Surface Modulation of NiCo 2 O 4 Nanowire Arrays with Significantly Enhanced Reactivity for Ultrahigh-Energy Supercapacitors

Abstract Ternary NiCo 2 O 4 is attracting substantial attention as electrode material for high-performance supercapacitors. Unfortunately, it still suffers from low specific capacitance in terms of its relative low conductivity. Herein, an effective and general surface modulation strategy involving in-situ phosphatization of NiCo 2 O 4 nanowire arrays is developed, and the pseudopotential performance of the resulting NiCo 2 O 4 nanowire arrays is dramatically increased. The surface modulation can increase active sites, enhance conductivity and accelerate charge transfer kinetics. Importantly, at a large current density of 20 A g −1 , the optimal NiCo 2 O 4 electrode possesses a significant specific capacitance of 1642 F g −1 . When the current density increases from 2 to 20 A g −1 , an excellence rate capability with 81.3% specific capacitance is maintained. Also, the resulting electrode owns excellent long-term cycle stability that the specific capacitance only decreases 4.3% after 10,000 cycles. Moreover, an advanced asymmetric supercapacitor device is build up based on the optimal NiCo 2 O 4 cathode and a graphene anode, reaching an outstanding energy density of 92.2 Wh kg −1 with outstanding long-term durability.