Bioelectrocatalytic formate oxidation and carbon dioxide reduction at high current density and low overpotential with tungsten-containing formate dehydrogenase and mediators

Abstract

We show a great possibility of mediated enzymatic bioelectrocatalysis in the formate oxidation and the carbon dioxide (CO2) reduction at high current densities and low overpotentials. Tungsten-containing formate dehydrogenase (FoDH1) from Methylobacterium extorquens AM1 was used as a catalyst and immobilized on a Ketjen Black-modified electrode. For the formate oxidation, a high limiting current density (jlim) of ca. 24mAcm−2 was realized with a half wave potential (E1/2) of only 0.12V more positive than the formal potential of the formate/CO2 couple (E°′CO2) at 30°C in the presence of methyl viologen (MV2+) as a mediator, and jlim reached ca. 145mAcm−2 at 60°C. Even when a viologen-functionalized polymer was co-immobilized with FoDH1 on the porous electrode, jlim of ca. 30mAcm−2 was attained at 60°C with E1/2=E°′CO2+0.13V. On the other hand, the CO2 reduction was also realized with jlim≈15mAcm−2 and E1/2=E°′CO2−0.04V at pH 6.6 and 60°C in the presence of MV2+.