CoHPi Nanoflakes for Enhanced Oxygen Evolution Reaction.

Electrochemical splitting of water to produce hydrogen and oxygen is an important process for many energy storage and conversion devices. Developing efficient, robust, low-cost, and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is therefore of great importance. Herein, we report a novel method to prepare two-dimensional cobalt hydrogen phosphate (CoHPi) through chemical conversion of α-Co(OH)2 precursor at room temperature. The CoHPi nanoflakes with the thickness of 3 nm contain HPO4 2- anions, which have been demonstrated to serve as a proton acceptor in proton-coupled electron-transfer (PCET) process of OER. Due to their ultrathin structure and the PCET merit of anions, the CoHPi nanoflakes show enhanced OER activity as well as excellent stability in prolonged OER operation. Through further mechanism study, the observed performances can be ascribed to enriched active sites, surface superhydrophilicity, and rapid electron/proton and mass transfers.