Use of surfactant in aniline polymerization with TiO2 to PANI-TiO2 for supercapacitor performance

Polyaniline sulphate salt titanium dioxide composite (PANI-H2SO4 center dot TiO2) was synthesized by chemical in situ polymerization of aniline in the presence of TiO2. The effect of anionic surfactant (sodium lauryl sulphate) in this reaction was also assessed. During the polymerization reaction, sodium lauryl sulphate (SLS) is converted to dodecyl hydrogen sulphate (DHS) in the presence of acidic medium and gets doped onto polyaniline along with sulphuric acid dopant, i.e. formation of polyaniline-sulphate-dodecyl hydrogen sulphate-titanium dioxide composite (PANI-H2SO4-DHS center dot TiO2). In the PANI-H2SO4-DHS center dot TiO2 composite, the presence of DHS is confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray analysis (EDAX) and TiO2 is confirmed by XRD and EDAX results. In PANI-H2SO4-DHS center dot TiO2 system, the nanoparticle of TiO2 (10-20 nm) is uniformly embedded on nanofibres (20-60 nm) of PANI-H2SO4-DHS, and some part of PANI-H2SO4-DHS center dot TiO2 forms core-shell morphology, wherein TiO2 is in core and PANI-H2SO4-DHS in shell forms. Stability of PANI-H2SO4-DHS increases due to the incorporation of stable TiO2. Utility of PANI-TiO2 composite was carried out in supercapacitor cell system by performing cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopic techniques in 1 M H2SO4 solution. Very low values of solution resistance, charge transfer resistance and time constant are obtained between 0.2 and 0.6 V. Initial specific capacitance values for the cell carried out at low and high current densities are found to be 280 and 205 F g(-1), respectively, and after 1,700 charge-discharge cycles, its retention in the specific capacitance values is found to be the same (65-66 %) with coulombic efficiency of 98-100 %. A capacitor can work even at a high discharge rate. The efficiency of oxidizing and doping power increases with the use of a surfactant. Moreover, the use of a long chain surfactant dopant containing polyaniline as an electrode material plays an important role to increase the performance of the supercapacitor by allowing the electrolyte to easily enter and come out from PANI electrodes.