Investigação das propriedades estruturais e eletroquímicas de óxidos tipo Perovskita aplicados em armazenamento de energia e eletrólise da água

Abstract

In the midst of growing energy demand and the search for sustainable solutions, the development of new materials for energy storage and conversion has become essential. In this context, supercapacitors and water electrolysis stand out, whose performances are directly related to the electrochemical properties of the materials employed. Knowing that, the objective of this work is to investigate the use of perovskites of PrMO3 and LaMO3 type (M = Co or Ni) as an active material applied as electrode in supercapacitor and as catalysts for the oxygen evolution reaction (OER, which is the anodic half-reaction of water electrolysis). For this purpose, these materials were obtained using the gelatine synthesis method, resulting in four samples (P1, P2, L1 and L2), which were, then, characterized, from a structural point of view, using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV–Vis spectrophotometry and Scanning Electron Microscopy (SEM), and, from a electrochemical point of view, using Cyclic Voltammetry (CV), Galvanostatic Charge–Discharge (GCD), Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), in order to evaluate the specific capacitance and catalytic activity of the materials. Based on the diffraction patterns, the formation of the perovskite phase was confirmed for all samples. FTIR spectra revealed the presence of bands associated with metal–oxygen bonds characteristic of the investigated perovskite families. From the UV–Vis spectra, the band gap energies of the materials were estimated as an indication of their electrical conductivity, which obtained values between 2,20 eV and 3,60 eV. SEM micrographs showed a good distribution of pores and submicrometric particles, forming some agglomerates. Regarding electrochemical performance, the samples exhibited pseudocapacitive behavior, with the highest specific capacitance values obtained for P1 (PrCoO₃ → 184.27 F g⁻¹ at 1 A g⁻¹) and L2 (LaNiO₃/NiO → 142.29 F g⁻¹ at 1 A g⁻¹). Concerning OER activity, the results suggest that the materials present excellent performance, with sample P2 (PrNiO₃/NiO/Pr₆O₁₁) obtaining the lowest overpotential (325 mV with a Tafel slope equal to 56.58 mV.dec⁻¹), the highest electrochemically active surface area (ECSA = 130 cm²), and the lowest charge-transfer resistance. Therefore, the investigated materials are promising candidates for applications as supercapacitor electrodes and OER catalysts.