Carbon nanofiber catalysts containing high-entropy metal phosphides with low-content Ru for highly efficient hydrogen evolution reaction

High-entropy metal phosphide (HEMP) has considerable potential as an electrocatalyst owing to its beneficial properties, including high-entropy alloy synergy as well as the controllable structure and high conductivity of phosphides. Herein, electrospinning and in situ phosphating were employed to prepare three-dimensional (3D) networks of self-supporting HEMP nanofibers with varying degrees of phosphate content. Comprehensive characterizations via X-ray diffraction and X-ray photoelectron spectroscopy, as well as density functional theory calculations, demonstrate that the introduction of phosphorus (P) atoms to HEMP carbon nanofibers mediates their electronic structure, leads to lattice expansion, which in turn enhances their catalytic performance in the hydrogen evolution reaction (HER). Moreover, the formation of metal–P bonds weakens metal–metal interaction and decreases the free energy of hydrogen adsorption, contributing to the exceptional activity observed in the HEMP catalyst. Electrochemical measurements demonstrate that the HEMP-0.75 catalyst with an ultralow loading of 1.22 wt% ruthenium (Ru) exhibits the highest HER catalytic activity and stability in a 1 M KOH electrolyte, achieving a minimal overpotential of 26 mV at a current density of 10 mA·cm⁻² and Tafel slope of 50.9 mV·dec⁻¹.