关键词: 二氧化锰, 碳纳米管, 三明治结构, 复合物, 扩散, 电化学, 超级电容器

Abstract:

MnO₂ is regarded as the most attractive electrode material for supercapacitor (SC) because of its low cost and non-toxic nature, high natural abundance, and superb theoretical specific capacitance. The tantalum capacitor electrode material MnO₂ still has a problem of poor conductivity and easy peeling during charging and discharging. In this study, a sandwich MnO₂/CNTs/MnO₂ mesoporous composite is fabricated by a facile galvanostatic electrochemical deposition approach on the surface of carbon paper pre-oxidized by nitric acid, and the middle layer of CNTs was added by a simple smear-drying method. The crystal structure, surface morphology and pore characteristics of the sandwich composite are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption test. The prepared composite shows a sandwich structure with mesopores of about 5 nm, which could ensure the efficient diffusion of electrolyte ions. Three-dimensional carbon paper could provide abundant conductive sites for attachment of MnO₂. The synthesized α-MnO₂ has a fluffy and porous morphology, which could reduce the expansion stress of the composite effectively. The intermediate layer of carbon nanotubes (CNTs) serve as conductive media relay between the inner and outer layers of MnO₂ to further improve the conductivity of composite. The composite exhibits excellent electrochemical performance: the electrode has a reversible specific capacity of 428.8 F·g^-1 at a current density of 0.1 A·g^-1 and an outstanding specific capacitance retention of ca. 80% at 5 A·g^-1. Moreover, the electrode still has an excellent cycle stability (95% retention rate) at a current density of 1 A·g^-1 after 6000 cycles.

Key words: manganese dioxide, carbon nanotube, sandwich structure, composites, diffusion, electrochemical, supercapacitor