Surface modulation of NiCo2O4 nanowire arrays with significantly enhanced reactivity for ultrahigh-energy supercapacitors

Ternary NiCo2O4 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 NiCo2O4 nanowire arrays is developed, and the pseudopotential performance of the resulting NiCo2O4 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 NiCo2O4 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 NiCo2O4 cathode and a graphene anode, reaching an outstanding energy density of 92.2 Wh kg(-1) with outstanding long-term durability.