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

Abstract

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 NiMoO₄·H₂O 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 NiMoO₄·H₂O nano-array is realized by simply changing the hydrothermal temperature. When the hydrothermal temperature below 150 °C, a NiMoO₄·H₂O 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 NiMoO₄·H₂O nanorod array synthesized at 150 °C shows a superior water splitting activity compared to the NiMoO₄·H₂O nanosheet array, affording a large current density of 10 mA cm⁻² at an overpotential of <240 and 200 mV toward oxygen evolution reaction and hydrogen evolution reaction, respectively. Furthermore, the electrolyzer using NiMoO₄·H₂O nanorod array as both anode and cathode electrodes for catalyzing overall water splitting exhibits great performance, obtaining a current density of 10 mA cm⁻² at 1.67 V, comparable to the integration of commercial noble-metal Pt/C and IrO₂ electrodes.