Engineering product selectivity in photocatalytic CO₂ reduction: fundamentals, mechanisms, and catalyst design

The selective conversion of carbon dioxide (CO₂) into value-added products using solar energy represents a promising strategy for addressing climate change and advancing carbon-neutral energy systems. However, the inherent complexity of photocatalytic CO₂ reduction, involving multielectron and multiproton transfer steps with competing pathways, often leads to poor selectivity. This review provides a comprehensive overview of recent five-year advances and mechanistic insights into product selectivity in photocatalytic CO₂ reduction. The thermodynamic and kinetic fundamentals governing CO₂ activation were outlined, and the key intermediates and charge-carrier dynamics that dictate product distribution were then highlighted. Strategies for enhancing selectivity, including crystal facet engineering, cocatalyst integration, multi-active site design, and modulation of catalyst microenvironments, are subsequently discussed with representative examples. Advanced characterization techniques are examined for their role in elucidating structure-selectivity relationships. Finally, emerging trends are addressed, including artificial intelligence-driven catalyst discovery, tandem reactor systems, selective C₂₊ fuel production, and sustainable materials and device engineering. This review aims to provide design principles and forward-looking perspectives to guide the development of efficient, durable, and highly selective photocatalytic CO₂ conversion systems.