Exploring the Impact of Water Content in Solvent Systems on Photochemical CO2 Reduction Catalyzed by Ruthenium Complexes

To achieve artificial photosynthesis, it is crucial to develop a catalytic system for CO₂ reduction using water as the electron source. However, photochemical CO₂ reduction by homogeneous molecular catalysts has predominantly been conducted in organic solvents. This study investigates the impact of water content on catalytic activity in photochemical CO₂ reduction in <i>N,N</i>-dimethylacetamide (DMA), using [Ru(bpy)₃]²⁺ (bpy: 2,2'-bipyridine) as a photosensitizer, 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor, and two ruthenium diimine carbonyl complexes, [Ru(bpy)₂(CO)₂]²⁺ and <i>trans</i>(Cl)-[Ru(Ac-<b>5Bpy</b>-NHMe)(CO)₂Cl₂] (<b>5Bpy</b>: 5'-amino-2,2'-bipyridine-5-carboxylic acid), as catalysts. Increasing water content significantly decreased CO and formic acid production. The similar rates of decrease for both catalysts suggest that water primarily affects the formation efficiency of free one-electron-reduced [Ru(bpy)₃]²⁺, rather than the intrinsic catalytic activity. The reduction in cage-escape efficiency with higher water content underscores the challenges in replacing organic solvents with water in photochemical CO₂ reduction.