Pseudocapacitive Co9S8/graphene electrode for high-rate hybrid supercapacitors

Cobalt pentlandite (Co9S8) has recently emerged as a promising electrode material for energy storage devices. Herein, Co9S8/graphene hybrid is rationally synthesized through a facile hydrothermal method. Minor-sized Co9S8 flakes is finely-deposited on the surface of graphene sheet and an interconnected Co9S8/graphene architecture structure is obtained. The electrochemical test results show that Co9S8/graphene electrode delivers a remarkable charge capacity of 540 C g−1 within 1 min and 74.5% capacitance is retained within a discharge time of 14 s. A hybrid supercapacitor assembled with Co9S8-involved electrode delivers a high energy density of 37 Wh kg−1 at a power density of 170 W kg−1, and 15.3 Wh kg−1 can be maintained even at a high power density of 12 kW kg−1. The excellent electrochemical performance should be attributed to abundant active sites, enhanced charge-transfer characters and maximized capacitive contribution of Co9S8/graphene electrode.