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Highlights: [•] Ni(OH)2/vertically oriented graphene nanosheets (V-GNs) was prepared. [•] Ni(OH)2/V-GNs had enhanced specific capacitance, cycling reversibility and stability. [•] Performance of Ni(OH)2/GNs/NF-AC asymmetric supercapacitor was studied. [ABSTRACT FROM AUTHOR]

Abstract: A convenient and efficient preparation method for separation graphene oxide with well-defined size distribution is developed using a centrifugation technique. The graded profile of graphene oxide nanosheets with narrow size distribution is effectively controlled by varying the centrifugation speed. The results show that the oxygen content of graphene oxide is highly dependent on their size distribution. Graphene oxide nanosheet with large size shows a red-shift in UV–vis absorption spectra, compared to graphene oxide with small size. This phenomenon is interpretation by a density functional theory calculation. The present work will provide a simple method to prepare graphene oxide nanosheets with controllable size distribution and C/O ratio, which will be valuable for the functionalization of graphene-based hybrids and the fabrication of graphene nano-devices. [Copyright &y& Elsevier]

Abstract: Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO3)2 aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)2 has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg−1 at current density of 2 and 32 Ag−1, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag−1, which is higher than that of Co(OH)2/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)2 and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes. [Copyright &y& Elsevier]

Perovskites are solution-processed, high-performance semiconductors of interest in low-cost photovoltaics. The interfaces between the perovskite photoactive layers and the top and bottom contacts are crucial for efficient charge transport and minimizing trapping. Control of the collection of charge carriers at these interfaces is decisive to device performance. Here, we review recent progress in the realization of efficient perovskite solar cells using cheap, easily processed, stable, carbon-based interlayers. Interface materials including graphene, carbon nanotubes, fullerenes, graphene quantum dots and carbon dots are introduced and their influence on device performance is discussed. • The use of carbon nanomaterials in perovskite photovoltaic devices is reviewed. • Carbon nanomaterials allow precision tuning of their properties to serve as both electron- and hole-transporting material. • Carbon nanomaterials facilitate an optimized charge balance, device stability, and efficiency. [ABSTRACT FROM AUTHOR]