A review on quaternary oxides for energy conversion and storage

Metal oxides have attracted significant interest due to their tunable optical, electrical, and electrochemical properties, making them essential in energy conversion and storage technologies such as photocatalysis, water splitting, batteries, and supercapacitors. Based on composition, metal oxides are generally classified as binary, ternary, and multicomponent systems. Among them, quaternary metal oxides, containing four distinct elements including oxygen, represent an emerging class of multifunctional materials due to their enhanced compositional flexibility and synergistic electronic interactions. The presence of multiple cations enables effective band structure engineering through orbital hybridization, improved defect chemistry control, and enhanced charge transport compared to binary and ternary oxides. Quaternary oxides, including CuBiVO4 and CoMo2Sb2O10, often exhibit monoclinic (C2/c) space group symmetry due to increased cationic substitution and structural distortion via various methods. This review provides a systematic overview of metal oxide classification and highlights recent progress in quaternary oxide synthesis strategies including solid-state, sol-gel, hydrothermal/solvothermal, combustion, and thin-film techniques. Furthermore, structure-property-performance correlations are discussed to explain how lattice distortion, oxygen vacancies, and morphology influence photocatalytic, photoelectrochemical, and electrochemical energy storage performance. Finally, key challenges such as phase purity control, scalability, and long-term stability are discussed to support future development of quaternary oxides for sustainable energy technologies. This review examines current developments in the synthesis and deposition of quaternary oxides, emphasizing their performance in energy conversion and storage as well as the relationship between structural and synthetic parameters and performance for sustainable technologies.