Integrated Operation of Artificial-Photosynthetic Reaction and Product Isolation to Output Only Pure Formic Acid

Artificial photosynthetic devices composed of electrochemical reactors powered by solar cells have been significantly improved in recent years to convert CO₂ to useful organic substances, including formic acid. However, the issue of systematic and efficient isolation of the products with low energy consumption has been left unsolved. We tackled this remaining issue in the present study and established an artificial-photosynthetic system in which the reaction process and isolation process are integrated to output only pure formic acid. The synthesized formic acid in the first process dissolved in the specially tuned aqueous electrolyte was first extracted to a mixture of trin-octylamine (TOA) and dichloromethane (DCM) by reactive extraction and then isolated by evaporation of the DCM followed by distillation of the formic acid, achieving an over 90% isolation yield. The great feature of the system is no consumption of chemicals other than the raw materials of CO₂ and water along with no generation of wastes, which is realized by the cyclic use of the electrolyte, TOA, and DCM. This ensures highly sustainable operation of the system.