Reduction of Transition-Metal Columbite-Tantalite as a Highly Efficient Electrocatalyst for Water Splitting.

We successfully report a liquid-liquid chemical reduction and hydrothermal synthesis of a highly stable columbite-tantalite electrocatalyst with remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in acidic media. The reduced FeMnNbTaO (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm and 103.7 achieved at 20 mA cm current density in situ for the HER and OER, respectively. The electrocatalyst also exhibited low Tafel slopes of 104.97 mV/dec for the HER and 57.67 mV/dec for the OER, verifying their rapid catalytic kinetics. The electrolyzer maintained a cell voltage of 1.5 V and potential-time stability close to that of Pt/C and RuO. Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the FeMnTaNbO (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (Δ ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |ΔMn*| = 0.08 eV on the FeMnTaNbO (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|ΔPt*| ≈ 0.09 eV).