Regulating the Frontier Orbital Interactions of Ru and NiO Support via Rare Earth Atoms to Optimize Interfacial Water for Enhanced Hydrogen Evolution

Metal/support-type materials with tunable frontier orbital energy gap are promising electrocatalysts for water splitting, while accurately tailoring their frontier orbital interaction to optimize the pair of metal−adsorbate and metal−support interactions and further to simultaneously boost activity and stability still remains challenging. Herein, density functional theory (DFT) calculations were first employed to predict the influence of six light rare-earth (La, Ce, Pr, Nd, Sm, and Eu) single atoms on support frontier orbitals, and the results reveal that La exhibits the strongest capability to modulate the lowest unoccupied molecular orbital (LUMO) energy level of the NiO support. Experimental and DFT evidence further demonstrate that the elevated LUMO of the support can reduce the energy gap with the highest occupied molecular orbital (HOMO) of Ru atoms, which optimizes the interfacial water adsorption and promotes the Ru-NiO orbital hybridizations, thus leading to enhanced activity and stability toward hydrogen evolution. As expected, the as-prepared Ru/La 0.05 NiO electrode exhibited a low overpotential of 37 mV at 10 mA cm −2, a lower Tafel slope of 64.79 mV dec −1, and long-term stability of 420 h at 100 mA cm −2 . Our findings provide a general descriptor for the rational regulation of metal−support interactions to consequently boost favorable interfacial water adsorption for hydrogen production.