Vanadium-Modulated Molybdenum/Nickel-Based Multi-Heterostructures finely tailoring d-Band centers for electrocatalytic water splitting.

Finely tailoring the d-band centers (ε) of various metals is expected to balance the adsorption/desorption of multiple intermediates for water electrolysis, but remains challenging. Herein, porous ultrathin nanosheets consisting of V-doped Mo/Ni-based multi-heterostructures (V-MoN/NiN) are designed as bifunctional electrocatalysts for hydrogen and oxygen evolution reaction (HER/OER). V-substituted Mo-based polyoxometalates (POMs) were assembled with Ni(OH) to target multi-interface coupled Mo/Ni-based heterojunctions and precise V-doping. Theoretical calculations validate that V doping and heterostructure cause electron accumulation on the V-MoN side, which induces an upward shift in ε (Mo), strengthening HO adsorption. New active sites (V) and the nearby N sites are responsible for *OH and H* adsorption, thereby improving HER performance. After forming heterostructure, ɛ (Ni) shifts upward and significantly enhances the adsorption of various key intermediates (OH*, O* and OOH*). While, V-doping renders ɛ (Ni) slightly shift downward, which largely weakens the O* adsorption. The elaborate customizing of ε (Ni) effectively promotes the transition of O* to OOH*, thereby improving OER activity. Impressively, V-MoN/NiN manifests excellent activity, with overpotentials of 193 mV (HER) and 460 mV (OER) at 400 mA cm, significantly outperforming commercial Pt/C (306 mV) and RuO (512 mV). The assembled electrolyzer requires only 1.504 V@10 mA cm for overall water splitting with good durability. This study underscores the superiority of finely tailoring ε in triggering multi-site synergism.