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Heteroatom-doping engineering has been recognized as an effective strategy to improve the activity and stability of electrocatalytic materials. Herein, we fabricated a bimetallic Mo/Mn codoped three-phase nickel sulfide on Ni foam, with Mo/Mn-NixSy/NF successfully synthesized via hydrothermal synthesis and calcination. In order to better explore the codoping effect of Mo/Mn, we also synthesised Ni3S2/NF, NiS@Ni0.96S/NF, Mo-Ni3S2/NF and Mn-NiS@Ni0.96S/NF and their electrocatalytic activities (HER, OER, and overall water splitting) were systematically investigated. As expected, Mo/Mn-NixSy/NF catalysts exhibited excellent catalytic activities and long-term durability. High electrochemical performance of Mo/Mn-NixSy/NF exceeded that of most reported non-precious metal catalysts and also benchmark RuO2, IrO2 and Pt/C. Moreover, in order to better understand the catalytic process, three possible mechanisms were further proposed to rationalize the enhanced electrocatalytic performance. Our work might broaden the avenue to construct efficient non-precious bifunctional catalysts and further develop large-scale electricity-to-hydrogen applications. [ABSTRACT FROM AUTHOR]

3D flower-like architecture (P, W)-MoO 2 /NF is employed as an efficient bifunctional catalyst for overall water splitting in 1.0 M KOH. • Flower-like architecture (P, W)-MoO 2 /NF is assembled on 3D nickel foam substrate. • Unique flower-like architecture is responsible for enhanced activity. • Synergistic electron interactions is beneficial to electrocatalytic properties. Due to the rapid consumption of fossil fuels and serious environmental pollution from nonrenewable energy, developing highly efficient, stable and earth-abundant bifunctional electrocatalysts for overall water splitting is thereby an urgent need but remains a significant challenge. Heteroatom doping is regarded as an effective tactic to facilitate electron interactions, and thereby enhance the electrocatalytic activity. In this work, (P, W)-codoped MoO 2 nanoflowers were successfully assembled on a nickel foam (NF) substrate (marked as (P, W)-MoO 2 /NF) by hydrothermal and phosphorization processes. The as-prepared catalyst (P, W)-MoO 2 /NF exhibits excellent catalytic activities with lower overpotentials of 308 mV and 89 mV to deliver 40 mA cm−2 for oxygen evolution reaction (OER) and 10 mA cm−2 for hydrogen evolution reaction (HER), respectively. More significantly, when directly assembled in the electrolyzer as a bifunctional electrocatalyst for overall water splitting, it only requires a cell voltage of 1.65 V to deliver a current density of 30 mA cm−2. The as-prepared catalyst (P, W)-MoO 2 /NF also displays splendid long-term stability over 20 h without a visible decrease in an alkaline solution. The blooming flower-like architecture can afford abundant active sites, and the doping of heteroatoms can tune the electronic transfer, which are both responsible for the enhancement in the electrocatalytic properties. This work provides a unique direction to the rational design and synthesis of highly efficient and stable non-noble metal molybdenum-based bifunctional electrocatalysts for overall water splitting. [ABSTRACT FROM AUTHOR]