Green Chemistry Approach to Co₃O₄ Synthesis: A Suitable Candidate for Optoelectronics and Energy Storage Devices

Among spinel-type oxides, Co3O4 is noteworthy in energy storage, particularly in solar cells, because of its ability to absorb sunlight across the visible spectrum. This property is associated with its low band gap, making it appropriate for optoelectronic systems. Therefore, it is crucial to provide cost-effective and scalable preparation methods for Co3O4 synthesis. In this study, nano Co3O4 was easily synthesized via a one-pot method, which was a cost-effective and solid-state (solvent-free) approach under “green chemistry” conditions. The structural analyses verified that the most stable phase of cobalt oxide (Co₃O₄) was formed, with nanospheres having particle sizes lower than 50 nm. The nano Co3O4 revealed {111} surface planes, which could be the positive aspect of the synthesized sample due to their performance for oxidation reactions. As well, the synthesized Co3O4 demonstrated a relatively high specific surface area of 53.94 m²/g and a mesoporous structure with pore size distribution ranging from 2 to 50 nm, which can be effective for energy-related systems. The electroactivity of the obtained Co3O4 was confirmed using cyclic voltammetry, revealing a charge transfer resistance equal to 218 (Ω). The charge transfer process involving Co(II) ↔ Co(III) and multiple oxidation states makes Co3O4 a promising candidate for pseudocapacitor, catalyst, and support materials. Optical transitions of the as-synthesized Co3O4 were discovered in two solvents. Band gap energies of Co3O4 obtained by the Tauc plots (1.94 eV) and electrochemical measurement (1.83 eV), confirm its suitability as an efficient material with high electron-hole separation for employment in optoelectrical devices. Additionally, the synthesized Co3O4 shows a ferromagnetic behavior with high thermal stability up to 800 °C.