Regeneration of iron species for high and stable activity of nickel electrodes in the oxygen evolution reaction

Abstract

To enable green hydrogen production through alkaline water electrolysis, it is crucial to enhance the activity of nickel electrocatalysts towards the oxygen evolution reaction (OER), while preserving high stability. Here, we present a new and effective strategy to achieve this target through the introduction of short, periodical regeneration steps, complemented with the accurate tuning of traces of iron in the electrolyte. This strategy allowed retaining the enhanced activity brought about by the iron species adsorbed on the nickel electrode for the whole test duration (72 h) at an industrially relevant current density of 300 mA cm⁻² with a 1.0 M KOH electrolyte containing ca. 100 ppb of iron (mimicking a commercial electrolyte). Under the same conditions but without regeneration, a dramatic deactivation was observed after ca. 18 h. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) highlighted that such deactivation is correlated to the loss of iron species from the surface of the electrode. The regeneration steps help retain the iron species on the surface of the nickel electrode, thus granting the desired high OER activity and stability. We estimated that this regeneration strategy could lead to up to 18% energy saving compared to the current standard operating conditions of alkaline electrolysers.