An asymmetric supercapacitor based on controllable WO3 nanorod bundle and alfalfa-derived porous carbon.

A novel asymmetric supercapacitor (ASC) is assembled on the basis of an inerratic hexagonal-like WO3 nanorod bundle as a negative electrode and graphene-like alfalfa-derived porous activated carbon (APAC) as the positive electrode in 1 M H2SO4 aqueous electrolyte. The WO3 nanostructures prepared at pH of 1.6, 1.8, 2.0, 2.5 and 3.0 display hexagonal disc-like, nanorod bundle, inerratic hexagonal-like, sphere-like, and needle-shaped nanorod morphology. WO3-2.0, which was prepared at a pH of 2.0, exhibits high specific capacitance (415.3 F g-1 at 0.5 A g-1). APAC-2, which had the mass ratios of dried alfalfa and ZnCl2 as 1 : 2, showed a 3D porous structure, large surface area (1576.3 m2 g-1), high specific capacitance (262.1 F g-1 at 0.5 A g-1), good cycling stability with 96% of initial specific capacitance after 5000 consecutive cycles. The ASC assembled with WO3-2.0 and APAC-2 exhibits high energy density (27.3 W h kg-1 at a power density of 403.1 W kg-1), as well as good electrochemical stability (82.6% capacitance retention after 5000 cycles). Such outstanding electrochemical behavior implies that the electrode materials are promising for practical energy-storage systems.

Nanostructure selenium compounds as pseudocapacitive electrodes for high-performance asymmetric supercapacitor.

The electrochemical performance of an energy conversion and storage device like the supercapacitor mainly depends on the microstructure and morphology of the electrodes. In this paper, to improve the capacitance performance of the supercapacitor, the all-pseudocapacitive electrodes of lamella-like Bi18SeO29/BiSe as the negative electrode and flower-like Co0.85Se nanosheets as the positive electrode are synthesized by using a facile low-temperature one-step hydrothermal method. The microstructures and morphology of the electrode materials are carefully characterized, and the capacitance performances are also tested. The Bi18SeO29/BiSe and Co0.85Se have high specific capacitance (471.3 F g-1 and 255 F g-1 at 0.5 A g-1), high conductivity, outstanding cycling stability, as well as good rate capability. The assembled asymmetric supercapacitor completely based on the pseudocapacitive electrodes exhibits outstanding cycling stability (about 93% capacitance retention after 5000 cycles). Moreover, the devices exhibit high energy density of 24.2 Wh kg-1 at a power density of 871.2 W kg-1 in the voltage window of 0-1.6 V with 2 M KOH solution.