Long-Term Continuous Conversion of CO₂ to Formic Acid Using Boron-Doped Diamond Electrodes

The long-term durability of boron-doped diamond electrodes (BDD) used continuously in the electrochemical conversion of CO₂ to formic acid was investigated. Although the Faradaic efficiency (FE) for the production of formic acid decreased with increasing electrolysis time, the FE was easily recovered by electrochemical oxidation of the BDD electrodes in H₂SO₄, Na₂SO₄ or K₂SO₄ solutions. For practical application, the long-term production of formic acid using BDD electrodes can be successfully accomplished just by successive polarity reversal of plus and minus terminals. Furthermore, at a current density of -20 mA cm^-2, the rate of production reached 328 μmol h^-1 cm^-2, which is the highest value ever obtained using plate electrodes. Consequently, we found that BDD electrodes are ideal for industrial application of CO₂ reduction.