Textured NiSe₂ Film: Bifunctional Electrocatalyst for Full Water Splitting at Remarkably Low Overpotential with High...

Herein we have shown that electrodeposited NiSe₂ can be used as a bifunctional electrocatalyst under alkaline conditions to split water at very low potential by catalyzing both oxygen evolution and hydrogen evolution reactions at anode and cathode, respectively, achieving a very high electrolysis energy efficiency exceeding 80% at considerably high current densities (100 mA cm^-2). The OER catalytic activity as well as electrolysis energy efficiency surpasses any previously reported OER electrocatalyst in alkaline medium and energy efficiency of an electrolyzer using state-of-the-art Pt and RuO₂ as the HER and OER catalyst, respectively. Through detailed electrochemical and structural characterization, we have shown that the enhanced catalytic activity is attributed to directional growth of the electrodeposited film that exposes a Ni-rich lattice plane as the terminating plane, as well as increased covalency of the selenide lattice which decreases the Ni(II) to Ni(III) oxidation potential. Thereby, the high efficiency along with extended stability makes NiSe₂ as the most efficient water electrolyzer known to-date.