Electrochemical fabrication of multi-crystalline-amorphous heterogeneous single-atom electrocatalysts for alkaline oxygen evolution reaction

Constructing multiple nanosized heterogeneous structures with an in situ optimized coordination environment for dispersing and stabilizing noble metal single atoms (SAs) is a highly effective strategy for high-efficiency utilization of SAs and improving the electrocatalytic performances of the oxygen evolution reaction (OER). Herein, a multi-crystalline-amorphous heterogeneous composite (CoP2@CN–Ir(200)) composed of crystalline CoP2, amorphous CoOx and amorphous N-doped carbon was constructed for in situ loading of Ir SAs by cyclic voltammetry (CV) electrodeposition in an ionic liquid. By precisely controlling the electrodeposition cycles, the loading matrix of Ir SAs was simultaneously reconstructed and optimized. Some of the crystalline CoP2 is transformed into amorphous CoOx with activated high-valence Co; a coordination environment toward oxygenated species is built with more lattice oxygen and stronger adsorption ability of oxygen; the abundant heterointerfaces and the enhancement of the oxidation state disperse and stabilize Ir atoms in the form of OER-favorable high-valence Ir3+/Ir4+ by covalent Ir–O bonds (including Ir–O–Co bonds). As a result, abundant active sites with high intrinsic activity are exposed, and an accelerated charge transfer rate can be achieved, endowing CoP2@CN–Ir(200) with an outstanding electrocatalytic activity. Ultralow overpotentials of 189 and 300 mV at 10 and 100 mA cm−2, respectively, are achieved with a small Tafel slope of 36.9 mV dec−1, surpassing most reported remarkable Ir-related catalysts.