THE ELECTROCHEMICAL CONVERSION OF CARBON-DIOXIDE INTO METHANOL - THE FORMIC-ACID REDUCTION STEP IN ACIDIC SOLUTIONS

Various studies have shown that the electrode reduction of CO//2 in water using metal electrodes yields formic acid as the main product. Recent publications have generated conflicting claims regarding the further reduction of formic acid to methanol using TiO//2 electrodes. Our cyclic voltammetric studies using TiO//2, Ti, In, Ag, Pt and other electrodes at a fixed pH in mildly acidic NaClO//4 solutions show an increase in the cathodic current when NaCOOH is added. The current increases linearly with the concentration of the NaCOOH added if the pH is kept constant; this suggests that formic acid participates in the reduction reaction. Closer examinations, however, that include constant potential coulometry studies show that the HCOOH/HCOO** minus equilibrium is involved and that H//3O** plus rather than HCOOH is reduced. Undissociated HCOOH molecules aid the cathodic reaction by serving as a conveyor of protons to the electrode surface.