Interface Engineering of Hierarchical Branched Mo‐Doped Ni₃S₂/Ni<i>_x</i>P<i>_y</i> Hollow Heterostructure Nanorods for Efficient Overall Water Splitting

Abstract Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. Herein, a novel top‐down strategy to realize a hierarchical branched Mo‐doped sulfide/phosphide heterostructure (Mo‐Ni 3 S 2 /Ni x P y hollow nanorods), by partially phosphating Mo‐Ni 3 S 2 /NF flower clusters, is proposed. Benefitting from the optimized electronic structure configuration, hierarchical branched hollow nanorod structure, and abundant heterogeneous interfaces, the as‐obtained multisite Mo‐Ni 3 S 2 /Ni x P y /NF electrode has remarkable stability and bifunctional electrocatalytic activity in the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) in 1 m KOH solutions. It possesses an extremely low overpotential of 238 mV at the current density of 50 mA cm −2 for OER. Importantly, when assembled as anode and cathode simultaneously, it merely requires an ultralow cell voltage of 1.46 V to achieve the current density of 10 mA cm −2 , with excellent durability for over 72 h, outperforming most of the reported Ni‐based bifunctional materials. Density functional theory results further confirm that the doped heterostructure can synergistically optimize Gibbs free energies of H and O‐containing intermediates (OH*, O*, and OOH*) during HER and OER processes, thus accelerating the catalytic kinetics of electrochemical water splitting. This work demonstrates the importance of the rational combination of metal doping and interface engineering for advanced catalytic materials.