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.