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

Abstract

Abstract We propose a hybrid electrocatalytic‐bioelectrocatalytic reaction cascade integrated on a gas diffusion electrode for CO 2 reduction under selective formation of methanol. Ag‐Bi 2 O 3 selectively reduces gaseous CO 2 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 2 using highly oxygen‐sensitive formate dehydrogenases by more robust inorganic electrocatalysts.