Boosting hydrogen peroxide photosynthetic efficiency via enhanced adsorption of small water clusters

Abstract

The bottleneck of overall photosynthesis of hydrogen peroxide (H₂O₂) lies in the slow kinetic water oxidation half-reaction. This inefficiency arises from the principal species of the stable quadrilateral configuration in liquid water, which obstructs the effective extraction of hydrogen from water molecules necessary for the reduction of O₂ to H₂O₂. In this study, the incorporation of sulfonic acid groups into organic polymer photocatalysts induced the adsorption of smaller water clusters with a weak hydrogen bond, leading to enhanced kinetics of the photocatalytic water oxidation reaction. Notably, the introduction of various sulfonic acid groups significantly improved the photocatalytic H₂O₂ production under alkaline conditions (1 M NaOH) without the use of sacrificial reagents. The optimal sulfonated photocatalyst achieved a H₂O₂ production rate of 45.54 µmol h⁻¹, representing a 14-fold increase compared to the pristine one. Furthermore, the solar-to-chemical conversion (SCC) efficiency reached 0.04% in a real outdoor environment, surpassing all previously reported values. Thorough investigations into the underlying mechanisms demonstrated that the incorporation of sulfonate groups enhances the separation efficiency of photogenerated charge carriers. More importantly, this modification led to enhanced adsorption of small water clusters, which mitigated the competition posed by the water oxidation process and ultimately facilitated the extraction of hydrogen from water molecules for the photosynthetic production of H₂O₂.