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With the rapid development of portable electronics, all-solid-state thin-film supercapacitors (ASSTFSs) have attracted tremendous attention and been considered as competitive candidates owing to their ultraflexibility and high safety. The major challenge in ASSTFSs is the low capacity and energy density due to the lack of proper electrode materials with high conductivity and surface area. In this study, we develop a nanocomposite electrode combined with pseudocapacitive vanadium pentoxide and highly conductive graphene with ultrathin thickness for the application of ASSTFSs. The novel structure of the nanocomposite achieves maximal integration of both the merits of each component with high conductivity and ultrathin thickness, which enhances the electron transfer, shortens the ion diffusion paths and increases the electrode-electrolyte contact in ASSTFSs, leading to high electrochemical performance. The as-fabricated ASSTFS achieves a high areal capacitance of 11718 μF cm-2, a remarkable energy density of 1.13 μW h cm-2 at a power density of 10.0 μW cm-2 and long-term cycling stability for 2000 cycles, demonstrating the superior electrochemical performance and rendering it a promising candidate for portable electronics. [ABSTRACT FROM AUTHOR]

Inorganic graphene analogues (IGAs) are currently in the spotlight of nanotechnology with the aim of achieving superior energy storage performance. However, cumbersome, expensive and time-consuming synthetic routes have definitely hindered further study of these species, thus the development of facile, low-cost and ultra-rapid synthetic approaches to these species is urgently needed and has met with limited success so far. Herein, we put forward an ultra-rapid, low-cost and facile microwave-assisted strategy to achieve this goal without exfoliation for the first time. This protocol relies on microwave dielectric heating, a reducing reagent and reactive medium, which will efficiently lower the Gibbs activation energy and polarize the conducting electrons. As an example, (001)-oriented ultrathin birnessite K0.17MnO2 nanosheets with a thickness of only 2 nm were successfully synthesized within 5 min, much faster than presently known routes. Notably, this novel route can also be extended to the synthesis of ultrathin Na-type birnessite nanosheets, revealing the universality of this synthetic strategy by extending to those layered compounds. The layered ultrathin birnessite K0.17MnO2 nanosheet-based electrode exhibits remarkably improved electrochemical characteristics compared with its bulk counterpart, showing a high specific capacitance of 206 F g−1 at 1 A g−1 and an excellent cycling performance at a large current density of 5 A g−1 (＞93% retention over 1000 cycles). Even in lithium ion battery cathodes, the reversible capacity of 167.4 mA h g−1 is still retained with a negligible capacity loss per cycle (0.25%), which is superior to most reported birnessite nanostructures, suggesting a remarkably promising candidate for energy storage. Such intriguing behavior is mainly attributed to the intrinsic crystal structure and the synergistic effect of IGAs, such as huge surface area, facile guest ion diffusion and electron transport. This work opens the door for the ultra-rapid and facile preparation of ultrathin nanosheets, which will significantly expand the studies of IGAs and optimize energy storage through rational materials design and synthesis. [ABSTRACT FROM AUTHOR]

Room-temperature ferromagnetic semiconductors (FSC) have attracted great interests and, in particular, their 1D nanostructures with the inherent high aspect ratio give them a unique advantage in establishing nanoscale spintronic devices. Herein, a facile hydrothermal approach has been developed to synthesise K2V6O16 ·1.5H2O superlong nanobelts, which were confirmed to be a new kind of room-temperature ferromagnetic semiconductors with a 1D nanostructure. The FSC material has a band gap of 1.95 eV and a coercivity of 67 Oe at 300 K, showing fascinating ferromagnetic behaviour in the semiconducting material. The formation mechanism of the K2V6O16 ·1.5H2O nanobelts was atomically known from the full embodiments of the internal bronze K2V6O16 ·1.5H2O structure. Moreover, density functional calculations and the corresponding experimental results clearly reveal the nature of the ferromagnetic behaviour, and we found that the oxygen vacancies produced during the solution growth process generate the spin orientations forming the room-temperature ferromagnetism. We believe these insights give a better understanding of the ferromagnetic mechanism in RTFM materials, and such superlong nanobelts pave a new way for fabricating fascinating spintronic nanodevices and nanosensors in the near future. [ABSTRACT FROM AUTHOR]

