Ongoing technological advances in diverse fields including portable electronics, transportation, and green energy are often hindered by the insufficient capability of energy-storage devices. By taking advantage of two different electrode materials, asymmetric supercapacitors can extend their operating voltage window beyond the thermodynamic decomposition voltage of electrolytes while enabling a solution to the energy storage limitations of symmetric supercapacitors. This review provides comprehensive knowledge to this field. We first look at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area. Then we move to the recent progress made for the design and fabrication of electrode materials and the overall structure of asymmetric supercapacitors in different categories. We also highlight several key scientific challenges and present our perspectives on enhancing the electrochemical performance of future asymmetric supercapacitors.

The demand for flexible/wearable electronic devices that have aesthetic appeal and multi-functionality has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility. After a brief introduction to flexible supercapacitors, we summarize current progress made with graphene-based electrodes. Two recently proposed prototypes for flexible supercapacitors, known as micro-supercapacitors and fiber-type supercapacitors, are then discussed. We also present our perspective on the development of graphene-based electrodes for flexible supercapacitors.

3D cellular graphene films with open porosity, high electrical conductivity, and good tensile strength, can be synthesized by a method combining freeze-casting and filtration. The resulting supercapacitors based on 3D porous reduced graphene oxide (RGO) film exhibit extremely high specific power densities and high energy densities. The fabrication process provides an effective means for controlling the pore size, electronic conductivity, and loading mass of the electrode materials, toward devices with high energy-storage performance.

No abstract

Solution-grown films of CsPbBr nanocrystals imbedded in Cs PbBr are incorporated as the recombination layer in light-emitting diode (LED) structures. The kinetics at high carrier density of pure (extended) CsPbBr and the nanoinclusion composite are measured and analyzed, indicating second-order kinetics in extended and mainly first-order kinetics in the confined CsPbBr , respectively. Analysis of absorption strength of this all-perovskite, all-inorganic imbedded nanocrystal composite relative to pure CsPbBr indicates enhanced oscillator strength consistent with earlier published attribution of the sub-nanosecond exciton radiative lifetime in nanoprecipitates of CsPbBr in melt-grown CsBr host crystals and CsPbBr evaporated films.

Vigorous mixing of an aqueous particle dispersion with oil usually produces a particle-stabilized emulsion (a "Pickering emulsion"), the longevity of which depends on the particles' wetting properties. A known exception occurs when particles fail to adsorb to the oil-water interface created during mixing because of a strong repulsion between charges on the particle surface and similar charges on the oil-water interface; in this case, no Pickering emulsion is formed. Here, we present experimental evidence that the rarely considered electrostatic image force can cause a much bigger hindrance to particle adsorption and prevent the formation of Pickering emulsions even when the particle interaction with the interface charge is attractive. A simple theoretical estimate confirms the observed magnitude of this effect and points at an important limitation of Pickering emulsification, a technology with widespread industrial applications and increasing popularity in materials research and development.

Quasi-solid-state micro-supercapacitors with cellular graphene film as the active material and polyvinyl alcohol/H3PO4as the gel electrolyte have been fabricated. The 3D porous graphene films not only serve as high performance supercapacitor electrodes, but also provide an abundant ion reservoir for the gel electrolyte.

We demonstrate a simple method for preparing flexible, free-standing, three-dimensional porous graphene/MnO 2 nanorod and graphene/Ag hybrid thin-film electrodes using a filtration assembly process. These graphene hybrid films, which accelerate ion and electron transport by providing lower ion-transport resistances and shorter diffusion-distances, exhibit high specific capacitances and power performances, and excellent mechanical flexibility. A novel asymmetric supercapacitor (SC) has been fabricated by using a graphene/MnO 2 nanorod thin film as the positive electrode and a graphene/Ag thin film as the negative electrode. These devices exhibit a maximum energy density of 50.8 W h kg À1 and present a high power density of 90.3 kW kg À1 , even at an energy density of 7.53 W h kg À1 . The bent hybrid nanostructured asymmetric SC is connected to spin a fan, which also proved the high power density of the fabricated asymmetric SCs. These results suggest that such asymmetric graphene/ MnO 2 nanorod and graphene/Ag hybrid thin-film architectures are promising for next-generation highperformance flexible supercapacitors.