Bioelectrocatalytic CO₂ Reduction by Redox Polymer-Wired Carbon Monoxide Dehydrogenase Gas Diffusion Electrodes

The development of electrodes for efficient CO₂ reduction while forming valuable compounds is critical. The use of enzymes as catalysts provides the advantage of high catalytic activity in combination with highly selective transformations. We describe the electrical wiring of a carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans (ChCODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO₂ to CO over gas diffusion electrodes. High catalytic current densities of up to -5.5 mA cm^-2 are achieved, exceeding the performance of previously reported bioelectrodes for CO₂ reduction based on either carbon monoxide dehydrogenases or formate dehydrogenases. The proposed bioelectrode reveals considerable stability with a half-life of more than 20 h of continuous operation. Product quantification using gas chromatography confirmed the selective transformation of CO₂ into CO without any parasitic co-reactions at the applied potentials.