Confining asymmetric water hydrogen-bond network to boost photoreduction of CO2 to formaldehyde

Overall photocatalytic CO₂ reduction with H₂O to value-added HCHO is a promising route to achieve the carbon neutrality goal. However, the efficiency of the CO₂ reduction half-reaction is constrained by the structural configuration of the hydrogen bond network of water on the catalyst surface, because it controls the H₂O dissociation half-reaction that was deemed as the rate-determining step in the overall CO₂ reduction reaction. Herein, we propose a novel concept of confining an asymmetric water hydrogen-bond network to enhance H₂O dissociation, thereby providing protons for CO₂ reduction and significantly increasing the rate of HCHO formation. As a demonstration of feasibility, sulfur-doped graphite carbon nitride (g-C₃N₄-S) was successfully prepared as the desired prototype photocatalyst. We unravel that −SO_x species on g-C₃N₄-S photocatalyst enhance the adsorption concentration of CO₂ and *CO intermediate by promoting the adsorption of H₂O. More importantly, −SO_x species boosts the dissociative adsorption of H₂O due to altering the symmetric water hydrogen bonding network on the interface into a confining asymmetric one, thereby accelerating the activation and conversion of CO₂ adsorbed on the catalyst surface. As a result, the production of HCHO over the g-C₃N₄-S (180.9 μmol) has increased 2.5 times compared to the pristine g-C₃N₄ (72.9 μmol). The novel approach of enhancing CO₂ photoreduction efficiency by regulating the water hydrogen-bond network structure at the interface offers a promising avenue for advancing CO₂ conversion efficiency.