Achieving highly efficient pH-universal hydrogen evolution by Mott-Schottky heterojunction of Co2P/Co4N

Abstract

A vital step towards sustainable hydrogen production is to develop high-efficiency electrocatalysts for pH-universal hydrogen evolution reaction (HER). Modulation of the electronic structure of electrocatalysts by constructing Mott-Schottky heterojunction could be regarded as an effective strategy to promote the electrochemical performances. Herein, we report hybrid Mott-Schottky electrocatalyst composed of metallic Co4N and n-type semiconducting Co2P,fabricated via the hydrothermal method followed by the subsequent phosphating and nitriding treatment. Due to the Mott-Schottky effect, the self-driven charge carriers transfer occurs at the heterointerfaces of Co2P/Co4N, leading to a built-in electric field, accelerated charge transfer rate, and improved chemisorption free energies of the reaction intermediates, ultimately boosting the dissociation of water molecules. Therefore, the as-prepared Co2P/Co4N electrocatalyst exhibits outstanding pH-universal HER performance with extremely low overpotentials of 53, 19, and 32 mV at a current density of 10 mA cm−2 in 0.5 M H2SO4, 1 M phosphate buffer solution (PBS), and 1 M KOH electrolytes, respectively. Further, the electrocatalyst reveals low Tafel slopes of 38, 26, and 50 mV dec−1, which outperform those of the previously reported Co-based catalysts. Density functional theory (DFT) calculations clarify that the Schottky contact can regulate the adsorption energy of water, and the electronic structure at interface of the heterojunction weakens the hydrogen adsorption free energy (ΔGH*) of Co2P/Co4N to nearly zero, which is the reason for the addressed splendid HER performance.