The intercalation of large organic ammonium ions (tetramethylammonium ions (TMA + ), tetraethylammonium ions (TEA + ), tetrapropylammonium ions (TPA + ), and tetrabutylammonium ions (TBA + )) into layered graphite oxide (GO) was systematically investigated. The intercalation reactions were completed at 25 °C after 3 days, and stable colloidal suspensions were obtained at TAAl/Hs ) 5 (molar ratio of tetraalkylammonium ions (TAA + ) over exchangeable protons in GO). The sediments after centrifuging the colloidal suspensions showed amorphous phase X-ray diffraction patterns, indicating that exfoliation of the layered structure into nanosheets took place in the suspension. When the sediments were dried at 70 °C for 3 days, layered structures of TAA + -intercalated GO materials with basal spacings of 1.56, 1.67, 1.84, and 2.37 nm, respectively, appeared. The basal spacing of the layered compounds decreased with a decrease of relative humidity during drying. When the dried TAA + -intercalated GO compounds were exposed to a humid saturated atmosphere, the basal spacing increased gradually, finally becoming an amorphous structure. The maximum saturation of intercalated TAA + ions into GO decreased with the increase in alkyl chain length. When the TAA + -intercalated materials were washed with distilled water and acid-treated, a process of deintercalation of TAA + ions from the interlayer occurred. A schematic model for the deintercalation-intercalation involving a exfoliation process is proposed. The layered structure of TAA +intercalated GO materials is discussed in terms of the dimension of the GO layer and the sizes of H2O molecules and TAA + ions.

Anisotropic 2D layered material rhenium disulfide (ReS2 ) with high crystal quality and uniform monolayer thickness is synthesized by using tellurium-assisted epitaxial growth on mica substrate. Benefit from the lower eutectic temperature of rhenium-tellurium binary eutectic, ReS2 can grow from rhenium (melting point at 3180 °C) and sulfur precursors in the temperature range of 460-900 °C with high efficiency.

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By using three-dimensional (3D) tubular molybdenum disulfide (MoS2) as both an active material in electrochemical reaction and a framework to provide more paths for insertion and extraction of ions, PANI nanowire arrays with a diameter of 10-20 nm can be controllably grown on both the external and internal surface of 3D tubular MoS2 by in situ oxidative polymerization of aniline monomers and 3D tubular MoS2/PANI hybrid materials with different amounts of PANI are prepared. A controllable growth of PANI nanowire arrays on the tubular MoS2 surface provides an opportunity to optimize the capacitive performance of the obtained electrodes. When the loading amount of PANI is 60%, the obtained MoS2/PANI-60 hybrid electrode not only shows a high specific capacitance of 552 F/g at a current density of 0.5 A/g, but also gives excellent rate capability of 82% from 0.5 to 30 A/g. The remarkable rate performance can be mainly attributed to the architecture with synergistic effect between 3D tubular MoS2 and PANI nanowire arrays. Moreover, the MoS2/PANI-60 based symmetric supercapacitor also exhibits the excellent rate performance and good cycling stability. The specific capacitance based on the total mass of the two electrodes is 124 F/g at a current density of 1 A/g and 79% of its initial capacitance is remained after 6000 cycles. The 3D tubular structure provides a good and favorable method for improving the capacitance retention of PANI electrode.

