Large improvement in the charge storage performance of a CoSb2O6–reduced graphene oxide (rGO) composite – probing the role of rGO through experiments and theoretical analyses

Abstract

We present a detailed electrochemical comparison between cobalt antimony oxide (CoSb₂O₆) and its reduced graphene oxide (rGO) composite, prepared through a combination of hydrothermal and ultrasonic synthesis. The structural, morphological, and compositional properties of the as-synthesized material have been investigated through comprehensive characterization techniques. In a three-electrode configuration, the CoSb₂O₆/rGO composite exhibited a specific capacitance value of 1000 F g⁻¹ at a mass-normalized current of 2 A g⁻¹, which is at least 5-fold higher than that of pristine CoSb₂O₆ (i.e., 195.5 F g⁻¹ at a mass-normalised current of 2 A g⁻¹). It shows a high capacity retention of 93.18% over 3000 cycles. We have also tested a two-electrode symmetric device, fabricated from the CoSb₂O₆/rGO composite, which shows a specific capacitance of 227.79 F g⁻¹ at a mass-normalised current of 1 A g⁻¹. The CoSb₂O₆/rGO composite yields energy and power densities of 38.28 Wh kg⁻¹ and 10.08 kW kg⁻¹, respectively, and exhibits a cyclic stability of 98.54% even after 10 000 cycles. Furthermore, 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 of 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.