Chemical Synthesis of Polyaniline and Its Composites with Iron, Nickel and Manganese Oxides for Applications in Supercapacitors

Abstract

With the increase in energy consumption added to the risk of depletion of fossil fossils, the need for the development of renewable energy sources for energy storage increases, but these sources are limited due to the variation in availability. Thus, the development of devices that generate and store energy as supercapacitors is widely explored. One of the factors that influence the performance of supercapacitors is the choice of electrode material. They can have double layer capacitance or pseudocapacitive to charge storage systems.Among the materials with EDL capacitive nature, the carbon materials stand out, the carbon fibers (CFs), which have a large specific surface area, high pore accessibility and excellent thermal and chemical stability. In relation to pseudocapacitive materials, examples are conductive polymers (CPs), which combine electrical properties of semiconductors and metals with those of conventional polymers, such as simple preparation and metallic oxides (MOs), which have varying morphologies, high theoretical specific capacitance, in addition to abundant reserves.The materials mentioned above can improve their electrochemical performance when combined due to the synergistic effect. Thus, through the production of hybrid composites, it is possible to produce smaller devices with greater energy efficiency.In this work, the MOs used were Fe2O3, NiO and MnxOy, and the CP used was polyaniline (PANI). Composites of PANI / Fe2O3, PANI / NiO and PANI / MnxOy were obtained. The MOs were obtained via hydrothermal synthesis, and the CP and the composites, via chemical synthesis. These materials were characterized by FEG, FT-IR, XRD, Raman, EIS and CV.Through the analysis of FEG, it was possible to observe agglomerated and granular forms for PANI, which is in accordance with previous studies of chemical polymerization. Through the images of the composites, it is concluded that PANI coated the oxides. It is also observed that there are pores in the morphologies, a desired characteristic for supercapacitor electrode materials.From the FT-MIR spectra of the materials, it was observed that the synthesis was reproductive due to the similarity between them. However, for composites, there was a redshift in the absorption bands, corroborating the structure proposed by NANDAPURE et. al. in which the MO is involved by PANI, so that there is interaction with the imine group. In addition, new bands appeared at the end of the spectrum, related to the presence of metal oxides in the material. Through Raman spectroscopy, it was possible to observe characteristic bands of PANI in the materials spectra. There was an increase in the intensities of the composites bands, due to the interactions of hydrogen bonds between the oxide M-O group and the PANI imine group. The composites showed oxidation degrees closer to 0.5 compared to PANI, indicating a more conductive material.The X-ray diffractograms showed reflections characteristic of the MOs. PANI showed semicritalin nature, with characteristic halos and according to the literature, and they appeared in the diffractograms of the composites, reinforcing the idea of the polymer coating. In addition, the halos become narrower in the composites, favoring crystallinity, especially MnxOy. The materials were subjected to electrochemical analyzes in carbon fiber (CF). The analysis of Electrochemical Impedance Spectroscopy shows capacitive profiles of the synthesized materials with phase angle close to 90 in the regions of medium and low frequencies. In addition, low RTC values and low impedance modulus were observed.By Cyclic Voltammetry, redox peaks characteristic of leukosemeraldina and emerald transition were evidenced related to faradaic processes around 0.2 V and quinone-hydroquinone transitions close to 0.5 V in all materials. For composites, there was an increase in current density, related to the capacitive contribution. Figure 1