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Composite supercapacitive materials can combine two different kinds of electrode materials with different energy storage mechanisms, as well as present enhanced supercapacitive performance. In this paper, a reduced graphene oxide aerogel (GA) was prepared with an adjustable pore structure and used as a matrix for loading of secondary active material (MnO2) through an electrochemical deposition method. The influences of the deposition time and deposition voltage on the electrochemical behaviors and specific capacitances of MnO2/GA composites were studied. The unique three-dimensional porous structure of GA can act as a good matrix for MnO2. The results show that when the deposition time is 30 s and deposition voltage is 1.0 V, the MnO2/GA composite has the highest specific capacitance of 664 F/g at a current density of 1 A/g. Compared with neat GA, the specific capacitance of the MnO2/GA composite is enhanced by 190%, which can be assigned to the co-contribution of two kinds of active materials, a facile ion diffusion path through the porous structure, and good electron conductivity of the GA.

A Poly (3, 4-dioxyethylthiophene)–Carbon Nanotubes (PEDOT–CNT) composite electrochromic material, connected by interfacial covalent bonds, was successfully synthesized by electrochemical copolymerization of 3, 4-dioxyethylthiophene with thiophene-2-methylamine functionalized CNT. The molecular and aggregate structures of PEDOT–CNT were investigated by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The electrochemical behavior and electrochromic properties of PEDOT–CNT were measured by CV (cyclic voltammetry), UV–Vis (ultraviolet visible spectroscopy) and EIS (electrochemical impedance spectroscopy). The test results show that the electrochromic performance of PEDOT–CNT is better than that of neat PEDOT. As the percentage of carbon nanotubes increases, the contrast and response speed of the composites increase accordingly. The PEDOT film has a contrast under square-wave potential of 0.54, a coloring time of 6.42 s, and a fading time of 2.54 s. Compared with PEDOT, the contrasts of PEDOT–CNT-3%, PEDOT–CNT-5% and PEDOT–CNT-7% are increased by 31%, 33%, and 89%, respectively. The response speeds of PEDOT–CNT-5% increase to coloring time of 3.51 s and fading time of 1.37 s.

Polyaniline nanotubes (PANI-T) and graphene oxide (GO) have been compounded by a postcomposition method with the assistance of electrostatic adsorption. Using this so-called postcomposition method, both the electric double-layer capacitance of the GO and the pseudocapacitance of the conducting polymer can be utilized. PANI-T prepared by a rapid mixing method was positively charged by pretreatment with (3-aminopropyl)triethoxysilane (APTES). PANI/GO composites were obtained by mixing the positively charged PANI-T and negatively charge GO with the assistance of electrostatic attraction. Charge–discharge measurements in 1 mol L−1 H2SO4 aqueous electrolyte revealed that the specific capacitance of PANI-T/GO-10% could reach 1220 F g−1 at a current density of 0.5 A g−1, being much higher than the value of 648 F g−1 for PANI-T. After 500 cycles of charge–discharge testing, the composite retained 97% of its capacitance. These enhanced supercapacitive properties can be attributed to the two types of energy storage mechanism and the electrostatic interaction between GO and PANI-T. Preparation of such PANI-T/GO composite electrode materials by electrostatic adsorption thus provides an efficient approach for improvement of the supercapacitive properties of conducting polymers or metal oxides.

In this article, polyaniline nanofibers (PANI-NF)/manganese dioxide composites (PANI/MnO2) were synthesized through an interfacial polymerization approach. The PANI-NF and MnO2 were obtained by in situ oxidation of aniline by potassium permanganate and in situ reduction of potassium permanganate by aniline, respectively. During the interfacial polymerization, the monomer aniline can only be oxidized to PANI after it diffuses into the water phase. This diffusion-control feeding process of the monomer results in nanofiber structure. The morphologies and crystal structures of the prepared PANI/MnO2 composites were measured by scanning electron microscopy and x-ray diffraction. The supercapacitive behaviours of these composites were analysed by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests. The CV and GCD tests indicate that the PANI/MnO2 composites possess better electrochemical activity and higher capacitive properties compared to neat PANI nanofibers. The specific capacitance of PANI/MnO2 composites and PANI-NF are 751 F g−1 and 180 F g−1 at 0.2 A g−1 in Na2SO4 solution, respectively. We believe that the enhanced capacitive properties are related to the special nanostructure and strong interaction between PANI and MnO2 that resulted from the interfacial synthesis method.

