity of the electrocatalysts, an improvement to a certain figure of merit, e.g., stability or activity, is a complex combination of various interlinked factors. We find that most research efforts focus on electrocatalyst preparation via trial-and-error methods and evaluation at low currents densities in short durations. We discuss the obstacles such an approach presents on standardization of results in individual studies, across the community and on the extraction of industrially relevant information. Also, our discussion highlights potential failure mechanisms and development strategies that may maximise the likelihood of success in an applied scenario. Our review underscores the urgent need for electrocatalyst synthesis and testing under more standardized (and closer to applied) conditions if the goal is to develop an industrially relevant material.

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