•Preparing three PANI nanostructures in HCl, H2SO4, and HNO3 reaction media during a slow interfacial polymerization.•Obtaining nanofibrous, nanogranular and hollow ball–like morphologies in the order of oxidizability of acids.•Demonstrating high specific capacitance, good rate performance and long cycle life of PANI nanofibers.Three nanostructured polyanilines (PANIs) were prepared by interfacial polymerization using different inorganic acids including HCl, H2SO4, and HNO3 as reaction media, respectively. The morphology-dependent structure and properties of as-prepared PANIs were characterized by means of scanning electron microscope, ultraviolet-visible spectra, Fourier transform infrared spectroscopy and X-ray diffraction patterns. Meanwhile, the electrochemical performance of the fabricated electrodes was evaluated by cyclic voltammetry, galvanostatic charge/discharge measurement, and electrochemical impedance spectroscopy. It is found that the reaction medium plays a vital role in deciding the final morphology and structure of product when a slow reaction rate occurred in interfacial polymerization. The as-prepared PANIs exhibited nanofibrous, nanogranular and hollow ball-like morphologies according to the order of the relative oxidizing ability of HCl < H2SO4 < HNO3, respectively. Furthermore, the capacitive properties of these composites as electrode materials highly depended not only on their morphologies but also on the conductivity, crystalline property and the inhibitory role of the lattice during the redox process, as well as the interparticle contact resistance. It is demonstrated that PANI nanofibers prepared in HCl medium exhibited high specific capacitance, good rate performance and long cycle life for the supercapacitor application.

Three kinds of nanostructured polyanilines (PANIs) were prepared through interfacial polymerization by using ammonium persulfate (APS) as a single oxidant, and APS/FeCl3, APS/K2Cr2O7 as composite oxidants, respectively. It is observed that faster formation process and higher yield of nanostructured PANIs could be achieved in the presence of FeCl3 and K2Cr2O7. The as-prepared PANIs were characterized by field emission scanning electron microscopy, ultraviolet–visible absorption spectroscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction analysis and electrochemical measurements including cyclic voltammetry and galvanostatic charge/discharge measurement. The influence of composite oxidants on the morphology, microstructure, and electrical and electrochemical properties of PANIs was discussed. Interestingly, when APS/K2Cr2O7 was used as the composite oxidants, PANI exhibited petal-like structure with high yield of 57.35% instead of general nanofibrous morphology formed in interfacial polymerization. Compared with those nanofibrous PANIs obtained by using APS as a single oxidant or APS/FeCl3 as composite oxidants, petal-like PANIs exhibited the largest specific capacitance (692.4 F/g at scan rate of 5 mV/s) and highest cycle stability among them. It provides a new insight into the control of PANI nanostructures with high yield and energy storage ability by simply selecting suitable composite oxidants in interfacial polymerization.