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In the study of earth-abundant oxygen evolution reaction (OER) electrocatalysts, cation-doping is an extensively used strategy to boost the catalytic performance, whereas anion-doping is a promising yet premature approach that...

Transition metal borides (TMBs) are a class of important but less well-explored electrocatalytic materials for water splitting. The lack of an advanced methodology to synthesize complex nanostructured TMBs with tunable surface properties is a major obstacle to the exploration of the full potential of TMBs for electrocatalytic applications. Here, we report the facile fabrication of a cobalt foam (CF)-supported hierarchical nanostructured Co−Mo−B/CoMoO 4−x composite using a hydrothermal method, followed by annealing and NaBH 4 reduction treatments. Our study found that NaBH 4 reduction of CoMoO 4 resulted in the concurrent formation of amorphous Co−Mo−B and an O-vacancy-rich CoMoO 4−x substrate, which cooperatively catalyzed the hydrogen evolution reaction (HER) in an alkaline electrolyte. The hierarchical nanoporous structure derived from the dehydration and partial reduction reactions of the CoMoO 4 • nH 2 O precursor could offer ample accessible active sites, as well as interconnected channels for rapid mass transfer. In addition, the in situ growth of electrically conductive Co−Mo−B nanoparticles on the defective structured CoMoO 4−x substrate imparted the electrocatalyst with good electrical conductivity. As a result, the Co−Mo−B/CoMoO 4−x /CF catalyst showed impressively high activity and outstanding stability for the alkaline HER, outperforming most reported TMB electrocatalysts. For instance, it required an overpotential of 55 mV to afford 10 mA•cm −2 and showed a fluctuation of only ±8 mV in a 100 h constant-current test at 100 mA•cm −2 .

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