Proton transport in electrochemically reduced graphene oxide: Enhancing H+/H2O selectivity

Abstract

Proton-selective membranes are prepared by electrochemical reduction of graphene oxide films in aqueous electrolytes. Rapid kinetics of oxygenated groups reduction was revealed by complementary FTIR- and XPS-spectroscopy giving rise to a partially reduced graphene oxide with C/O ratio in the range of 2–4. The reduction is accompanied by interstitial water loss and shrinkage of d-spacing from 1.15 nm, typical for graphene oxide, to graphene-like ∼0.36 nm as revealed by X-ray diffraction analysis. The presence of remaining oxygen groups in reduced graphene oxide enables fast transport of protons with Grotthuss hopping mechanism and diffusion coefficients in the range of 3–7∙10−11 m2 s−1 at 25 °C. At the same time, the reduction of GO layers hinders dramatically the transport of H2O molecules due to suppression of capillary condensation of water in the oxygen-deficient channels of the reduced graphene oxide providing the H+/H2O selectivity of up to 1400 upon electrochemical reduction. The suggested approach opens the avenue for the performance enhancement of carbon-based membranes for proton-selective transport in fuel cells and electrolyzers.