Fabrication of three-dimensionally heterostructured rGO/WO3.0.5H2O@Cu2S electrodes for high-energy solid-state pouch-type asymmetric supercapacitor

Abstract Advanced nanostructured electrodes containing more electroactive sites are essential to develop the high rate performance supercapacitors (SCs). Herein, we engineered two-dimensional (2D) reduced graphene oxide (rGO) on the diamond-like cubic tungsten oxide (WO3.0.5H2O), which was further decorated with the plant-like monoclinic copper sulfide (Cu2S) to form a three-dimensionally (3D) heterostructured rGO/WO3.0.5H2O@Cu2S electrode using a simple two-step hydrothermal method. This electrode exhibited a 1.5-fold higher areal capacitance of 545.6 mF cm-2 (974.4 F g-1) over the WO3.0.5H2O based electrode in the redox active Na2SO4:K4[Fe(CN)6] electrolyte. Meanwhile, the asymmetric pouch-type solid-state supercapacitor (APSC) was successfully operated at a high potential of 2 V with an excellent areal capacitance of 235.4 mF cm-2 (269 F g-1) at 5 mV s-1, an energy density of 32.6 μWh cm-2 (37.3 Wh kg-1), cycling stability of 88 % over 10000 rapid charging/discharging cycles and a short relaxation time of 0.084 s at a frequency of 11.9 Hz. In addition, the density functional theory (DFT) simulations were used to explore the origin of the superb performance. It is found that the nanosheet-state graphene at the interface of WO3.0.5H2O and Cu2S could create the fast-electronic pathway, shorten the diffusion distance and give structural reliability. This novel strategy is expected to offer an effective way to develop new-generation supercapacitors with ultra-high energy storage ability for the practical application.