Amorphous FeCoNi-S as efficient bifunctional electrocatalysts for overall water splitting reaction

Developing bifunctional electrocatalysts for overall water splitting reaction is still highly desired but with large challenges. Herein, an amorphous FeCoNi-S electrocatalyst was developed using thioacetamide for the sulfuration of FeCoNi hydroxide during the hydrothermal process. The obtained catalyst exhibited an amorphous structure with hybrid bonds of metal-S bond and metal-O bonds in the catalyst system. The optimized catalyst showed a largely improved bifunctional catalytic ability to drive water splitting reaction in the alkaline electrolyte compared to the FeCoNi hydroxide. It required an overpotential of 280 mV and 80 mV (No-IR correction) to offer 10 mA/cm2 for water oxidation and reduction respectively; a low cell voltage of 1.55 V was required to reach 10 mA/cm2 for the water electrolysis with good stability for 12 h. Moreover, this catalyst system showed high catalytic stability, catalytic kinetics, and Faraday efficiency for water splitting reactions. Considering the very low intrinsic activity of FeCoNi hydroxide, the efficient bifunctional catalytic ability should result from the newly formed hybrid active sites of metallic metal-S species and the high valence state of metal oxide species. This work is effective in the bifunctional catalytic ability boosting for the transition metal materials by facile sulfuration in the hydrothermal approach.