The surface of metal boride tinted by oxygen evolution reaction for enhanced water electrolysis

Oxygen evolution reaction (OER) is a bottleneck half-reaction in many important energy conversion processes ( e.g. , water splitting), and one of the key issues lies to develop high-efficiency, cost-effective OER electrocatalysts. Rather than those popular extrinsic modulations of any catalysts with gradually degraded performance, we aim at the utilization of the intermediates offered from the undergoing OER as long-standing electrocatalysts. Herein, by inverted design, we extracted the bimetallic borides (FeCoB 2 )-derived intermediates metal borates in the OER, unlocking their potential as a self-functionalized highly active catalytic phase in-situ formed on the metal boride surface for continuing OER operation. Mechanistically, the surface metal atoms are oxidized to oxyhydroxides, and the surface metalloids (B) are further transformed to the corresponding oxoanions to form metal borates. Such OER self-produced electrocatalyst exhibits a small overpotential of 295 mV at 10 mA/cm 2 and its high catalytic activity lasts even after 200 h. Compared with FeCoB 2 , the catalytic activity of this electrochemically activated FeCoB 2 is ∼7 times higher. The in-situ formed metal borate is dominatingly responsible for the obtained high catalytic activity. Such unique OER-produced self-functionalization surfaces of metal borates afford to greatly reduce the energy barrier of the continuing OER, thereby accelerating the reaction process.