Proton conductivities of layered solid electrolytes can be improved by minimizing strain along the conduction path. It is shown that the conductivities (σ) of multilayer graphene oxide (GO) films (assembled by the drop-cast method) are larger than those of single-layer GO (prepared by either the drop-cast or the Langmuir-Blodgett (LB) method). At 60% relative humidity (RH), the σ value increases from 1×10(-6) S cm(-1) in single-layer GO to 1×10(-4) and 4×10(-4) S cm(-1) for 60 and 200 nm thick multilayer films, respectively. A sudden decrease in conductivity was observed for with ethylenediamine (EDA) modified GO (enGO), which is due to the blocking of epoxy groups. This experiment confirmed that the epoxide groups are the major contributor to the efficient proton transport. Because of a gradual improvement of the conduction path and an increase in the water content, σ values increase with the thickness of the multilayer films. The reported methods might be applicable to the optimization of the proton conductivity in other layered solid electrolytes.

The surface charge of various anionic unilamellar nanosheets, such as graphene oxide (GO), Ti0.87O2(0.52-), and Ca2Nb3O10(-) nanosheets, has been successfully modified to be positive by interaction with polycations while maintaining a monodispersed state. A dilute anionic nanosheet suspension was slowly added dropwise into an aqueous solution of high molecular weight polycations, which attach on the surface of the anionic nanosheets via electrostatic interaction. Surface modification and transformation to positively charged nanosheets were confirmed by various characterizations including atomic force microscopy and zeta potential measurements. Because the sizes of the polycations used are much larger than the nanosheets, the polymer chains may run off the nanosheet edges and fold to the fronts of the nanosheets, which could be a reason for the continued dispersion of the modified nanosheets in the suspension. By slowly adding a suspension of polycation-modified nanosheets and pristine anionic nanosheet dropwise into water under suitable conditions, a superlatticelike heteroassembly can be readily produced. Characterizations including transmission electron microscopy and X-ray diffraction measurements provide evidence for the formation of the alternately stacked structures. This approach enables the combination of various pairs of anionic nanosheets with different functionalities, providing a new opportunity for the creation of unique bulk-scale functional materials and their applications.

Many unique properties of graphene oxide (GO) strongly depend on the oxygenated functional groups and morphologies. Here, the photoreaction process is demonstrated to be very useful to control these factors. We report the fast, simple production of nanopores in porous GO via photoreaction in O2 under UV irradiation at room temperature. Quantitative analysis using X-ray photoelectron spectroscopy showed that nanopores were produced in areas of oxygenated groups (sp3 carbon bonds), creating porous reduced graphene oxide (rGO). The photoreaction mechanism was proposed on the basis of changes in the number of oxygenated groups. Proton conduction occurred at the basal plane of epoxide groups in virgin GO, even at low humidity, and at carboxyl groups for porous rGO at high humidity. Thus, GO and rGO samples with various morphologies, oxygenated functional groups, and conduction types can be easily fabricated by controlling the photoreaction conditions.

Reduced graphene oxide (rGO) and reduced graphite oxide (rGtO) were analyzed by X-ray photoelectron spectroscopy. rGO and rGtO were prepared by photochemical, electrochemical, hydrazine-assisted, and thermal reduction of graphene oxide (GO) and graphite oxide (GtO). The number of CH defects increased for the photochemical and electrochemical reduction, whereas a direct increase in the number of C=C bonds was observed for thermal and hydrazine-assisted reduction. Cyclic voltammograms showed that the electrochemical capacitance of rGtO increased with the number of CH defects.Reduced graphene oxide (rGO) has several advantages over graphene oxide (GO) for use in electrical devices. Typically, rGO is prepared by the thermal, 14 hydrazine-assisted, 47 or photochemical 810 reduction of GO. These treatments produce similar increases in the electrical conductivity, and the increase depends on the treatment conditions. Compositional differences have also been observed; for example, N doping has been detected after hydrazine-assisted reduction. 47 However, a detailed analysis of the functional groups in rGOs prepared by various reduction methods, particularly of the non-oxygenated functional groups (sp 3 CC, sp 3 CH, and sp 2 C=C bonds), has never been performed.We analyzed GO and rGO by X-ray photoelectron spectroscopy (XPS) and deconvoluting the C1s binding energies of the functional groups. Analysis of the CH defects is very important because they are key functional groups in rGO supercapacitor electrodes. 11,12 In this study, we demonstrate the importance of the CH defects on the electrochemical capacitance and the dependence of the differences in the functional groups of the rGO samples, particularly the CH defects, on the reduction method.Two types of GO samples were prepared by different methods. The rGO sample was prepared by the conventional Hammers' method, 13 using 98% graphite powder (Wako Chemicals) as the starting material. The graphite oxide (GtO; multilayered GO) sample was prepared by the electrochemical oxidation of glassy carbon (GC; BAS) in 0.1 M Na 2 SO 4 (Wako Chemicals) at 2.0 V (vs. Ag/AgCl) for 30 min.11 The electrochemical reduction of GtO was performed at ¹1.1 V in 0.1 M Na 2 SO 4 for 30 min. Photochemical, thermal, and hydrazineassisted reduction were conducted on both samples. The photochemical reduction was carried out under a 500-W Hg lamp for 1 h in H 2 . The thermal reduction was carried out in Ar at 300°C for 30 min. For the hydrazine-assisted reduction, the samples were immersed in a 10 M aqueous hydrazine solution at 60°C for 6 h.The XPS measurements were carried out using a Thermo Scientific SigmaProbe and monochromatic Al K¡ radiation. The instrument work function was calibrated to give a binding energy (BE) of 83.95 eV for the Au4f 7/2 line for metallic gold. The spectrometer dispersion was adjusted to give a BE of 368.25 eV for metallic Ag3d 5/2 and 932.65 eV for metallic Cu2p 3/2 . The instrument base pressure was 1 © 10 ¹9 mbar. High-resolution spectra were collected with a pass...