Free-Standing3D Polyaniline-CNTs/Ni-fiber Hybrid Electrodes For High-Performance Supercapacitors

Rencently, hybrid material made by electronic conducting polyaniline (PANi) and carbon nanotubes (CNTs) is an emerging class of electrode materials with great potential applications such as supercapacitors. However, the bottleneck from its powder-molding has restricted its applications in electrochemistry. Accordingly, development of new method for macroscopic fabrication of PANi/CNTs composites is the key to solve this problem.In this paper, a new-type free-standing3D macroscopic PANi-CNTs/Ni-fiber has been developed for high-performance supercapacitors. A CNTs/Ni-fiber paper with characteristic irregular3D networks and a thin-sheet structure was obtained firstly through direct growth of CNTs on a sinter-locked Ni-microfibrous structure (consisting of5vol%8-μm Ni fibers and95vol%voidage) via catalytic chemical vapor deposition (CCVD) method. Afterwards, the PANi was assembled onto the CNTs rooted on the Ni-microfibrous matrix by sol coating method. This novel approach permits the desirable large-area fabrication and provides a unique combination of high PANi loading, binder-free feature, excellent electrical conductivity, open macro-/meso-porous structure and high accessibility. In the as-prepared hybrid electrodes, the Ni-fiber network serves as current collector and the CNTs grown on the Ni-fiber act as nano conducting wire to link the charge-storage PANi with charge-transfer promotion.The studies on electrochemical performances of the samples as supercapacitor electrodes were carried out in1.0mol L-1Na2SO4aqueous electrolyte by means of cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy. The representative hybrid electrode consisting of28wt%PANi (PANi with molecular weight of10000is used for sol-coating) and28wt%CNTs with44wt%Ni-fiber in balance (the CNTs/Ni-fiber) delivered very high specific capacitances (e.g.,1450F g-1according to the PANi weight,725F g-1 according to the weight of PANi and CNTs, or409F g-1according to the whole electrode weight at the current density of0.5A g-1) and large energy density (e.g.,-22Wh kg-1at～2000W kg-1or～38Wh kg-1at200W kg-1on the basis of total electrode mass) with good electrochemical cyclability (over70%of the original specific capacitance could be retained after300cycles and then lasted over1000cycles). The FT-IR. spectra indicated that a strong π-π interaction took place between the backbone structure of PANi and CNT surface and thereby promoting and/or stabilizing the quinoidal ring structure, this kind of effect can not only enhance the conductivity of the hybrid material, but also as a result of promoting "charge-transfer" effect between PANi and CNTs.