Surface-functionalized boron nanosheets and their assembled suprastructures with unprecedented proton-transport properties.

Two-dimensional (2D) boron nanomaterials have received considerable attention due to their distinct physicochemical properties in contrast to bulk boron. However, the susceptibility to oxidation in air has limited their practical applications. In this study, we synthesize an environmentally stable bifunctionalized boron nanosheet via a wet chemical route. By lyophilization, we have hierarchically assembled the boron nanosheets into various well-ordered macroscopic forms, which exhibit unique structural features, such as stacking-induced nanochannels for proton transport. The resulting suprastructures show exceptionally high proton conductivity (∼90 mS cm -1 at 85 °C) and humidity sensitivity (response >40 000% at 97% RH). These findings demonstrate the immense potential of boron nanomaterials in electrochemical applications.