Functionalized graphene oxide-reinforced electrospun carbon nanofibers as ultrathin supercapacitor electrode

Graphene oxide has been used widely as a starting precursor for applications that cater to the needs of tunable graphene. However, the hydrophilic characteristic limits their application, especially in a hydrophobic condition. Herein, a novel non-covalent surface modification approach towards graphene oxide was conducted via a UV-induced photo-polymerization technique that involves two major routes; a UV-sensitive initiator embedded via pi-pi interactions on the graphene planar rings, and the polymerization of hydrophobic polymeric chains along the surface. The functionalized graphene oxide successfully achieved the desired hydrophobicity as it displayed the characteristic of being readily dissolved in organic solvent. Upon its addition into a polymeric solution and subjected to an electrospinning process,non-woven random nanofibers embedded with graphene oxide sheets were obtained. The prepared polymeric nanofibers were subjected to two-step thermal treatments that eventually converted the polymeric chains into a carbon-rich conductive structure. A unique morphology was observed upon the addition of the functionalized graphene oxide, whereby the sheets were embedded and intercalated within the carbon nanofibers and formed a continuous structure. This reinforcement effectively enhanced the electrochemical performance of the carbon nanofibers by recording a specific capacitance of up to 140.10 F/g at the current density of 1 A/g, which was approximately three folds more than that of pristine nanofibers.It also retained the capacitance up to 96.2% after 1000 vigorous charge/discharge cycles. This functionalization technique opens up a new pathway in tuning the solubility nature of graphene oxide towards the synthesis of a graphene oxide-reinforced polymeric structure.

Structural Thermal Stability of Graphene Oxide-Doped Copper–Cobalt Oxide Coatings as a Solar Selective Surface

3d transition metal oxides based thin film coatings such as copper–cobalt oxides exhibit high absorption in the visible region and low emittance in the infrared to far-infrared region of the solar spectrum which is favourable for use as potential selective surface materials in photothermal devices. These materials have the potential to minimize heating while increasing absorption in the operative spectrum range and therefore achieve higher solar selectivity. A series of mixed copper–cobalt metal spinel oxides（Cu_xCo_yO_z）doped with graphene oxide thin films were deposited on commercial grade aluminium substrates using a sol-gel dip-coating technique at an annealing temperature of 500 °C in air for 1 h. Characterizations of the synthesized films were carried out by high temperature synchrotron radiation X-ray Diffraction（SRXRD）, UV–Vis, Fourier Transform infrared spectroscopy（FTIR） and X-ray photoelectron microscopy（XPS）techniques. High thermal stability of coatings with multiple phases, binary and ternary metal oxides, was defined through SR-XRD study. FTIR analysis shows moderate（〈80%） to high（up to 99%） reflectance in the infrared region while the UV–Vis investigations demonstrate that, in the visible region, solar absorption increases gradually（up to 95%） with the addition of graphene oxide to the Cu_x Co_y O_z coatings.With the incorporation of 1.5 wt.% of graphene oxide to the copper–cobalt oxide coatings, a high solar selectivity of 29.01（the ratio of the average solar absorptance in visible and the average thermal emittance in infrared to far infrared region; α/ε） was achieved.