Non‐Noble Bifunctional Amorphous Metal Boride Electrocatalysts for Selective Seawater Electrolysis

Abstract The global scarcity of freshwater resources has recently driven the need to explore abundant seawater as an alternative feedstock for hydrogen production by water‐splitting. This route comes with new challenges for the electrocatalyst, which has to withstand harsh saline water conditions with selectivity towards oxygen evolution over other competing reactions. Herein, a series of amorphous metal borides based on the iron triad metals (Co, Ni, and Fe), synthesized by a simple one‐step chemical reduction method, displayed excellent bifunctional activity for overall seawater splitting. Amongst the chosen catalysts, amorphous cobalt boride (Co−B) showed the best overpotential values of 182 mV for HER and 305 mV for OER, to achieve 10 mA/cm 2 , in alkaline simulated seawater. This superior activity was owed to the enrichment of the metal site with excess electrons (HER) and the in‐situ surface transformation (OER), as confirmed by various means. In alkaline simulated seawater, the overall cell voltage required to achieve 100 mA/cm 2 was 1.85 V for the Co−B catalyst when used in a 2‐electrode assembly. The Co−B catalyst showed negligible loss in activity even after 1000 cycles and 50 h potentiostatic tests, thus demonstrating its industrial viability. The selectivity of the catalyst was established with Faradaic efficiency of above 99 % for HER and 96 % for OER, with no detection of chloride products in the spent electrolyte. This study using the mono‐metallic boride catalysts will turn to be a precursor to exploit other complex metal boride systems as potential candidates for seawater electrolysis for large‐scale hydrogen production.