crisis and environmental issue. [1] Electrochemical water electrolysis offers a promising and effective strategy to produce high-quality H 2 without carbon emission. [2] However, the sluggish kinetics of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been a huge challenge for water splitting, which has spurred researchers for exploiting high-efficiency electrocatalysts with reduced dynamic overpotentials. [3] AlthoughPt-based materials and Ru/Ir-based oxides are still known as the most efficient catalysts for HER and OER, they suffer from low abundance and high prices, leading to difficulties in the largescale commercial application. [4] In addition, the most obtained electrocatalysts are not capable of possessing both excellent HER and OER performance in a same electrolyte due to incompatibility of activity over different pH ranges. [5] Therefore, constructing non-noble metal bifunctional electrocatalysts with high performance and cost-effectiveness has become a hot spot for efficient overall water splitting.Recently, low-cost nickel chalcogenides, such as NiS, NiS 2 , and Ni 3 S 2 , have attracted enormous attention for electrolytic water splitting. [6] In particular, the Ni 3 S 2 electrocatalyst has been widely researched due to high conductivity and unique structure configuration, while the imprisoned HER/OER activity Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. Herein, a novel topdown 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.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.
