Active Site Engineering and Theoretical Aspects of "Superhydrophilic" Nanostructure Array Enabling Efficient Overall Water Electrolysis.

The rational design of noble metal-free electrocatalysts holds great promise for cost-effective green hydrogen generation through water electrolysis. In this context, here, the development of a superhydrophilic bifunctional electrocatalyst that facilitates both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline conditions is demonstrated. This is achieved through the in situ growth of hierarchical NiMoO 4 @CoMoO 4 ·xH 2 O nanostructure on nickel foam (NF) via a two-step hydrothermal synthesis method. NiMoO 4 @CoMoO 4 ·xH 2 O/NF facilitates OER and HER at the overpotentials of 180 and 220 mV, respectively, at the current density of 10 mA cm -2 . The NiMoO 4 @CoMoO 4 ·xH 2 O/NF ǁ NiMoO 4 @CoMoO 4 ·xH 2 O/NF cell can be operated at a potential of 1.60 V compared to 1.63 V displayed by the system based on the Pt/C@NFǁRuO 2 @NF standard electrode pair configuration at 10 mA cm -2 for overall water splitting. The density functional theory calculations for the OER process elucidate that the lowest ΔG of NiMoO 4 @CoMoO 4 compared to both Ni and NiMoO 4 is due to the presence of Co in the OER catalytic site and its synergistic interaction with NiMoO 4 . The preparative strategy and mechanistic understanding make the windows open for the large-scale production of the robust and less expensive electrode material for the overall water electrolysis.