Recent advances in defect engineering vacancies of indium oxide nanomaterials for CO₂ photoreduction

Oxygen vacancies have transformed In₂O₃ from a conventional semiconductor into one of the most promising photocatalysts for solar-driven CO₂ reduction. Rather than acting as isolated defects, they define the electronic structure, catalytic active sites, and reaction pathways that govern photocatalytic performance. This review highlights the emerging transition from increasing vacancy concentration to engineering vacancy architecture through precise control of defect location, distribution, clustering, and stability. We critically discuss recent advances in defect engineering, characterization techniques, and theoretical understanding while identifying current limitations in defect quantification and catalyst evaluation. Finally, key challenges, including operando characterization, quantitative defect descriptors, long-term stability, selective C₂₊ production, and scalable catalyst design, are presented. By integrating these perspectives, this review provides a framework for the rational engineering of vacancy-controlled In₂O₃ photocatalysts for efficient and durable CO₂ conversion.