Densely packed hybrid films comprising SnO2 and reduced graphite oxide for high-density electrochemical capacitors

Abstract

A densely packed film of reduced graphite oxide (rGO) typically experiences restacking problems after thermal or chemical reduction processes. This can limit adsorption or diffusion of electrolyte ions inside the film to store electrical charges, thus impeding its energy storage ability. To solve this problem, we propose using sub-5 nm-diameter SnO₂ nanoparticles (NPs) as spacers to prevent the restacking of the rGO film by the formation of a SnO₂/rGO heterostructure via a simple solution based two-step strategy. Compact rGO-based hybrid films, such as SnO₂/rGO, were created in the absence of any surfactants or polymers by using either a simple chemical redox reaction between graphene oxide (GO) and the SnCl₂ precursor or by adjusting the amount of SnO₂ NPs in the hybrids. Material and electrochemical characterizations reveal that only under certain experimental conditions, sensitive to the molar ratio of the SnCl₂ precursor to GO, would the fabricated hybrid films have uniformly dispersed SnO₂ NPs within the film and maintain a densely packed morphology with a high packing density of ca. 1.9 g cm⁻³. Furthermore, because the uniform SnO₂ NPs in the film act as effective spacers, the optimized hybrid film-based supercapacitor exhibits a remarkable enhancement of electrochemical performances, including high volumetric capacitances in both acidic and neutral electrolytes, superior rate performance, and long-term stability.