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

[Display omitted] •Reduced graphene oxide based rGO/WO3·0.5H2O@Cu2S electrode is fabricated.•A maximum capacitance of 545.6 mF cm−2 is achieved for rGO/WO3·0.5H2O@Cu2S electrode.•The obtained supercapacitor delivered an outstanding energy density of 37.3 Wh kg−1.•The supercapacitor maintained 88% capacity retention after 10,000 cycles.•The supercapacitor showed excellence performances by glowing LEDs and digital stopwatch. 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 10,000 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.