Enhanced Supercapacitor Performance with Hierarchically Porous Sno2 Embedded in Reduced Graphene Oxide Nanosheets

Abstract

The development of efficient supercapacitors for large-scale applications requires electrode materials with exceptional porous structure, and abundant ion-diffusion sites. In this study, we demonstrate that hierarchically porous SnO2 microspheres embedded within a reduced graphene oxide (rGO) matrix (SnO2/rGO-T) significantly enhance supercapacitor performance. By leveraging the Ostwald ripening process and the formation of high-energy crystal facets of SnO2 under hydrothermal and annealing conditions, SnO2/rGO-T microspheres are synthesized using a hydrothermal method in the presence of fluoride ions, followed by annealing at different temperatures (T = 300°C and 500°C). Notably, rGO acts as an in-situ crystal nucleus to support SnO2 growth, while fluoride ions direct the oriented attachment and growth of SnO2 particles. This endows the formation of uniform wrinkled ultrathin rGO nanosheets decorated with hierarchically SnO2 microspheres. These properties improve the energy and power density of the SnO2-rGO-T electrode towards supercapacitors than bare SnO2, however, this activity depended on the annealing temperature. Mainly, SnO2-rGO-500 outperforms SnO2-rGO-300, SnO2-rGO, and SnO2 with a specific capacitance of 241 F/g in 2M KOH electrolyte, energy density of 22.7 Wh/kg and power density of 900 W/kg at 1 A/g, and with capacitance retention of 89.7% after 10k cycles. This is due to enhanced crystallinity, porosity and the hierarchical structure of SnO2 within rGO allowing a better charge transfer after annealing at 500 oC. This study opens new gates for the rational design of efficient SnO2-rGO electrode using a simple and scalable synthesis methods for efficient energy storage devices.

Keywords: Supercapacitors, tin oxide, Reduced Graphene Oxide, crystalline and porous electrode, fluorine-ion etching