Preparation and optimization of highly active Co3O4 catalyst for hydrogen generation from NaBH4 hydrolysis

The oxidation state and phase structure of oxide catalysts play a crucial role in NaBH4 hydrolysis. In this study, diverse Co3O4 catalysts were synthesized via the EDTA-citric acid complexing method and employed for hydrogen production from NaBH4 hydrolysis. The impacts of different calcination temperatures on crystalline structure, microstructure, and catalytic performance of Co3O4 catalysts were examined systematically. It was observed that the calcination temperature cannot affect the crystal structure of Co3O4 catalysts, but it significantly influences their crystallinity, induction period and catalytic performance. The bulk crystallization of Co3O4 remained unaltered after reduction by NaBH4, while its surface layer would transform into an amorphous phase, forming a core-shell structure. Moreover, the ratio of Co2+/Co3+ on the surface of the Co3O4 catalyst is substantially enhanced and more oxygen defects can be obtained through an in-situ reduction. The experimental results demonstrated that all Co3O4 catalysts exhibit an induction period before attaining a higher hydrogen generation rate. And the intrinsic catalytic activity of Co3O4 catalysts initially increases and then declines with the ascending calcination temperature, whereas their cyclic stability monotonically increases with calcination temperature. The Co3O4 catalyst achieves its highest catalytic activity at 1000 °C and the maximum cyclic stability at 1100 °C.