Comparative analysis of electrocatalytic performance for HER and OER in alkaline and acidic water splitting

Electrochemical water splitting produces hydrogen without direct CO2 emissions, but the economics depend entirely on catalyst performance. This paper benchmarks overpotential and Tafel slope data from recent experimental literature for six catalyst families, namely transition metal alloys, MOF-derived electrodes, g-C3N4 and rGO composites, biochar-based carbons, and noble-metal oxides, across alkaline and acidic electrolytes. In alkaline media, earth-abundant materials now reach HER overpotentials of 67 mV and OER overpotentials of 151 mV. Acidic OER remains the harder problem, as iridium and ruthenium still dominate in PEMWE, though non-noble HER catalysts have improved considerably. Tafel slopes, where reported, are used to identify rate-determining steps rather than treated as secondary metrics. Gaps in characterisation, particularly missing Tafel data for biochar and alloy systems, are flagged for future work.