In-situ prepared NiMoO4 nanocrystals synergizes with nickel micro-tubes with hydrodynamic effects for energy-saving watersplitting.

[Display omitted] • A urea assisted hydrogen evolution device with high energy saving efficiency was proposed. • NiMoO 4 NC/NT electrocatalyst exhibited excellent activity for both UOR and HER. • The flow field effect assisted electrocatalysis can achieve the best catalytic activity. • The structures of NiMoO 4 nanocrystalline were synthesized in situ for the first time. • The results of DFT calculation prove that Mo is the priority adsorption site for urea molecule. Coupling hydrogen evolution reaction (HER) with urea oxidation reaction (UOR) can significantly reduce the cell voltage, but also alleviate the environmental pollution caused by urea. We prepared NiMoO 4 nanocrystals (NC) in situ and cooperated with the hydrodynamics effect of nickel-micro tubes (NT), so that nanocrystals growing inside and outside the tube wall can fully react with electrolyte under the effect of flow field during the process of liquid flow, and achieve the best catalytic activity. Significantly, NiMoO 4 NC 400 /NT as electrode in coupled system achieving an ultralow cell voltage. And DFT calculations suggested a lattice oxygen involved urea oxidation reaction pathway with Ni-Mo site as the active site. Our approach can give a straightforward synthesis method for in-situ nanocrystal preparation, as well as break the shackles of standard water electrolysis and provide a new way to produce energy-saving hydrogen. [ABSTRACT FROM AUTHOR]