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 CO reduction under selective formation of methanol. Ag-BiO selectively reduces gaseous CO to formate at neutral pH conditions. A subsequent enzymatic cascade comprising formaldehyde dehydrogenase and alcohol dehydrogenase, which are both nicotinamide adenine dinucleotide (NAD)-dependent, further reduce formate sequentially to formaldehyde and methanol. The enzymatically oxidized 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 reactions and/or to replace bioelectrochemically challenging steps such as the synthesis of formate from CO using highly oxygen-sensitive formate dehydrogenases by more robust inorganic electrocatalysts.