Graphene Oxide Membranes with Cerium-Enhanced Proton Conductivity for Water Vapor Electrolysis

Proton conduction in graphene oxide (GO) allows for a variety of electrochemical applications. This study focuses on the application of a stacked GO nanosheet membrane for water vapor electrolysis. It was found that the use of expanded graphite in the Tour method effectively produced GO nanosheets having a higher oxidation state (62 at. %) with a shortened synthesis time. The interlayer spacing of a membrane was considerably increased by coupling the highly oxidized nanosheets with Ce ions. The Ce-modified self-standing GO membrane (260 μm) showed an improved stability in water and a high proton conductivity comparable to that of Nafion at room temperature. The remarkable improvement in proton diffusion was attained by the Ce-assisted expansion of the interlayer spacing. The unique features of the Ce ions that interact with GO nanosheets were also discussed. Concentration cell measurements indicated that the Ce-modified membrane is a pure proton conductor at room temperature. The Ce-modified membrane sandwiched with the IrO2–Al2O3 anode and Pt/C cathode efficiently converted water vapor to hydrogen and oxygen in a 2:1 ratio at room temperature and 40 °C. Our results demonstrate the promising capability of carbon-based membranes for electrochemical energy devices.