Enhanced Hydrogen Peroxide Photosynthesis Using X-Packed Cocrystal Catalysts

Hydrogen peroxide (H₂O₂) is an essential chemical and potent energy carrier. Its production through solar energy and metal-free photocatalysts is desirable. Organic semiconductors, as a new generation of semiconductors, can form suitable transition state intermediates showing great ability in enhancing the efficiency and selectivity of photocatalytic H₂O₂ generation, offering a metal-free, green, and more economical solution. However, the smaller Frenkel exciton radius and larger exciton Coulomb binding energy lead to a constrained capacity for exciton dissociation, blocking the way of photocatalysts based on organic semiconductors. Here, we overcome the bottleneck by cocrystal engineering. A kind of cocrystal photocatalysts with X-packing are designed and synthesized, which permit all excited states to be optically allowed due to reduced energy splitting, enhancing the exciton participation in photosynthesis of H₂O₂ giving much more efficient singlet exciton dissociation and exciton utilization. Indeed, the X-packed cocrystals show photosynthesis of H₂O₂ from O₂ and H₂O at a rate of 2.65 mmol h^-1 g^-1 and a solar-chemical energy conversion efficiency of 0.42%, which can be further improved to 13.3 mmol h^-1 g^-1 with a hole sacrificial agent. This work seems to open a new door for high solar exciton utilization with organic semiconductors by cocrystal engineering.