Graphene Oxide Membranes with Cerium-Enhanced Proton Conductivity for Water Vapor Electrolysis
Nur Laila Hamidah, Masataka Shintani, Aynul Sakinah Ahmad Fauzi, Ghina Kifayah Putri, Shota Kitamura, Kazuto Hatakeyama, Mitsuru Sasaki, Armando T. Quitain, Tetsuya Kida
Abstract
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.