Estudo das variáveis de síntese e o efeito nas propriedades eletroquímicas da polianilina

Abstract

The growing search for clean and renewable energy should be accompanied by the development of efficient energy storage devices. A device of great interest is the electrochemical capacitor, specifically the pseudocapacitors that use a variety of materials such as PANI or metal oxides as electrodes. PANI is an intrinsically conductive polymer that can be synthesized by the chemical or electrochemical route. The first is the most suitable to obtain a PANI with high molecular weight, which is paramount for suggested application. In this regard, this study presents the results of studies of variations in the concentrations of the dopant agent, oxidant agent and chemical synthesis temperature of PANI for possible application in supercapacitors. The materials obtained were characterized by SEM, UV-vis spectroscopy, FTIR, cyclic voltammetry (-0.2 to 1.2 V), galvanostatic loading/discharge, and electrochemical impedance. Structural and optical characterizations proved the polymer obtained in the conductive state for all synthesis conditions. Morphological analyses revealed a decrease in granule size according to increased sulfuric acid concentration (dopant agent). While the second synthesis variable showed smaller granule sizes at the concentration of 2.5 mol. L-1 PSA (oxidizing agent). The temperature variation showed granules on the surface of sticks at the synthesis temperatures of -5 and 0°C, on the other hand, the formation of structures in the form of plates at 5°C occurred. Electrochemical studies by cyclic voltammetry showed different responses for each synthesis condition, having potentials from the redox states of PANI according to the literature and absence of redox peaks in other conditions, mostly, redox processes were observed until the scanning speed of 25 mV.s-1. The capacitance calculated by voltammetry reached the highest values in 224, 271, 328,2 F.g-1, respectively, 0.5 mol. L-1 sulfuric acid, 3,5 mol.L-1 PSA and 0°C, at 10 mV s-1. The highest capacitance values calculated per load/discharge were for the same conditions. And by impedance, all samples showed the presence of semicircle with low load transport resistance and good capacitive effects.