Modulated electronic structure of atomic W-doped NiO/Cr₂S₃ nanotube heterostructure on nickel foam for enhanced overall water splitting

Critical for advancing hydrogen energy industrialization is the need to engineer durable and highly active non-precious electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER). In this study, we developed a novel approach to construct a vertically grown W-doped NiO/Cr₂S₃ nanotube heterostructure on nickel foam (referred to as tube W-NiO/Cr₂S₃/NF). This heterostructure serves as an efficient and bifunctional electrocatalyst for overall water splitting through a combination of electrodeposition and etching processes. Our systematic investigations revealed that W-doping effectively induces modifications in the electronic structure of NiO/Cr₂S₃, thereby boosting its intrinsic activities. Density functional theory reveals that catalytic activity for HER is influenced by the energy states of active valence dz² orbitals. After W-doping, the resulting antibonding state orbital's unique property, neither completely empty nor fully filled, leads to an ideal hydrogen adsorption energy. Consequently, tube W-NiO/Cr₂S₃/NF exhibits significantly enhanced performance for overall water splitting. As a bifunctional electrode, tube W-NiO/Cr₂S₃/NF demonstrates remarkable activity, achieving a cell voltage of 1.58 V at a current density of 10 mA cm⁻² for overall water splitting. Furthermore, it exhibits outstanding stability over 100 h in a 1.0 M KOH solution, outperforming commercial Pt-C and IrO₂ counterparts.