Fabricating Co9S8@NiWO4 Electrode toward Record Area Capacitance of 18.8 F cm–2 for High Performance Supercapacitor

Realizing ultrahigh area capacitance based on suitable electrodes is a challenge for supercapacitors. In this work, an electrode is designed consisting of Co9S8 nanotubes and NiWO4 nanoparticles (named Co9S8@NiWO4) and fabricated by a hydrothermal process. The Co9S8@NiWO4 electrode realizes a record area capacitance of 18.8 F cm-2 at a current density of 5 mA cm-2 among the reports in the literature. The corresponding asymmetric supercapacitor shows high energy density of 0.48 mW h cm-2 at 2.42 mW cm-2 and superior cyclic stability of 79.2% retention over 7000 cycles at 10 mA cm-2. The great promotion in performance of Co9S8@NiWO4 electrode is synergistically attributed to high intrinsic theoretical capacitances of compounds, abundance polyvalent states, improved conductivity, and increases in reaction sites and rate of the electrode. This work provides a new route for designing highly efficient electrode for developing supercapacitors with high performance in practical applications.