Ultrahigh moisture electric output of oxidation-controlled and ion-intercalated graphene oxide films in the low humidity range

Abstract

Moisture electric generators (MEGs), which can harvest a large amount of ubiquitous water energy, are attracting considerable attention. This study simultaneously increases the moisture-induced voltage and current in graphene oxide (GO) films by controlling the oxidation degree and the sulfate ion intercalation, respectively. Controlling the oxidation degree of sulfate-ion-intercalated GO (sGO) films allows us to regulate the crystallinity. The sGO films with higher crystallinity exhibit higher moisture-induced voltages. Increasing the content ratio of sulfate ions increases the moisture-induced current density because of the widened proton conduction channels and the enhanced water uptake ability. The enhanced water uptake ability allows us to obtain a high electric output even at low humidity. The single-unit MEGs of sGO films exhibit an ultrahigh output power density of 47 μW cm⁻² at relative humidity (RH) of 30%, which is approximately 2500 times higher than that reported for a single-unit GO material (RH = ∼30%). Although the impact of ion intercalation on MEG performance has been unknown in the MEG field, this study uncovers that sulfate ion intercalation leads to high moisture-induced current density and high water uptake ability at low humidity. The outstanding approach of controlling the oxidation degree and intercalating sulfate ions opens a pathway for high-performance versatile MEGs.