Constructing a NiCoP/FeP p–n heterojunction with built-in electric field regulation as an efficient alkaline hydrogen evolution electrode

Abstract

The development of high-performance alkaline hydrogen evolution reaction (HER) catalysts with robust stability and cost-efficiency is critical for advancing sustainable hydrogen production. While p–n heterojunction catalysts offer unique electronic modulation via built-in electric fields (BEFs), challenges such as insufficient charge redistribution and interfacial electron localization persist in oxide-based systems. Herein, the p–n heterojunction of homologous metal phosphides has been successfully constructed (NiCoP/FeP@CF). Benefiting from the electron transfer within the built-in electric field (BEF) of the p–n junction, the prepared NiCoP/FeP@CF heterojunction exhibited remarkable electrocatalytic activity and stability for water electrolysis-driven hydrogen evolution. Stability was achieved for over 60 h at a high current density of 200 mA cm⁻², and the catalyst showed excellent dynamic start–stop capabilities in cycling experiments. Characterization and theoretical simulations revealed that the electron transfer, driven by the difference in work functions, established an intrinsic BEF that balanced the Fermi levels within the NiCoP/FeP heterojunction. This induced the creation of electron accumulation and depletion zones on either side of the interface, optimizing the d-band center and the Gibbs free energy of hydrogen adsorption. As a result, the overall electrocatalytic activity of the electrode was significantly enhanced. This study provides valuable guidance for design of efficient electrocatalysts for water splitting using transition metal phosphides with p–n junctions.