Creating a Low‐Potential Redox Polymer for Efficient Electroenzymatic CO₂ Reduction

Abstract

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.

Recent Enzymatic Electrochemistry for Reductive Reactions

“…The coupling of this Cc‐PAA redox polymer with Mo‐dependent Fdh from E. coli demonstrated that a high FE of 99 % could be achieved at a mild applied potential of −0.66 V vs . SHE for CO 2 reduction to HCOO − …”

Enhanced Electrosynthetic Hydrogen Evolution by Hydrogenases Embedded in a Redox‐Active Hydrogel

“…One such redox polymer is cobaltocene‐functionalized polyallylamine (Cc‐PAA), recently reported by Yuan et al . This polymer functions in an electroenzymatic system to immobilize the enzyme in a polymer mesh in close proximity to the electrode, and to efficiently mediate electron transfer from the electrode surface to the enzyme via cobaltocene functional groups.…”

“…Cc‐PAA has been shown to mediate electron transfer from an electrode to formate dehydrogenase and diaphorase, however other enzyme classes remain to be tested . Concurrently, the NiFe hydrogenase HynAB from Desulfovibrio gigas has been shown to accept electrons from cobaltocene‐functionalized branched polyethylenimine (Cc‐BPEI) in a photoelectrochemical setup .…”

“…PAA is similar in structure to BPEI, but forms a more rigid polymer and has higher stability . Furthermore, Cc‐PAA has a more negative redox potential (−0.576 V vs. SHE) than Cc‐BPEI (−0.550 V vs. SHE), which provides a stronger driving force for reduction of protons to hydrogen at the hydrogenase …”

“…Inset: Chemical structure of the polyallylamine backbone functionalized with cobaltocene functional groups. Adapted from Yuan et al …”