Uniform phosphorus doped CoWO4@NiWO4 nanocomposites for asymmetric supercapacitors

Transition metal oxides are widely used as the electrodes of supercapacitor attributing to their low cost and cycling stability. Herein, phosphorus doped NiWO4@CoWO4 nanocomposites are directly grown on nickel foams as supercapacitor electrodes. With the incorporating of P atom, many nanoparticles and O vacancies are formed on the surface of the optimized P-NiWO4@CoWO4. Accordingly, the P-NiWO4@CoWO4 exhibits a good cycling stability and high specific capacitance of 5.11 F cm-2 at 1 mA cm-2 (or a specific capacitance 1683.4 F g-1 at 1 A g-1), nearly 2.5 times higher than that of NiWO4@CoWO4. P-NiWO4@CoWO4 electrode also shows great rate capability with 88% capacitance retention when the current density is increased ten-fold. Moreover, an asymmetric supercapacitor (ASC) assembled with P-NiWO4@CoWO4 as the positive electrode and active carbon as the negative electrode with 6 M KOH as the electrolyte displays an excellent energy density of 0.15 mWh cm-2 at a power density of 0.79 mW cm-2 (26.8 Wh kg-1 at 824.6 W kg-1).