Hybrid Enzyme‐Electrocatalyst Cascade Modified Gas‐diffusion Electrodes for Methanol Formation from Carbon Dioxide

We propose a hybrid electrocatalytic-bioelectrocatalytic reaction cascade integrated on a gas diffusion electrode for CO2 reduction under selective formation of methanol. Ag-Bi2O3 selectively reduces gaseous CO2 to formate at neutral pH conditions. A subsequent enzymatic cascade comprising formaldehyde dehydro-genase and alcohol dehydrogenase, which are both nicotinamide adenine dinucleotide (NAD)-dependent, further reduce formate sequentially to formaldehyde and methanol. The enzymatically oxi-dized redox cofactor NAD+ is regenerated through the enzyme diaphorase which is electrochemically coupled to the electrode by embedding it into a cobaltocene-based low-potential redox polymer. Methanol formation is confirmed using a highly selective biosensor based on alcohol oxidase in combination with horseradish peroxidase integrated into a specifically adapted redox polymer. The proposed hybrid electrocatalytic-bioelectrocatalytic cascade is an example for a general strategy for enhancing the selectivity of electrocatalytic reac-tions and/or to replace bioelectrochemically challenging steps such as the synthesis of formate from CO2 using the highly oxygen-sensitive formate dehydrogenase by more robust inorganic electrocatalysts.