Green synthesis of Ni3S2/rGO as binder-free electrodes for supercapacitor application

Nickel sulfide/reduced graphene oxide (Ni3S2/rGO) composite microparticles directly anchored on nickel foam were developed via a convenient electrodeposition technique and succeeding calcination procedure with graphene oxide (GO) as oxidants and L-cysteine as sulfur source. The role of GO component and its concentration on the morphologies, structures and electrochemical behaviors were distinctly determined. On account of the synergistic effects from rGO layers and nickel sulfides, the as-synthesized Ni3S2/rGO-90 composites were verified as efficient binder-free electrodes, which showed superior electrochemical properties with the largest specific capacitance (1587.2 F g-1 at 1 A g-1) and long cycling life (87.8% capacity reservation through 5000 charge/ discharge cycles) owing to their enhanced conductivity, enlarged specific surface area, abundant active sites. Furthermore, an asymmetric supercapacitor was designed and developed employing the optimal Ni3S2/rGO and activated carbon electrodes i.e. Ni3S2/rGO-90//AC, which presented an energy density of 63.7 W h kg- 1 at a power density of 752.3 W kg- 1 and still reserved 26.2 W h kg- 1 at 14947.7 W kg- 1 as well as a splendid durability (80.5% of original capacitance through 5000 consecutive cycles).