Otimização de espinélios à base de cobalto para reação de evolução de oxigênio em solução alcalina

Abstract

Improving the efficiency of electrocatalysts used as anodes in the oxygen evolution reaction (OER) is crucial for advancing the water electrolysis process, as this step is decisive for the overall rate of electrolysis. Among the materials investigated for this purpose, spinel-type cobaltite stands out due to its multiple oxidation states. In this study, we synthesized spinel-type cobaltite electrodes (MCo2O4, where M = Cu, Mn) on nickel foam using a green synthesis method, employing linseed as a polymerizing agent. The electrodes were directly grown on the porous nickel substrate. The structural, microstructural, and chemical properties of the electrodes were investigated by XRD, SEM, TEM, FTIR, and XPS analyses. The CuCo2O4-CuO composite electrode exhibited a low overpotential of 340 mV vs RHE with a current density of 40 mA cm-2 and a Tafel slope of 71 mV dec-1, demonstrating superior electrocatalytic performance to other Cu and Co-based oxides reported in the literature. The MnCo2O4 electrode showed an overpotential of 319 mV (at a current density of 40 mA cm-2), a Tafel slope of 82 mV dec-1 and excellent electrochemical stability for 15 hours. Therefore, the MnCo2O4 electrode was further optimized with the addition of graphene oxide, achieving the lowest overpotential: 281 mV vs. RHE (40 mA cm-2). Electrochemical impedance spectroscopy (EIS) results during OER demonstrated a decrease in the resistive component associated with surface intermediates with the addition of graphene oxide. This phenomenon suggests an enhanced Faradaic reaction, facilitated by improved electronic conduction. Furthermore, excellent chemical and mechanical stability was demonstrated within the current density range of 10 mA cm-2 to 60 mA cm-2 over 120 hours.