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 H<sub><i>x</i></sub>PO<sub><i>y</i></sub>. The presence of the liquid
H<sub><i>x</i></sub>PO<sub><i>y</i></sub> electrolyte
in the RGO/H<sub><i>x</i></sub>PO<sub><i>y</i></sub> film stabilizes and preserves an open-channel structure enabling
rapid ion diffusion, leading to an excellent charging rate capability
(up to 500 mV s<sup>–1</sup> and retaining 62.3% of initial
capacitance at a large current density of 50 A g<sup>–1</sup>) when used as electrodes in supercapacitors
