Síntese de Co3O4 submicroestruturado pelo método hidrotermal: caracterização e aplicação como eletrocatalisador da reação de evolução de hidrogênio

Abstract

In this work we report the synthesis Co3O4 by the hydrothermal method in a basic medium without the presence of any additives, such as surfactants or reducing agents. The hydrothermal synthesis was carried out at a temperature of 180 ◦C for a time interval of 3 h. The results revealed the presence of the phases β-Co(OH)2 and Co3O4 in the as synthesized material (precursor). The thermal behavior of the precursor revealed the total thermal decomposition of β-Co(OH)2 into Co3O4 at temperatures above 300 ◦C. The pure-phased Co3O4 with spinel-like cubic structure was obtained after calcination at a temperature of 500 ◦C for a time interval of 3 h. The optical behavior of Co3O4 was characterized by the presence of electronic transitions O2− → Co3+ and O2− → Co2+ centered around 388 and 689 nm, respectively. The results also reveal that the increase in the synthesis time and concentration of Co2+ in the medium promoted the formation of Co3O4 with spherical morphology of diameters around 500 nm. Finally, the Co3O4 microspheres were successfully applied to the hydrogen evolution reaction, showing performance equal to or greater than that of cobalt-based materials reported in the literature. The material was still stable after 5 h of hydrogen evolution at a current density of -10 mA cm−2