Proton‐Enriched Alginate–Graphene Hydrogel Microreactor for Enhanced Hydrogen Peroxide Photosynthesis

Abstract

Abstract Efficient synthesis of H 2 O 2 via photocatalytic oxygen reduction without sacrificial agents is challenging due to inadequate proton supply from water and difficulty in maintaining O−O bond during O 2 activation. Herein, we developed a straightforward strategy involving a proton‐rich hydrogel cross‐linked by metal ions [M(n)], which is designed to facilitate the selective production of H 2 O 2 through proton relay and metal ion‐assisted detachment of crucial intermediates. The hydrogel comprises CdS/graphene and alginate cross‐linked by metal ions via O=C−O−M(n) bonds. Efficient O 2 reduction and hydrogenation occurred, benefitting from the collaboration between proton‐rich alginate and the photocatalytically active CdS/graphene. Meanwhile, the O=C−O−M(n) bonds enhance the electron density of α‐carbon sites on graphene, crucial for O 2 activation and *OOH intermediate detachment, preventing deeper O−O bond cleavage. The role of metal ions in promoting *OOH desorption was demonstrated through Lewis acidity‐dependent activity, with Y(III) having the highest activity, followed by Lu(III), La(III), and Ca(II).