Ultrathin Ni-Mo oxide nanoflakes for high-performance supercapacitor electrodes

Highlights: • Ultra-thin porous Ni-Mo oxide nanoflakes self-assemble on stainless steel via a SILAR method. • Large electrochemically-active surface area, enhanced ion diffusion and robust adhesion result in superior performance. • High specific capacitance of 1180 F/g and energy density of 119 Wh/kg at 1 A/g are achieved. Supercapacitors based on nanomaterial electrodes exhibit great potential as power sources for advanced electronic devices. From a practical viewpoint, it is desirable to fabricate highly active and sustainable nanomaterial electrodes consisting of non-precious elements using a simple technique in a controllable way. In this work, we report the synthesis of a self-assembled ultra-thin porous nanoflake Ni-Mo oxide (NMO) film using the successive ionic layer adsorption and reaction (SILAR) technique. The nanoflake NMO thin film electrode with a large electrochemically active surface area of ∼108 cm⁻² exhibits a high specific capacitance of 1180 Fg⁻¹ at a current density of 1 Ag⁻¹ and excellent rate capability, with a negligible capacity loss of 0.075% per cycle. Even at a high current rate of 10 A g⁻¹ it retains a capacity of 600 Fg⁻¹. The highest energy and power densities obtained are 119 Whkg⁻¹ and 15.7 kWkg⁻¹, respectively. Electrochemical impedance spectroscopy analyses reveal that the electrode has considerably low charge transfer resistance. The observed excellent electrochemical energy storage performance of the nanoflake NMO electrode with a nanoporous surface is due to the synergetic effects of the large electrochemically active surface area, enhanced ion diffusion, and improved electrical conductivity.