Supercapacitor Electrodes from the in Situ Reaction between Two-Dimensional Sheets of Black Phosphorus and Graphene Oxide

Two-dimensional materials show considerable promise as high surface area electrodes for energy-storage applications such as supercapacitors. A single sheet of graphene possesses a large specific surface area because of its atomically thin thickness. However, to package this area efficiently in a device, it must be confined within a finite three-dimensional volume without restacking of the sheet faces. Herein, we present a method of maintaining the high surface area through the use of a hybrid thin film in which few-layer exfoliated black phosphorus (BP) reduces graphene oxide (GO) flakes. When the film is exposed to moisture, a redox reaction between the BP and the GO forms an interpenetrating network of reduced GO (RGO) and a liquid electrolyte of intermediate phosphorus acids HxPOy. The presence of the liquid HxPOy electrolyte in the RGO/HxPOy film stabilizes and preserves an open-channel structure enabling rapid ion diffusion, leading to an excellent charging rate capability (up to 500 mV s(-1) and retaining 62.3% of initial capacitance at a large current density of 50 A g(-1)) when used as electrodes in supercapacitors.