Large increment in the charge storage performance of CoSb2O6-reduced graphene oxide (rGO) composite -probing the role of rGO through experiment and theoretical analyses

Abstract

We present a detailed electrochemical comparison between cobalt antimony oxide and its reduced graphene oxide composite, prepared through a combination of hydrothermal and ultrasonic synthesis. The structural, morphological, and compositional properties of the as-synthesized material are detailed through comprehensive characterization techniques. In a three-electrode configuration, the composite CoSb₂O₆/rGO exhibited a specific capacitance value of 1000 F/g at a mass-normalized current of 2 A/g, which is at least 5-fold higher than that of pristine CoSb₂O₆ (i.e., 195.5 F/g at a mass-normalised current of 2 A/g). It shows high-capacity retention of 93.18 %, over 3000 cycles. We have also tested a two-electrode symmetric device, fabricated from CoSb₂O₆/rGO composite, that shows a specific capacitance of 227.79 F/g, at a mass-normalised current of 1 A/g. The CoSb₂O₆/rGO composite yields energy and power densities of 38.28 Wh/kg and 10.08 kW/kg, respectively, and exhibits a cyclic stability of 98.54% even after 10,000 cycles. Further, we have employed density functional theory simulations to elucidate the structure and electronic characteristics of pristine CoSb₂O₆ and CoSb₂O₆/rGO composite systems. The enhancement in the electronic states near the Fermi level, resulting from the charge transfer from rGO to CoSb₂O₆, indicates improved conductivity in the CoSb₂O₆/rGO composite system. The considerably lower diffusion energy barrier and enhanced quantum capacitance of CoSb₂O₆/rGO compared to CoSb₂O₆ contribute to the superior supercapacitance performance, which supports our experimental findings.