Overlooked Impact of Electrolyte Purity on Benchmarking Cathodes in Alkaline Water Electrolysis

A catalyst’s performance is inherently linked to its operating environment. Therefore, evaluation under appropriate experimental conditions is essential for accurate results. This work underscores the impact of electrolyte purity on the performance of nickel-based catalysts in alkaline water electrolysis, a factor well recognized in oxygen evolution research but often neglected in hydrogen evolution studies. We show that trace impurities in laboratory-grade KOH can significantly distort the apparent performance of nickel cathodes during hydrogen evolution at industrially relevant conditions (1000 mA/cm 2 in 6 M KOH). These effects persist even when no visible deposits are present. Fundamental studies of nickel-based catalysts should use only high-purity-grade KOH. However, for industrial settings where impurities are likely unavoidable, testing conditions should be adjusted accordingly to ensure meaningful results.