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

Abstract

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.