In this article, we reported a biomass carbon/MnO2 nanocomposite electrode material prepared by a hydrothermal method. Sugarcane bagasse and KOH were the carbon source and activation agent, respectively. The obtained sugarcane bagasse carbon is rich in pore structure, so it can act as the host for MnO2. The biomass carbon/MnO2 nanocomposite electrode was prepared by a hydrothermal method. The morphologies of materials were observed by scanning electron microscopy. Raman spectra and x-ray diffraction were utilized to characterize the molecular and crystal structures of samples, respectively. The electrochemical and capacitive performances of materials were tested by electrochemical workstation. By calculation, the specific capacitance of sugarcane bagasse carbon, MnO2 and composite electrode are 280 F g−1, 163 F g−1 and 359 F g−1, respectively. Compared with pure sugarcane bagasse carbon and MnO2, the specific capacitance of the composite increases by 28% and 120%, respectively. After 2000 cycles of charge and discharge, the capacitance retention of the composite is 94%, which is higher than 91% of sugarcane bagasse carbon and 45% of MnO2.

A novel ferrocene-containing hybrid electrochromic material was synthesized via copolymerization of aniline with p-phenylenediamine functionalized acetyl ferrocene in the presence of poly (styrene sulfonate) dopant in an aqueous medium, and neat polyaniline (PANI) was prepared for comparison. The polymerization characteristics and the structure of the copolymer were systematically studied by Fourier-transform infrared, meanwhile, their electrochromic properties and electrochemical behaviors were tested by UV–vis spectra, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). It was found that the strong covalent bond and large conjugated system between PANI and ferrocene enhance the electron transfer rate and electron delocalization in the ferrocene-polyaniline (Fc-PANI) hybrid. In particular, the electrochromic device with Fc-PANI as the active layer shows significant enhancement in optical contrast over the PANI-based device.

The molecular architecture of conducting polymers has a significant impact on their conjugated structure and electrochemical properties. We have investigated the influence of star-shaped structure on the electrochemical and electrochromic properties of polyaniline (PANI). Star-shaped PANI (SPANI) was prepared by copolymerization of aniline with triphenylamine (TPA) using an emulsion polymerization method. With addition of less than 4.0 mol.% TPA, the resulting SPANI exhibited good solubility in xylene with dodecylbenzenesulfonic acid (DBSA) as doping acid. The structure and thermal stability of the SPANI were characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis, and the electrochemical behavior was analyzed by cyclic voltammetry (CV). The electrochromic properties of SPANI were tested using an electrochemical workstation combined with an ultraviolet–visible (UV–Vis) spectrometer. The results show that, with increasing TPA loading, the thermal stability of SPANI increased. With addition of 4.0 mol.% TPA, the weight loss of SPANI was 36.9% at 700°C, much lower than the value of 71.2% for PANI at the same temperature. The low oxidation potential and large enclosed area of the CV curves indicate that SPANI possesses higher electrochemical activity than PANI. Enhanced electrochromic properties including higher optical contrast and better electrochromic stability of SPANI were also obtained. SPANI with 1.6 mol.% TPA loading exhibited the highest optical contrast of 0.71, higher than the values of 0.58 for PANI, 0.66 for SPANI-0.4%, or 0.63 for SPANI-4.0%. Overdosing of TPA resulted in slow switching speed due to slow ion transport in short branched chains of star-shaped PANI electrochromic material. Long-term stability testing confirmed that all the SPANI-based devices exhibited better stability than the PANI-based device.