Analysis of Reduced Graphene Oxides by X-ray Photoelectron Spectroscopy and Electrochemical Capacitance

Abstract

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...

Vanadium‐Ion Redox Reactions in a Three‐Dimensional Network of Reduced Graphite Oxide

“…Figure shows the XPS spectra of C 1s, O 1s, and N 1s in BGOs‐fd and BGOs‐fd‐1000. A typical C 1s and O 1s XPS spectra for GO were obtained for BGOs‐fd, which consisted of peaks assigned to an aromatic and aliphatic carbon at 284.6 eV, and carbon and oxygen atoms in an ether oxygen or hydroxylic group at 286.4 and 532.3 eV, respectively . The presence of residual nitrogen in an amine form was shown by the N 1s XPS spectrum of BGOs‐fd .…”

Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

“…However, deconvolution of this peak is essential for understanding the C1s XPS spectra of GO 35 . This is because the full width at half maximum (FWHM) is too large to assign the band to a single component (1 .3 eV) for GO, considering much smaller FWHM of the C=C peak from highly ordered pyrolytic graphite (0.8 eV) measured with the same experimental conditions 36 .…”

“…Therefore, recently, we have developed deconvolution of C1s XPS spectra in order to identify chemical states of GO, using reference samples with specific oxygen function group (OFG), C-H, C-C, or C=C bonding states 36,37 . In particular, our approach allows for the deconvolution of the peak at ca.…”

Synergetic effect of metal nickel and graphene as a cocatalyst for enhanced photocatalytic hydrogen evolution via dye sensitization

“…For the C 1 s spectra of the three GN composites, the peak intensities of the carbons with oxygen-containing groups (HO-C = O, C = O and C-OH) are very low, while those of C = C are considerably high, indicating the effective reduction of the three composites31. There is a very small fitting peak located at 284.0 eV which is assigned to the carbon of carbide nickel32, demonstrating the formation of C-Ni bond.…”