Hierarchical assembly of donor-acceptor covalent organic frameworks for photosynthesis of hydrogen peroxide from water and air

Covalent organic frameworks (COFs) with ordered pi skeletons and aligned nanopores could be ideal photocatalytic materials but remain unexplored for this use. Here we report hexavalent photocatalytic COFs for efficient photosynthesis via systematic design of the pi skeletons and pores. The framework of the photocatalysts have donor-alt-acceptor arrangements and upon irradiation are converted into catalytic scaffolds, which have dense catalytic sites for oxygen reduction and water oxidation and spatially segregated donor and acceptor columns for hole and electron separation to prevent charge recombination and enable rapid charge transport. The pore walls are engineered to be hydrophilic to enable water and dissolved oxygen to pass through the one-dimensional channel to reach the catalytic sites via capillary effect. The COFs act as a photocatalyst for the photosynthesis of H2O2 using only water, air and light, attaining a high production rate of 7.2 mmol g-1 h-1, optimal apparent quantum yield of 18.0% and solar-to-chemical conversion efficiency of 0.91% in bath reactors. Flow reactors incorporating these COFs can continuously produce pure H2O2 solution, yielding over 15 litres under ambient conditions, and exhibit exceptional operational stability over 2 weeks of use. Exploring artificial photosynthesis with water, air and light is a challenging goal. Here, a donor-acceptor porous framework photocatalyst enables efficient production of hydrogen peroxide from aerated water under ambient conditions.