Hydrogen production by membrane water electrolysis has attracted tremendous attention because of its benefits, which include easy separation of hydrogen and oxygen, no carbon emissions, and the possibility to store hydrogen fuel as an electricity source. Here, we study water vapor electrolysis using a proton-conducting membrane comprising graphene oxide (GO) nanosheets. The GO membrane shows good through-plane proton conductivity, as confirmed by concentrationcell measurements, complex impedance spectroscopy, and hydrogen pumping experiments. The results also confirm that most carriers in the GO membrane are protons. The GO membrane fitted with Pt/C and IrO2-Al2O3 as the cathode and the anode, respectively, efficiently electrolyzes humidified air to produce hydrogen and oxygen at room temperature, which indicates bright prospects for this carbon-based electrochemical device.

Solid electrolyte interface (SEI) is a critical factor that influences battery performance. SEI layer is formed by the decomposition of organic and inorganic compounds after the first cycle. This study investigates SEI formation as a product of electrolyte decomposition by the presence of flouro‐o‐phenylenedimaleimaide (F‐MI) additive. The presence of fluorine on the maleimide‐based additive can increase storage capacity and reversible discharge capacity due to high electronegativity and high electron‐withdrawing group. The electrolyte containing 0.1 wt% of F‐MI‐based additive can trigger the formation of SEI, which could suppress the decomposition of remaining electrolyte. The reduction potential was 2.35 to 2.21 V vs Li/Li+ as examined by cyclic voltammetry (CV). The mesocarbon microbeads (MCMB) cell with F‐MI additive showed the lowest SEI resistance (Rsei) at 5898 Ω as evaluated by the electrochemical impedance spectroscopy (EIS). The morphology and element analysis on the negative electrode after the first charge‐discharge cycle were examined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X‐ray photoelectron spectroscopy (XPS). XPS result showed that MCMB cell with F‐MI additive provides a higher intensity of organic compounds (RCH2OCO2Li) and thinner SEI than MCMB cell without an additive that provides a higher intensity of inorganic compound (Li2CO3 and Li2O), which leads to the performance decay. It is concluded that attaching the fluorine functional group on the maleimide‐based additive forms the ideal SEI formation for lithium‐ion battery.

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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 IrO 2 −Al 2 O 3 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.