Low-temperature synthesis of porous Co₃O₄ thin films through two approaches: metal organic framework-decomposition and solution combustion methods

Abstract

Porous Co₃O₄ thin films were prepared at low temperatures by two different methods: solution combustion (SC), and decomposition of Co-containing metal organic framework (MOF) thin films. The former method involved spin coating of 2-methoxyethanol solution containing Co²⁺ ions, acetylacetone, and ammonia, followed by calcination in the temperature range from 473 to 773 K. The latter method involved the spontaneous deposition of Co(MeIM)₂ (MeIM = 2-methylimidazol) MOF flat thin films on substrates, followed by decomposition at temperatures higher that 573 K to obtain porous Co₃O₄ thin films. The SC method produced electrochemically active and reversible thin films at a low final processing temperature of 473 K, allowing the deposition of porous Co₃O₄ layers onto polymer substrates. The MOF-decomposition yielded thin films with similar electrochemical activity and reversibility as those of the films obtained by the SC method at a processing temperature of 573 K. In both methods, an increase in the final processing temperature promoted the sintering of the porous structured thin films, leading to the formation of dense structures, which caused a deterioration in the electrochemical activity.