Constructing built-in electric fields in 2D/2D Schottky heterojunctions for efficient alkaline seawater electrolysis

Abstract

Developing efficient and durable hydrogen evolution reaction (HER) electrocatalysts is critical for industrial and sustainable hydrogen production. Herein, a simple co-precipitation strategy is proposed to successfully construct catalysts with a Mott–Schottky heterojunction by coupling a transition-metal phosphate to the surface of stripped MXene thin-layer nanosheets (M₃(PO₄)₂@MXene, M = Co, Ni, and Fe). The Co₃(PO₄)₂@MXene with a unique tightly connected 2D/2D heterostructure and built-in electric field induces directional electron transfer at the interface, regulates the polarized structure of the active sites, and accelerates both mass and electron transport. Consequently, the optimized Co₃(PO₄)₂@MXene demonstrates outstanding HER performance, achieving low overpotentials of 46 and 58.6 mV at 10 mA cm⁻² in alkaline freshwater and seawater electrolytes, respectively. Moreover, the Co₃(PO₄)₂@MXene heterojunction catalyst maintains stable operation at a high current density of 500 mA cm⁻² for over 100 h in alkaline seawater electrolytes. More importantly, Co₃(PO₄)₂@MXene can offer a low potential of 1.71 V at 500 mA cm⁻² with stable operation for 50 h in a flow-type alkaline seawater electrolyser. This study provides a unique heterostructure in an electrocatalyst for an efficient HER and presents its potential application in seawater electrolysis.