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 Fe 0.79 Mn 0.21 Nb 0.16 Ta 0.84 O 6 (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm -2 and 103.7 achieved at 20 mA cm -2 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 2 . Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the Fe 0.75 Mn 0.25 Ta 1.875 Nb 0.125 O 6 (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (Δ G H* ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |Δ G Mn H *| = 0.08 eV on the Fe 0.75 Mn 0.25 Ta 1.875 Nb 0.125 O 6 (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|Δ G Pt H *| ≈ 0.09 eV).