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The development of electrodes for efficient CO 2 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 ( Ch CODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO 2 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 CO 2 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 CO 2 into CO without any parasitic co-reactions at the applied potentials.

We report on the fabrication of bioanodes for H 2 oxidation based on [NiFeSe] hydrogenase. The enzyme was electrically wired by means of a specifically designed low-potential viologen-modified polymer, which delivers benchmark H 2 oxidizing currents even under deactivating conditions owing to efficient protection against O 2 combined with a viologen-induced reactivation of the O 2 inhibited enzyme. Moreover, the viologen-modified polymer allows for electrochemical co-deposition of polymer and biocatalyst and, by this, for control of the film thickness. Protection and reactivation of the enzyme was demonstrated in thick and thin reaction layers., Competing Interests: The authors declare no competing financial interest., (Copyright © 2017 American Chemical Society.)