Study of Specific Capacitance of Poma/Ptaa Layer-By-Layer Films
Authors: Christinelli Wania , Pereira Ernesto Chaves 
Published: February 2020

Nowadays, capacitors and rechargeable batteries have attracted attention due the urgency efficient and sustainable energy storage devices [1]. Supercapacitors can be classified into two categories depending on the charge storage mechanism: electrochemical double-layer capacitors (EDLCs) and pseudo-capacitors. EDLCs store electrical charge at the interface between surfaces the area electrode and the electrolyte. In the second kind an additional charge can be stored in a reversible electrochemical reactions at the interface. Pseudo-capacitors store a larger amount of charges per gram than an EDLC [2]. A class of smart materials that can be used as pseudo-supercapacitors are the conducting polymers (CPs). The CPs have many advantages, such as high specific capacitance, high conductivity in the charged state and low environmental impact which make them suitable materials for these applications [3]. The charge storage behavior of CPs occurs through reversible redox process that requires the injection of counter ions during the redox cycle. In this sense, the objective of this work is to investigate the Specific Capacitance of layer-by-layer (LBL) films of poly(o-methoxyaniline) (POMA) doping with poly(3-thiophene acetic acid) (PTAA). The LBL films are produced in a multilayered assembled, in which the structure is built via ionic interaction between layers of species with opposite charges. A differential approach of this method is that the self-doping occurs in the different polymeric layers. UV-Visible Spectrophotometer was carried out to evaluate the buildup of LBL films. Cyclic Voltammetry was performed to analyze the Specific Capacitance of the deposited films over ITO substrate, in the potential range varying from −0.2 to 0.2V vs Ag electrode. The potential window was chosen because the POMA is electroactive and PTAA presents no process in this potential region. The assembled of the POMA/PTAA films on ITO substrate presented as a linear growth indicating that the multilayer deposition process is reproducible from layer to layer, i.e., the same amount of polymers is deposited in each bilayer. The results showed that the LBL films presented differences compared with POMA cast films. The Figure 1A displayed a linear increase of the Specific Capacitance as a function of the number of bilayers. This results was not observed for POMA cast films. As presented in the Figure 1B, it was observed that the Specific Capacitance has low variation when the amount of POMA increase. The results show that the properties of conducting polymers can be changed by alternation with layers of appropriate materials in LBL films, suggesting the self-doping effect between POMA and PTAA layers. These results are in agreement with similar polymer systems reported by Trivino-Strixino et al [4,5]. The self-doping effect could arise from the interaction of the anionic carboxylic groups present of the PTAA layers which interact with nitrogen center in POMA chains. In this sense, the PTAA partially compensating the excess charges created during the polymer redox process. The LBL films assembled with POMA/PTAA becomes an interesting material to be used in the development of stored energy devices.
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Acknowledgments: Fapesp

Figure 1