Morphology engineering of nickel molybdate hydrate nanoarray for electrocatalytic overall water splitting: from nanorod to nanosheet.

The morphology of nano-arrays plays an important role in their applications for catalysis, energy, environment. However, the morphology modulation of nano-arrays generally involves complex optimization of synthetic conditions including surfactants, pH, and solvent. In this work, we synthesize a NiMoO·HO nano-array by a simple hydrothermal method under mild conditions (pH = 6.47, aqueous solution, and without the aid of surfactants). The morphology modulation of the NiMoO·HO nano-array is realized by simply changing the hydrothermal temperature. When the hydrothermal temperature below 150 °C, a NiMoO·HO nanorod array is obtained. While the hydrothermal temperature is as high as 180 °C, the array on Ni foam is nanosheet instead of nanorod. The NiMoO·HO nanorod array synthesized at 150 °C shows a superior water splitting activity compared to the NiMoO·HO nanosheet array, affording a large current density of 10 mA cm at an overpotential of <240 and 200 mV toward oxygen evolution reaction and hydrogen evolution reaction, respectively. Furthermore, the electrolyzer using NiMoO·HO nanorod array as both anode and cathode electrodes for catalyzing overall water splitting exhibits great performance, obtaining a current density of 10 mA cm at 1.67 V, comparable to the integration of commercial noble-metal Pt/C and IrO electrodes.