Polyanilene-Coated Porous Carbon Nanofiber Electrodes for Supercapacitors

We report the development of three-dimensional hybrid supercapacitor electrodes combining pseudocapacitive polyanilene and porous carbon nanofibers. The porous carbon nanofibers with specific surface area of  >1500 m²/g were first fabricated via electrospinning of a blend of carbon precursor and sacrificial polymer followed by high temperature pyrolysis. The pyrolysis step converted the carbon precursor (polyacrylonitrile-PAN) to carbon and decomposed out the sacrificial polymer forming micro/mesopores within carbon nanofibers. Figure 1 shows the SEM images of porous carbon nanofibers fabricated using different PAN concentrations. Figure 2 shows the CV curves  (in 1M H₂SO₄) of porous carbon nanofibers fabricated using 40 wt% PAN at various scan rates exhibiting ideal rectangular shape indicative of fast ion transport and high power handling capability. Polyanilene was conformally coated on porous carbon nanofiber substrates via electropolymerization of aniline monomer in 1 M H₂SO₄to develop device-ready freestanding hybrid electrodes. Electropolymerization was carried out in a three-electrode setup using the potentiodynamic method with Ag/AgCl as the reference electrode and platinum mesh as the counter electrode. Figure 3 provides an SEM image showing conformal coating of polyanilene over porous carbon nanofibers. Electrochemical characterization of the hybrid polyanilene/porous carbon nanofiber samples was conducted. Figure 4 shows the CV curve of the hybrid electrodes with 10 wt% polyanilene. CV shows clear polyanilene redox peaks exhibiting transformation from fully reduced leucoemeraldine to half oxidized emeraldine form. CV shows clear retention of electric double layer capacitance in the hybrid electrodes resulting in a total specific capacitance of over 250 F/g based on the weight of the complete electrode (porous carbon substrate and polyanilene).

Figure Captions

Figure 1: SEM images of mesoporous carbon nanofibers fabricated via high temperature calcination of the nanofibers electrospun using different material compositions generating different intra-fiber pore sizes. Scale bars = 500 nm. All samples exhibit >1500 m²/g specific surface area as measured using nitrogen physisorption (not shown).

Figure 2. Cyclic voltammetry  curve of porous carbon nanofibers at various scan rates in 1M H₂SO_4.

Figure 3. SEM image of 10 wt% polyanilene conformally coated over porous carbon nanofibers.

Figure 4. Cyclic voltammetry curve of 10 wt% polyanilene coated over porous carbon nanofibers at 20 mV/s in 1M H₂SO_4.