Ordered Ionic-Liquid Channels Enable Fast Anhydrous Proton Conduction at up to 240°C for Fuel Cells

Intermediate-temperature electrochemical technologies offer a range of important advantages but require high-performance and robust anhydrous proton exchange membranes. Herein, we demonstrate that confinement of phosphonium-, imidazolium-, and sulphonium-based ionic liquids (ILs), within channels formed by stacked monolayers of boron nitride and graphene nanosheets functionalised with polyethyleneimine, provides robust and effective proton conductivity while suppressing bulk diffusion of the IL ions. We propose that the positively charged nanosheets might induce spatial ionic ordering, anchoring anions near the channel walls while concentrating protons and cations along the central region to establish parallel, continuous pathways for rapid proton transfer under anhydrous conditions. The resulting solid-state composite membranes exhibit stable anhydrous proton conductivities of up to 10^-2 S cm^{- 1} at 240 ± 1°C, outperforming many existing IL-based and polymer-based systems. When integrated into hydrogen-oxygen fuel cells, the [EMIM][NTf₂]-based membrane enables a peak power density of 82 ± 5 mW cm^-2 under anhydrous conditions at 240 ± 1°C and atmospheric pressure. In a broader context, this work presents a strategy for the design of membranes with properties tailored to a specific application, which can be achieved by tuning chemical structures of the confined IL and/or functional layers within the 2D channels.