Controllable atoms implantation for inducing high valency nickel towards optimizing electronic structure for enhanced overall water splitting.

Adjusting the electronic structure and intrinsic activity of the active site of the catalyst based on atomic implantation is the crucial to realizing efficient electrochemical water splitting in alkaline media. Thus, we introduce vanadium (V) atoms with abundant vacant d orbitals as dopants into nickel selenides (NiSe), which has abundant variable valence states, and successfully synthesise three-dimensional bi-functional catalysts self-supported on Ni foam (NF). The electron structure characterisation reveals that, compared with the pure NiSe phase, the oxidation states of Ni cations and electron concentration at the Se site in V-NiSe increase due to the V doping. These changes are accompanied by changes in the electronic structure and active sites in V-NiSe. The as-generated V-NiSe nanorods exhibit an optimised electronic structure, high number of active sites and highly rough nanorod array structure with large electrochemically active surface area and in situ growth characteristics of conductive NF. Thus, the as-generated V-NiSe nanorods catalysts exhibit excellent bi-functional catalytic activity, with 50 mA⋅cm-2 at an overpotential of 270.2 and 251.2 mV for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER), respectively, in KOH (1 M). Water electrolysis using V-NiSe as both the anode and cathode requires a cell voltage of 1.76 V to drive 50 mA⋅cm-2, continuously operating for 80 h. This study provides a systematic understanding of the design of transition-metal catalysts using heteroatomic doping to control their electronic structure and catalytic activity.