A flexible carbon fiber aerogel with a very high surface area for supercapacitor application is reported by carbonization and chemical activation of low-cost natural cotton with KOH. The carbon fibers in the aerogel present as a twisted and tubular structure. Depending on the amount of KOH used in the activation process, the specific surface area of aerogels ranges from 1536 to 2436 m2 g–1, while their electrical conductivity remains ∼860 S m–1. In spite of pore size in the range of 1.0–4.0 nm and pore volume mainly contributed by micropores, the carbon aerogel exhibits a high specific capacitance of 283 F g–1 (1 A g–1) in 6 M KOH aqueous electrolyte and retains a high capacitance retention of 224 F g–1 at current density up to 100 A g–1. Importantly, a symmetric capacitor built with the aerogel electrodes exhibits a rather small time constant (0.56 s). The superior capacitive performance of a CF electrode is closely related to its distinct structural advantage. The tubular carbon fibers that are several millimeters in length offer ultralong electronic and ionic pathways, while plenty of nanopores on the fiber walls created by KOH activation enable fast ion transport across the walls. Our results demonstrate that capacitive performance of the traditional microporous carbon, which is characterized by poor ion kinetics, can be significantly enhanced by properly engineering the electrode architecture.

We report in this paper the studies on protonation, exfoliation, and self-assembly of birnessite-type manganese oxide single crystals. The protonation was carried out by extracting K + ions from the potassium manganese oxide single crystals in a (NH 4 ) 2 S 2 O 8 aqueous solution heated at 60 °C, exfoliation to nanosheets by the intercalation of TMA + ions followed by water-washing, and the self-assembly of MnO 2 nanosheets in a dilute NaCl solution. The structures of the samples at these stages were systematically investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, and chemical compositional analysis. Electron density distribution in the protonated single crystal was visualized by whole-pattern fitting based on the maximum entropy method. The results indicated that the protonated single crystals can be exfoliated to MnO 2 unilamellar nanosheets. The selfassembly yields layered crystals with basal spacing of 0.72 nm and with a composition of H 0.18 Na 0.089 MnO 2 ‚0.47H 2 O. The layered crystals had a textured polycrystalline structure, where c-axes of the nanosheets aligning along a certain direction constitute a fiber axis with azimuthal orientations of a-or b-axes about the fiber axis. Moreover, the azimuthal orientations of a-or b-axes are probably arranged at particular angles to one another, rather than randomly. The mean oxidation state of manganese exhibits no marked change at the various stages of the protonation, exfoliation, and self-assembly.

A graphene-based supercapacitor electrode suitable for ionic liquid electrolytes was designed and prepared based on the electrostatic interactions between negatively charged graphene oxides (GO) and positively charged mesoporous carbon CMK-5 platelets. Thermal annealing of the GO-CMK-5 composite under an inert atmosphere yielded a hierarchical carbon nanostructure with CMK-5 platelets uniformly intercalated between the GO sheets. The electrochemical results demonstrated that the CMK-5 platelets with straight and short mesochannels served as a highway for the fast transport of electrolyte ions, while the separated graphene sheets with more exposed electrochemical surface area favored the formation of electrical double layer capacitance. The RGO-CMK-5 electrode exhibited a specific capacitance of 144.4 F g À1 in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid electrolyte, which can be charged/discharged at an operating voltage of 3.5 V. As a result, an energy density of 60.7 W h kg À1 and a power density as high as 10 kW kg À1 were achieved, which outperforms most of the present graphene-based supercapacitors. Moreover, the superior rate performance together with the excellent cycle performance makes the RGO-CMK-5 composite a promising candidate for next generation supercapacitor electrodes.

The phase transition behavior and piezoelectric properties of (Ba1−xCax)(Zr0.1Ti0.9)O3 and (Ba0.85Ca0.15)(ZryTi1−y)O3 ceramics were investigated in this work to find out the potential factors contributing to large piezoelectricity. It was found that the morphotropic phase boundary (MPB) of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics was closely related to the presence of an intermediate phase (considered as orthorhombic phase in this work) between rhombohedral (R) and tetragonal (T) phases at a narrow region, which could be carefully adjusted by the temperature and contents of Ca and Zr in the composition. In addition, the maximum piezoelectric and electromechanical coupling coefficients (with d33 = 572 pC/N and kp = 0.57) were observed near the MPB region close to T phase side, which might be intimately related to the presence of the intermediate phase. This investigation yielded a new sight to understand the mechanism of enhanced piezoelectricity near the MPB.