Increasing greenhouse gas emissions have resulted in greater motivation to find novel carbon dioxide (CO ) reduction technologies, where the reduction of CO to valuable chemical commodities is desirable. Molybdenum-dependent formate dehydrogenase (Mo-FDH) from Escherichia coli is a metalloenzyme that is able to interconvert formate and CO . We describe a low-potential redox polymer, synthesized by a facile method, that contains cobaltocene (grafted to poly(allylamine), Cc-PAA) to simultaneously mediate electrons to Mo-FDH and immobilize Mo-FDH at the surface of a carbon electrode. The resulting bioelectrode reduces CO to formate with a high Faradaic efficiency of 99±5 % at a mild applied potential of -0.66 V vs. SHE.

We demonstrate a novel hydrogel material to facilitate direct bioelectrochemistry of a wide range of redox proteins and enable ATP-independent electroenzymatic reduction of N2 by nitrogenase.

Nitrogenase, the only enzyme known to be able to reduce dinitrogen (N) to ammonia (NH), is irreversibly damaged upon exposure to molecular oxygen (O). Several microbes, however, are able to grow aerobically and diazotrophically (fixing N to grow) while containing functional nitrogenase. The obligate aerobic diazotroph, Azotobacter vinelandii, employs a multitude of protective mechanisms to preserve nitrogenase activity, including a "conformational switch" protein (FeSII, or "Shethna") that reversibly locks nitrogenase into a multicomponent protective complex upon exposure to low concentrations of O. We demonstrate in vitro that nitrogenase can be oxidatively damaged under anoxic conditions and that the aforementioned conformational switch can protect nitrogenase from such damage, confirming that the conformational change in the protecting protein can be achieved solely by regulating the potential of its [2Fe-2S] cluster. We further demonstrate that this protective complex preserves nitrogenase activity upon exposure to air. Finally, this protective FeSII protein was incorporated into an O-tolerant bioelectrosynthetic cell whereby NH was produced using air as a substrate, marking a significant step forward in overcoming the crippling limitation of nitrogenase's sensitivity toward O.