Recent advances in oxygen deficient metal oxides: Opportunities as supercapacitor electrodes

Energy storage devices (ESD) are getting significant attention regarding their ability to reduce fossil fuel usage. Batteries and electrochemical supercapacitors are two well-known ESDs with supercapacitors preferred for their high energy discharge potential. The metal oxides (MOs) with robust redox characteristics are ideal candidates for supercapacitors, although their capacitance still lacks behind the theoretical values. Here, partial reduced or oxygen-deficient MOs have been identified have proven promising to reach the desired capacitance. The introduction of oxygen vacancies into MOs can effectively enhance their electrochemical properties without altering the inherent characteristics of MOs. This review discusses the recent progress on new oxygen-deficient MOs and their performance as a supercapacitor. The importance of oxygen vacancy is described, followed by the traditional synthesis route to producing MOs. The present pathways for generating oxygen vacancies and their analytical assessment are covered in-depth, followed by a section on the most advanced analytical techniques for detecting and interpreting the creation of such vacancies. The influence of oxygen vacancies on the supercapacitive performance of the most researched MOs is provided with the challenges and prospects of oxygen-deficient MOs in supercapacitor application.