Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals for High‐Performance Electrocatalytic Overall Water‐Splitting

Abstract The synthesis of structurally ordered non‐noble intermetallic cobalt stannide (CoSn 2 ) nanocrystals and their utilization for high‐performance electrocatalytic overall water‐splitting is presented. The structurally and electronically beneficial properties of the tetragonal CoSn 2 exhibit a considerably low overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on fluorine‐doped tin oxide (FTO) and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation of Co under strongly alkaline conditions furnishes highly disordered amorphous active CoO x (H), the catalytically active structure for OER. The Co 0 atoms in the CoSn 2 act as active sites for HER and the presence of Sn provides efficient electrical conductivity. This intermetallic phase is a novel type of cost‐effective and competitive bifunctional electrocatalysts and predestinated for overall water‐splitting devices: A two‐electrode electrolyzer with CoSn 2 on NF delivers a cell voltage of merely 1.55 V at 10 mA cm −2 maintaining long‐term stability.