Electrocatalytic Methanol Oxidation in a Gas‐Phase Electrolyzer: Formaldehyde versus Dimethoxymethane Formation

Electrochemical methanol oxidation to formaldehyde (FA) offers several advantages over established thermal production routes, including the potential for the utilization of renewable electricity sources and the formation of H 2 in a separate cathode chamber. Already in 1992, a gas‐phase electrolyzer was presented that selectively oxidized methanol to products like dimethoxymethane (DMM), FA, and methylformate at a Pt‐impregnated Nafion membrane used as anode. The electrolyzer design was claimed to have the additional advantage of achieving FA production with low water content. In this work we adapted the cell design and employed online FTIR gas‐phase analysis. Using the same conditions including 100°C cell temperature and a potential of 1 V versus RHE, a dilemma was identified regarding FA production with low water content. When keeping the cell temperature for many hours at 100°C, the Nafion membrane dehydrated, resulting in a low water amount in the effluent, which led to most of FA reacting with methanol to DMM according to the thermal equilibrium 2 CH 3 OH + CH 2 O ⇌ H 3 C‐O‐CH 2 ‐O‐CH 3 + H 2 O. Thus, all the thermal chemical equilibria releasing water prevent the anodic synthesis of water‐free FA from methanol.