Defect Engineering in Transition Metal Oxides for Energy, Environmental, and Materials Technology Applications: A Comprehensive Review

Transition metal oxides (TMOs) have emerged as one of the most promising classes of functional materials due to their outstanding electrical, optical, catalytic, and chemical properties. Their versatile characteristics make them highly suitable for applications in energy storage, photocatalysis, gas sensing, environmental remediation, and electronic devices. In recent years, defect engineering has become an effective strategy for enhancing the performance of transition metal oxides by tailoring their structural and electronic properties. Defects such as oxygen vacancies, interstitial atoms, surface defects, and dopant-induced imperfections significantly influence charge transport, light absorption, catalytic activity, and ion diffusion behavior. This review provides a comprehensive overview of defect engineering approaches in transition metal oxides and their impact on energy and environmental applications. The review discusses the fundamental concepts of crystal defects, synthesis techniques, and advanced characterization methods used to investigate defect structures in metal oxides. Various defect engineering strategies, including oxygen vacancy generation, elemental doping, surface modification, heterostructure formation, and strain engineering, are critically analyzed. Furthermore, the review highlights recent developments in photocatalysis, lithium-ion batteries, supercapacitors, gas sensors, and optoelectronic devices based on defect-engineered metal oxides. The major challenges related to structural stability, scalability, and environmental sustainability are also discussed.