Electrochemical reduction of formic acid through its decarbonylation in phosphoric acid solution

The electrochemical reduction of formic acid on a copper cathode in 85% w/w H3PO4 electrolyte at 70 °C was studied. In this electrolyte formic acid is partially decomposed to carbon monoxide and water. The experimental results showed that the formation of the products is strongly related to the presence of carbon monoxide in the solution and this suggests that CO is the key intermediate for the formation of the detected producs. At −0.45 V vs. Ag/AgCl the main products were CH3OH and CH3CHO with %Current Efficiency (%CE) of 27.6 and 25.8% respectively, whereas a part of the produced methanol(about 50%) was converted to methyl dihydrogen phosphate (25%) and methyl formate (21.8%). At more negative potentials than −0.5 V ethanol was produced by a maximum %CE of 7.9% at −0.75 V. The electrochemical reduction of a CO saturated solution under the same conditions gave the same products albeit the %CE of methanol was lower.