Construction of vacancies-enriched CuS/Fe2O3 with nano-heterojunctions as negative electrode for flexible solid-state supercapacitor

The application of supercapacitor is often restricted by unsatisfactory performance of negative electrodes and limited voltage window. Herein, the CuS/Fe2O3 nano-heterojunction with O and S vacancies is constructed by calcination and selective sulfurization, and applied as negative electrode for asymmetric supercapacitor devices. Compared with bare Fe2O3 and CuS, the heterojunction and defect endow the hybrid with improved conductivity, exposed full electrochemical active sites and enhanced charge transfer. Density functional theory (DFT) calculations suggest that the electronic interface reconstruction between CuS and Fe2O3 optimizes the electronic structure and accelerates the electron transport. Therefore, the heterostructured CuS/Fe2O3 exhibits superior supercapacitor negative performance with high capacitance (921 F g-1 at 1 A g-1) and good rate capability. After assembling an asymmetric solid-state supercapacitor (CuS/Fe2O3//MnO2 ASC) in a PVA/KOH gel, the device shows a high energy density of 56.6 Wh kg-1 at the power density of 900 W kg-1. In addition, employing polyvinyl alcohol/sodium alginate (PVA/SA/KOH) gel as the electrolyte, a flexible solid-state supercapacitor (CuS/Fe2O3//MnO2 SSC) provides 27.8 Wh kg-1 at 900 W kg-1. This work designs and fabricates defect-rich heterojunction between metal sulfide and oxide and provides insights into developing high-performance electrode materials for supercapacitors.