Artificial photosynthesis with ionic liquids: Interfacial principles, mechanisms and design rules for selective CO₂ conversion

Artificial photosynthesis offers a promising route for the sustainable conversion of CO₂ into fuels and value-added chemicals, yet achieving high selectivity and efficiency remains a major challenge. Ionic liquids (ILs) have emerged as powerful media and interfacial modifiers that can fundamentally alter reaction environments, enabling new pathways for CO₂ activation and reduction. This work examines the role of ILs in artificial photosynthesis, focusing on interfacial principles, mechanistic insights, and design rules governing selective CO₂ conversion. At the molecular level, ILs influence CO₂ adsorption, stabilization of key intermediates, and charge-transfer processes through specific ion–molecule and ion–surface interactions. These effects extend beyond simple solvation, involving the formation of structured interfacial layers that modulate local electric fields, proton availability, and catalytic active sites. Experimental and theoretical studies reveal that IL composition—particularly cation structure and anion basicity—directly impacts reaction pathways, product selectivity, and energy efficiency. Mechanistically, ILs can promote the formation of reactive CO₂•⁻ species, stabilize formate intermediates, or steer multi-electron processes toward C₁ or C₂ products. From these insights, emerging design rules highlight the importance of tuning IL–catalyst interfaces, optimizing ion pairing, and controlling mass transport and light absorption in hybrid systems. Overall, integrating ILs into artificial photosynthetic systems provides a versatile strategy to bridge molecular-level control with macroscopic performance. These findings establish a framework for the rational design of next-generation catalytic systems for selective and efficient CO₂ valorization.