Advances and roles of oxygen vacancies in semiconductor photocatalysts for solar-driven CO₂ reduction

Rising CO₂ emissions from fossil fuel combustion and human activities pose a serious challenge to energy sustainability and environmental health, and the reduction of CO₂ into high added-value carbon fuels and chemicals through photocatalytic reduction is considered to be an effective strategy to simultaneously address global environmental issues and the energy crisis. Photocatalytic CO₂ reduction into renewable energy sources, particularly through the use of semiconductor photocatalysts like titanium dioxide (TiO₂), presents a promising avenue to alleviate greenhouse gas impacts while addressing the energy crisis. However, the efficiency and selectivity of CO₂ photoreduction are hampered by the inherent limitations of photocatalysts, including poor light utilization and ineffective charge carrier dynamics. This review article focuses on the transformative role of oxygen vacancies (OVs) in enhancing the photocatalytic performance for CO₂ reduction. It highlights the pivotal advances in oxygen vacancy engineering within semiconductor photocatalysts, notably TiO₂ and Bi-based materials, for improved solar-driven CO₂ reduction. By facilitating CO₂ adsorption and activation, extending light absorption, and promoting charge carrier separation, OVs emerge as critical modifiers to augment photocatalytic efficiency and selectivity towards valuable carbon-based fuels. This comprehensive review not only scrutinizes the mechanisms by which OVs enhance photocatalytic activity but also delves into the challenges of OV concentration control, photocatalyst stability, and synthesis scalability. Moreover, it emphasizes the urgent need for advancing semiconductor photocatalyst selectivity to elevate the utility of CO₂ photoreduction technology. The practical applications for environmental remediation underline the real-world significance of advancing OV-engineered photocatalysts. By integrating recent findings with methodological insights, the article offers new directions for future research aimed at the development of efficient and selective photocatalysts for sustainable CO₂ reduction.