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

We show a great possibility of mediated enzymatic bioelectrocatalysis in the formate oxidation and the carbon dioxide (CO2) reduction at high current densities and lowoverpotentials. 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 (j(lim)) of ca. 24 mA cm(-2) was realized with a half wave potential (E-1/2) of only 0.12 V more positive than the formal potential of the formate/CO2 couple (E degrees' CO2) at 30 C in the presence of methyl viologen (MV2+) as a mediator, and j(lim) reached ca. 145 mA cm(-2) at 60 degrees C. Even when a viologen-functionalized polymer was co-immobilized with FoDH1 on the porous electrode, j(lim) of ca. 30 mA cm(-2) was attained at 60 degrees C with E-1/2 = E degrees' CO2 + 0.13 V. On the other hand, the CO2 reduction was also realized with j(lim) approximate to 15 mA cm(-2) and E-1/2 = E degrees' CO2 - 0.04 V at pH 6.6 and 60 degrees C in the presence of MV2+. (C) 2016 Elsevier B.V. All rights reserved.