SÍNTESE E APLICAÇÃO DE MATERIAIS CATALÍTICOS PARA REAÇÕES DE CONVERSÃO ELETROQUÍMICA DE ENERGIA

Abstract

This work investigated the development and application of catalytic materials as alternatives to platinum for electrochemical energy conversion systems. In the first chapter, silver phosphate (Ag₃PO₄) and its derived phase, silver(I) oxide (Ag₂O), were evaluated as catalysts for the oxygen reduction reaction (ORR) in alkaline média. X-ray diffraction analyses confirmed the partial transformation of Ag₃PO₄ into Ag₂O after contact with the electrolyte, indicating the in situ formation of the catalytically active phase. Electrochemical measurements revealed onset and half-wave potentials close to those of the commercial Pt/C (20%) catalyst, highlighting the promising electrocatalytic performance of Ag₂O. Mechanistic analysis, combining experimental results and theoretical calculations based on slab geometry relaxation, indicated that the ORR proceeds predominantly via a four-electron pathway, initially following a peroxide-mediated route, along with favorable kinetics in alkaline conditions. In the second chapter, a Co₃O₄|HCNS|Pt nanocomposite was investigated for the hydrogen evolution reaction (HER) and the methanol oxidation reaction (MOR). Optical analyses indicated a narrowing of the band gap compared to the FTO substrate, suggesting photoelectrochemical potential. Electrochemical responses showed a strong dependence on the operating regime, with a photoassisted effect evidenced by chronoamperometry under constant potential. The composite also exhibited electrocatalytic activity toward methanol oxidation, with improved performance at intermediate potentials. Overall, the results indicate that Ag₂O exhibits good electrocatalytic performance for the oxygen reduction reaction in alkaline media, while the Co₃O₄|HCNS|Pt composite shows promise for electrochemical and photoelectrochemical energy conversion applications. However, for the latter, structural and interfacial limitations still require optimization of the synthesis route and material architecture.