Abstract
Abstract Hydrogen is increasingly recognized as a clean, carbon-free energy carrier capable of supporting future sustainable energy systems. Water electrolysis provides a practical route for hydrogen generation, but its efficiency is determined by the catalytic performance of the hydrogen evolution reaction (HER). Transition metal phosphides (TMPs), particularly those derived from Fe, Co, Ni, and Mo, including their binary and multimetallic alloys, and alloys with other transition metals, have attracted significant attention due to their low overpotentials. Strong electrochemical stability and tunable catalytic activity. This review provides a comprehensive overview of the HER reaction mechanism, synthesis strategies, performance evaluation methods, and structural engineering approaches for TMP-based catalysts. Special emphasis is placed on alloyed phosphide systems incorporating these and other transition elements, which exhibit enhanced charge transfer, optimized hydrogen adsorption energies, and improved durability. The electrocatalytic behaviour of these phosphides under different phosphidation conditions is compared to reveal the structure–activity relationship. Despite considerable progress, several limitations persist, such as insufficient intrinsic activity, active-site instability, sluggish kinetics in alkaline media, and challenges in large-scale synthesis. To overcome these barriers, potential solutions and future research directions are proposed, including multi-metal alloy design, advanced in-situ/operando characterization, computationally guided catalyst screening and development. The advancements are expected to guide the development of high-performance Fe–, Co–, Ni–, and Mo–, based phosphide materials suitable for practical water splitting applications.