Controlled growth of NiMoO4·H2O nanoflake and nanowire arrays on Ni foam for superior performance of asymmetric supercapacitors

Abstract

A facile hydrothermal method is developed for fabrication of large-scale NiMoO₄·H₂O arrays with robust adhesion on Ni foam. Importantly, the morphology of NiMoO₄·H₂O can be easily controlled to be nanoflake (H-NF) or nanowire (H-NW) arrays by using NH₄F as additive. The obtained nanoflake morphology delivers better electrochemical activity than that of nanowire. The electrochemical performance of anhydrous NiMoO₄ arrays obtained by annealing the NiMoO₄·H₂O has also been investigated for comparison. It is believed that the presence of the structural water of NiMoO₄ enhances the capacitive performance by making it a good ionic conductor. Furthermore, an asymmetric supercapacitor (ASC) is constructed using the as-prepared NiMoO₄·H₂O nanoflake arrays as the positive electrode and activated carbon (AC) as the negative electrode. The optimized ASC with an extended operating voltage range of 0–1.6 V displays excellent electrochemical performance with a high energy density of 53.8 W h kg⁻¹ at a power density of 239 W kg⁻¹ in addition to superior rate capability. Moreover, the H-NF//AC ASC device exhibits remarkable cycling stability with 73.4% specific capacitance retention after 4000 cycles. Our result shows that this unique NiMoO₄·H₂O nanoflake array is promising for electrochemical energy applications.