High rate capability of mesoporous NiWO4-CoWO4 nanocomposite as a positive material for hybrid supercapacitor

Nickel-based materials are promising positive electrode for hybrid supercapacitor due to their high theoretical specific capacity. The main obstacle preventing their practical applications is the low conductivity which limits rate capability of supercapacitors. Considering the good rate capability of CoWO4 and the high specific capacity of NiWO4, we synthesize a series of mesoporous NiWO4-CoWO4 nanocomposite with different Co/Ni molar ratios by a chemical co-precipitation method, and the materials were fully characterized by XRD, XPS, FESEM, TEM and N2 adsorption-desorption measurements. Impressively, the nanocomposite shows a large surface area of 150.7 m2 g−1, which resulting in the enhanced electrochemical performance. In specific, the NiWO4-CoWO4 electrode with a Co/Ni molar ratio of 2:8 has the highest specific capacity of 196.7 C g−1 at 0.5 A g−1. Compared to individual NiWO4 and CoWO4, it also exhibits improved rate capability which decreases less than one third of the initial value as the current is increased 20 times. Finally, we fabricate a NiWO4-CoWO4//AC hybrid supercapacitor whose storage energy density is as high as 30.1 Wh kg−1 even at a large power density of 200 W kg−1. This work provides a novel way to fabricate electrode materials with high electrochemical performance for supercapacitors and other energy storage devices.