## 4 Properties and Applications of Synthesized Polymers with AAO Templates
### Energy, Sensing and Electronic Applications  
Supercapacitors are a class of energy-storage device that exhibit high power density (as compared to regular batteries) and large energy density (as compared to regular capacitors). Supercapacitors strongly benefit from the increase of the interface area between the electrolyte and the electrode, as this enhances the charge storage capability and the charge-discharge rates. Therefore, materials systems with large specific surface areas, such as nanowires arrays (once released from the AAO template), have attracted significant attention for electrode construction in supercapacitors. Polymers which are \(\pi\)-conjugated are the preferred polymeric choice for the preparation of electrodes in supercapacitors owing to their different redox states. For example, [PERSON] et al. grew polyaniline nanowires with various morphologies by changing the concentration of supporting electrolyte and the monomer, the potential of electropolymerization, and the polymerization time [149]. They observed that the increase of the sulfuric acid concentration during growth induced a transition from solid nanowires with tubular nanostructures, also finding a clear correlation between the electrochemical capacitance of the nanostructures and their morphology. Strikingly, they obtained a specific capacitance value of 700 F/g (measured at a charge/discharge rate of 5 A/g) for nanowires grown at 0.5 M aniline concentration. [PERSON] et al. [111] fabricated a symmetric supercapacitor employing electrochemically grown poly(3,4-ethylenedioxythiophene) (PEDOT) nanotube electrodes and probed its energy density and power density. The device reached a remarkable power density of 25 kW kg\({}^{-1}\) while maintaining 80% energy density (5.6 W h kg\({}^{-1}\)), which was rationalized assuming that counter-ions can penetrate into nanotubes and thus access internal polymer surfaces. [PERSON] and coworkers also synthesized a flexible pseudocapacitor, this time asymmetric, comprising polymerized PEDOT nanowires as anode and a PEDOT/MnO\({}_{2}\) nanowire array as cathode [150] (Figure 13). The cell exhibited a total capacitance of 0.26 F and a maximum voltage of 1.7 V and is thus capable of powering small portable electronics. Polymer nanowire arrays also find application as chemical sensors, because, like supercapacitors, they also benefit from a large surface area, as this increases the material's interaction with the probed analyte. Nanowires of \(\pi\)-conjugated polymers offer the possibility to sense chemical species (e.g., H\({}^{+}\) and gases) due to their good electrochemical reversibility, good chemical stability and electrical conductivity that can change through interactions with a number of molecules [151; 152; 153]. For example, [PERSON] et al. synthesized hydroquinone monosulfonate-doped polypyrrole (PPy-HQS) nanowires within AAO templates by potentiostatic electropolymerization of a monomer in a solution containing 0.05 M pyrrole + 0.05 M potassium hydroquinone monosulfonate and a basic electrolyte [154]. They tested the efficiency of the nanowire arrays as potentiometric pH sensors and, interestingly, the PPy-HQS nanowires exhibited better performance than on PPy-HQS thin films. A similar nanowire sensor was achieved by [PERSON] et al. by electropolymerizing pyrrole monomers within AAO templates [155]. The device exhibited a high response to the detection of low ammonia concentrations and a comparatively short response and recovery time. [PERSON] et al. also measured the sensing response of PEDOT/PSS nanowires to various vapors, including acetone, methanol and ethanol [156]. The conductivity of the nanowires was 11.5 \(\pm\) 0.7 S/cm, and the contact resistance was 27.6 \(\pm\) 4 k\(\Omega\). In the presence of acetone, methanol and ethanol (at the saturated vapor pressures), the wires showed a resistance change of 10.5%, 9%, and 4%, respectively.