A Few Atoms Thick Nickel–Cobalt Oxides Mesoporous Nanosheets and Their Arrays on Ni Foam for Supercapacitors with Ultra-Long Cycling Lifespan

Abstract

Abundant electroactive sites, good electrical conductivity and rich channels are essential for high-performance pseudocapacitive materials, but their realization at the same time is still a great challenge. In this study, we prepare a few atoms thick and mesoporous nickel–cobalt (Ni−Co) oxides nanosheets for supercapacitors. The Ni−Co oxides have been synthesized via combining hydrothermal method with subsequent annealing treatment, which is very robust for the Ni−Co oxides with tuneable compositions and structures. The ultrathin and mesoporous nanosheets give rise to ultrahigh atom ratio at surface for high electroactive sites and abundant channels. In addition, by controlling the Ni to Co ratio and further supported on Ni foam, the electrochemical activity can be further promoted. As a result, the Ni0.5Co0.5O shows much higher specific capacitance values of 761 and 1616 F g−1 at 1 A g−1 for powder sample and its arrays on foam, which are both gradually increasing with repeated cycling. When used to assemble asymmetric supercapacitor, the two-electrode system shows a high energy density of 34.6 Wh kg−1 at 750 W kg−1, attractive power performance of 22.5 kW kg−1 at 21.5 Wh kg−1 with ultralong cycling stability (87% of capacitance retention after 10000 cycles).