Unveiling the Role of Mo in MnCoMo Oxide for Efficient Hydrogen Production via Alkaline Seawater Electrolysis

Abstract Direct seawater electrolysis is a promising strategy for large-scale green hydrogen production, yet it remains hindered by the poor selectivity and durability of earth-abundant electrocatalysts under chloride-rich conditions. Here, we report a systematic investigation of the effect of molybdenum (Mo) content on the bifunctional electrocatalytic activity of hydrothermally synthesised MnCoMo oxide microrods grown on nickel foam (NF) substrates. Three compositions, MnCoMo_0.25, MnCoMo_0.5, and MnCoMo_0.75, were prepared by varying molybdenum concentration (0.25, 0.5, and 0.75 mmol, respectively). Electrochemically, MnCoMo_0.5 achieves the best oxygen evolution reaction (OER) performance in alkaline seawater, with a Tafel slope of 69 mV dec−1. MnCoMo_0.75 delivers superior hydrogen evolution reaction (HER) activity with a Tafel slope of 74 mV dec−1. Both electrodes demonstrate near-identical polarisation profiles across 1 M KOH, 1 M KOH + 0.5 M NaCl, and alkaline seawater electrolytes, demonstrating exceptional chloride tolerance. These results establish Mo loading as a critical tuning parameter for bifunctional activity and provide rational design principles for high-performance, earth-abundant seawater electrolysis catalysts.