Nb₂O₅-based photocatalysts for CO₂ reduction: Advances and prospects

Photocatalytic CO₂ reduction represents a promising strategy for solar-to-fuel conversion, yet its mechanistic validity and visible-light performance remain widely debated. Niobium pentoxide (Nb₂O₅) has emerged as a distinctive oxide platform for CO₂ reduction owing to its delocalized 4d-derived conduction band, tunable Nb4+–Vo defect states, and band-edge positions compatible with multi-electron CO₂ reduction and oxidative half-reactions. Unlike previous reviews that primarily focus on material modifications, this work provides a comprehensive outline of Nb₂O₅-based photocatalytic systems adopted for CO₂ reduction. The review was introduced by a concise discussion of Nb₂O₅ core merits as a potent catalyst for CO₂ reduction. Then, the CO₂ reduction process was discussed from thermodynamic, kinetic, and mechanistic perspectives. Afterwards, we critically analyzed how morphology and bandgap engineering, controlled defect engineering, heterojunction formation, and cocatalyst integration can modulate charge-carrier dynamics, CO₂ adsorption, intermediate stabilization, and product selectivity. In addition, a theoretical insight based on density functional theory (DFT) calculations was conveyed to unravel the structure-activity interplay and reaction mechanism of CO₂ conversion over Nb₂O₅-based photocatalytic systems. Finally, current limitations and outlooks are provided to motivate future studies on developing Nb₂O₅-based photocatalysts with adequate reactivity, selectivity, and stability.