Despite the promising applications of copper selenide nanoparticles, an in-depth elucidation of the inherent properties of tetragonal Cu2Se (β-Cu2Se) has not been performed because of the lack of a facile synthesis on the nanoscale and an energy-intensive strategy is usually employed. In this work, a facile wet-chemical strategy, employing HCOOH as reducing agent, has been developed to access single-crystalline metastable β-Cu2Se hyperbranched architectures for the first time. The process avoids hazardous chemistry and high temperatures, and thus opens up a facile approach to the large-scale low-cost preparation of metastable β-Cu2Se hyperbranched architectures. A possible growth mechanism to explain the formation of the β-Cu2Se dendritic morphology has been proposed based on time-dependent shape evolution. Further investigations revealed that the metastable β-Cu2Se can convert into the thermodynamically more stable cubic α-Cu2− xSe maintaining the dendritic morphology. An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the β-Cu2Se hyperbranched structures, ultimately leading to solid-state phase conversion from β-Cu2Se into superionic conductor α-Cu1.8Se, which has potential applications in energy-related devices and sensors. [ABSTRACT FROM AUTHOR]

Despite the promising applications of copper selenide nanoparticles, an in-depth elucidation of the inherent properties of tetragonal Cu(2)Se (β-Cu(2)Se) has not been performed because of the lack of a facile synthesis on the nanoscale and an energy-intensive strategy is usually employed. In this work, a facile wet-chemical strategy, employing HCOOH as reducing agent, has been developed to access single-crystalline metastable β-Cu(2)Se hyperbranched architectures for the first time. The process avoids hazardous chemistry and high temperatures, and thus opens up a facile approach to the large-scale low-cost preparation of metastable β-Cu(2)Se hyperbranched architectures. A possible growth mechanism to explain the formation of the β-Cu(2)Se dendritic morphology has been proposed based on time-dependent shape evolution. Further investigations revealed that the metastable β-Cu(2)Se can convert into the thermodynamically more stable cubic α-Cu(2-x)Se maintaining the dendritic morphology. An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the β-Cu(2)Se hyperbranched structures, ultimately leading to solid-state phase conversion from β-Cu(2)Se into superionic conductor α-Cu(1.8)Se, which has potential applications in energy-related devices and sensors., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Although about 200,000 metric tons of gamma-MnO(2) are used annually worldwide for industrial applications, the gamma-MnO(2) structure is still known to possess a highly ambiguous crystal lattice. To better understand the gamma-MnO(2) atomic structure, hexagon-based nanoarchitectures were successfully synthesized and used to elucidate its internal structure for the present work. The structural analysis results, obtained from the hexagon-based nanoarchitectures, clearly show the coexistence of akhtenskite (epsilon-MnO(2)), pyrolusite (beta-MnO(2)), and ramsdellite in the so-called gamma-MnO(2) phase and verified the heterogeneous phase assembly of the gamma-MnO(2) state, which violates the well-known "De Wolff" model and derivative models, but partially accords with Heuer's results. Furthermore, heterogeneous gamma-MnO(2) assembly was found to be a metastable structure under hydrothermal conditions, and the individual components of the heterogeneous gamma-MnO(2) system have structural similarities and a high lattice matches with pyrolusite (beta-MnO(2)). The as-obtained gamma-MnO(2) nanoarchitectures are nontoxic and environmentally friendly, and the application of such nanoarchitectures as support matrices successfully mitigates the common problems for phase-change materials of inorganic salts, such as phase separation and supercooling-effects, thereby showing prospect in energy-saving applications in future "smart-house" systems.