High-quality graphene scrolls (GSS) with a unique scrolled topography are designed using a microexplosion method. Their capacitance properties are investigated by cyclic voltammetry, galvanostatic charge-discharge and electrical impedance spectroscopy. Compared with the specific capacity of 110 F g(-1) for graphene sheets, a remarkable capacity of 162.2 F g(-1) is obtained at the current density of 1.0 A g(-1) in 6 M KOH aqueous solution owing to the unique scrolled structure of GSS. The capacity value is increased by about 50% only because of the topological change of graphene sheets. Meanwhile, GSS exhibit excellent long-term cycling stability along with 96.8% retained after 1000 cycles at 1.0 A g(-1). These encouraging results indicate that GSS based on the topological structure of graphene sheets are a kind of promising material for supercapacitors.
High‐quality graphene scrolls with several possible conformations are designed using a facile microexplosion method under an ultrasonic reaction between MnO2 and H2O2. The as‐obtained graphene scrolls exhibit a tubular structure. The methodology successfully realizes the transformation from a 2D material to a nearly 1D material.
Anatase hierarchical TiO2 with innovative designs (hollow microspheres with exposed high-energy {001} crystal facets, hollow microspheres without {001} crystal facets, and solid microspheres without {001} crystal facets) were synthesized via a one-pot hydrothermal method and characterized. Based on these materials, gas sensors were fabricated and used for gas-sensing tests. It was found that the sensor based on hierarchical TiO2 hollow microspheres with exposed high-energy {001} crystal facets exhibited enhanced acetone sensing properties compared to the sensors based on the other two materials due to the exposing of high-energy {001} crystal facets and special hierarchical hollow structure. First-principle calculations were performed to illustrate the sensing mechanism, which suggested that the adsorption process of acetone molecule on TiO2 surface was spontaneous, and the adsorption on high-energy {001} crystal facets would be more stable than that on the normally exposed {101} crystal facets. Further characterization indicated that the {001} surface was highly reactive for the adsorption of active oxygen species, which was also responsible for the enhanced sensing performance. The present studies revealed the crystal-facets-dependent gas-sensing properties of TiO2 and provided a new insight into improving the gas sensing performance by designing hierarchical hollow structure with special-crystal-facets exposure.
A reduced graphene oxide-poly(p-phenylenediamine) (RGO-PPD) composite was prepared from p-phenylenediamine (PD) and chlorinated graphene oxide (GO-COCl) sheets through amidation and polymerization processes. Then the RGO-PPD composite was characterized by using scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The results show that PPD nanoparticles were wrapped within or on the surface of graphene sheets uniformly. The RGO-PPD composite displayed a layered-stacking structure and had a large surface area (674.22 m 2 g À1 ) and a high pore volume (0.43 cm 3 g À1 ). Capacitive properties of the RGO-PPD composite were studied using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) in an electrolyte of 0.5 M H 2 SO 4 aqueous solution. The RGO-PPD exhibits a high specific capacitance of 347 F g À1 at a discharge rate of 1 A g À1 and excellent cycling stability with 90.1% of its initial capacitance at a large current density of 10 A g À1 after 1000 charge/discharge cycles. The energy density and specific power density of the present supercapacitor are 48.2 W h kg À1 and 1.0 kW kg À1 , respectively. The results suggest that the RGO-PPD is a promising material for high-performance supercapacitor applications.
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