Hydrogen-Bond-Network Breakdown Boosts Selective CO₂ Photoreduction by Suppressing H₂ Evolution

Conventional strategies for highly efficient and selective CO₂ photoreduction focus on the design of catalysts and cocatalysts. In this study, we discover that hydrogen bond network breakdown in reaction system can suppress H₂ evolution, thereby improving CO₂ photoreduction performance. Photosensitive poly(ionic liquid)s are designed as photocatalysts owing to their strong hydrogen bonding with solvents. The hydrogen bond strength is tuned by solvent composition, thereby effectively regulating H₂ evolution (from 0 to 12.6 mmol g^-1 h^-1). No H₂ is detected after hydrogen bond network breakdown with trichloromethane or tetrachloromethane as additives. CO production rate and selectivity increase to 35.4 mmol g^-1 h^-1 and 98.9 % with trichloromethane, compared with 0.6 mmol g^-1 h^-1 and 26.2 %, respectively, without trichloromethane. Raman spectroscopy and theoretical calculations confirm that trichloromethane broke the systemic hydrogen bond network and subsequently suppressed H₂ evolution. This hydrogen bond network breakdown strategy may be extended to other catalytic reactions involving H₂ evolution.