SÍNTESE HIDROTERMAL DE NANOFIOS BINÁRIOS DE Mn E Co: ESTUDO DO EFEITO DA COMPOSIÇÃO NO ARMAZENAMENTO ELETROQUÍMICO DE ENERGIA

Abstract

The climate effects caused by fossil fuels have highlighted the need to search for energy sources that are clean and renewable, such as wind and solar energy. As crucial as this search is the development of devices capable of storing the energy generated by these sources. In this context, supercapacitors (SCs) based on manganese and cobalt oxides stand out as promising materials for energy storage. In this sense, the present study aimed to synthesize manganese oxide nanowires, in its pure form and doped with cobalt in different concentrations of Co (0.4, 1.4, 3.1 and 5.7 wt.%), using the hydrothermal method. Nanowires were studied for their application as active materials in supercapacitors, with the aim of improving the efficiency of these devices. Using Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) techniques, the formation of pure manganese oxide nanowires was observed, exhibiting a well-defined and uniform morphology, with a width of 44 nm and length greater than 1 μm. However, the doped nanowires had defined and uniform dimensions, ranging from 35 to 19 nm. The XRD technique was used to evaluate the structures of the nanomaterials, while the ICP-OES technique confirmed the cobalt concentrations in the MnOx nanowires. The XPS analysis revealed the effect of Co doping on the Mn(IV)/Mn(III) ratio, as this relationship showed a direct correlation with the amount of Co present (a greater amount of Co resulted in a greater proportion of Mn( IV)/Mn(III)), highlighting the crucial role of Co in regulating oxidation states in these materials. It is noteworthy that a sample containing 1.4 wt.% cobalt in the nanowires demonstrated a remarkable specific capacitance of 3204 F g- 1 at a current density of 1 A g-1. The electrode with 1.4 wt.% by weight showed a specific capacitance retention of 92.02% over 5000 charge and discharge cycles. The asymmetric supercapacitor derived from these materials achieved a maximum energy density of 48.08 Wh kg-1 and a maximum power density of 2339.02 W kg-1, indicating its potential as a prominent material for application in high-performance supercapacitors. The characterization results validated the effectiveness of doping, while electrochemical techniques confirmed the application of Co-MnOx (1.4 wt.% Co) in the energy storage process.