High-energy-density supercapacitors using supersonically sprayed water-based precursors comprising cobalt iron oxide and reduced graphene oxide nanosheets

A water-based iron oxide/cobalt/reduced graphene oxide (Fe₂O₃/Co/rGO) precursor was spray-coated via supersonic spraying onto a flexible substrate to fabricate supercapacitor electrodes. The inclusion of Co in Fe₂O₃ increased the number of electrochemical reaction sites and enhanced the local electron mobility, which in turn improved the overall energy storage capability of the electrodes. The Co salt concentration was varied to determine the optimal electrochemical performance. Supersonic spraying was utilized to coat rGO sheets, on which the bimetallic CoFe₂O₃ particles were evenly distributed. The uniform coating of rGO and its excellent electrical conductivity increased the electron mobility of the electrode and provided shorter ionic diffusion pathways. Furthermore, the catastrophic impact of supersonic spraying led to the exfoliation of the rGO sheets, which increased the surface area and enhanced the adherence of the CoFe₂O₃ particles to the substrate. This rGO exfoliation also enabled the accommodation of the CoFe₂O₃ particles between the exfoliated graphene sheets, thereby enhancing electron transport throughout the electrode. The optimal sample exhibited a specific capacitance of 1.11 F·cm⁻² at a current rate of 2 mA·cm⁻², energy density of 0.62 mWh·cm⁻² at a power density of 8 mW·cm⁻², and capacitance retention of 89% after 10,000 charge-discharge cycles.