Exciton Dissociation into Charge Carriers in Porphyrinic Metal-Organic Frameworks for Light-Assisted Li-O 2 Batteries.

Light-assisted Li-O 2 batteries exhibit a high round-trip efficiency attributable to the assistance of light-generated electrons and holes in oxygen reduction and evolution reactions. Nonetheless, the excitonic effect arising from Coulomb interaction between electrons and holes impedes carrier separation, thus hindering efficient utilization of photo-energy. Herein, porphyrinic metal-organic frameworks with (Fe 2 Ni)O(COO) 6 clusters are used as photocathodes to accelerate exciton dissociation into charge carriers for light-assisted Li-O 2 batteries. The coupling of Ni 3d and Fe 3d orbitals boosts ligand-to-metal cluster charge transfer, and hence drives exciton dissociation and activates O 2 for superoxide ( • O 2 - ) radicals, rather than singlet oxygen ( 1 O 2 ) under photoexcitation. These enable the light-assisted Li-O 2 batteries with a low total overvoltage of 0.28 V and round-trip efficiency of 92% under light irradiation of 100 mW cm -2 . This work highlights the excitonic effect in photoelectrochemical processes and provides insights into photocathode design for light-assisted Li-O 2 batteries.