Semipermanent Continuous Formic Acid Production from CO₂ by Controlling Ion Transport Using Boron-Doped Diamond Electrodes

Boron-doped diamond (BDD) is an excellent functional electrode material used as a working electrode in the electrochemical reduction of CO₂. Formic acid production with approximately 100% Faradaic efficiency has been achieved via CO₂ reduction using BDD electrodes. In this study, we investigated the production performance stability during long-term electrolysis by focusing on ion transport in the electrolyte during electrolysis. Initially, we investigated the behavior of potassium ions (K⁺) and pH during long-term electrolysis in detail. A relationship was observed between the change in ion concentrations and formic acid production, crucial in formic acid production. Based on this knowledge, we successfully achieved stable formic acid production for an extremely long time (1264 h) by controlling ion transport. In addition to utilizing the durability of BDD electrodes as stable electrode materials, controlling ion transport has paved the way for the industrialization of formic acid production via CO₂ reduction.