Fabrication and study of the synergistic effect of Janus Ni2P/Ni5P4 embedded in N-doped carbon as efficient electrocatalysts for hydrogen evolution reaction

Abstract

The integration of structural design and compositional modulation has been a hotspot for the optimization of electrocatalytic properties due to their synergistic effect. However, the details of this synergistic effect still lacks deep study. Herein, we fabricated an Ni₂P/Ni₅P₄ electrocatalyst with a Janus nanostructure embedded in N-doped carbon through a controllable phosphidation approach. The as-obtained hybrid catalyst realized an overpotential of 104 mV and Tafel slope of 38.5 mV dec⁻¹, which were smaller than that of the single Ni₂P and Ni₅P₄, at a current density of −10 mA cm⁻² in 0.5 M H₂SO₄ electrolyte. To reveal the reasons for the promotion of electrocatalytic properties, the synergistic effect was analyzed with the difference charge density (DCD), density of state (DOS), ΔG_H*, and strength of the internal electric field (IEF) on the interface between Ni₅P₄ and Ni₂P. The results indicated that the composite structures could optimize the ΔG_H* due to the change in the DOS instead of DCD. Further calculations indicated that the composite structure could modify the effective electric field, which is often overlooked and may be the reason for the change in the DOS. This study provides new insight for designing multi-component catalysts and deeply illuminating a part of the synergistic effect for high-efficiently electrocatalytic activities.