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Reducing CO2 to HCO2- at Mild Potentials: Lessons from Formate Dehydrogenase

preprint
submitted on 16.07.2020 and posted on 16.07.2020 by Jenny Yang, Tyler Kerr, Xinran S. Wang, Jeffrey Barlow
The catalytic reduction of CO2 to HCO2- requires a formal transfer of a hydride (two electrons, one proton). Synthetic approaches for inorganic molecular catalysts have exclusively relied on classic metal hydrides, where the proton and electrons originate from the metal (via heterolytic cleavage of an M-H bond). An analysis of the scaling relationships that exist in classic metal hydrides reveal that hydride donors sufficiently hydridic to perform CO2 reduction are only accessible at very reducing electrochemical potentials, which is consistent with known synthetic electrocatalysts. By comparison, the formate dehydrogenase enzymes operate at relatively mild potentials. In contrast to reported synthetic catalysts, none of the major mechanistic proposals for hydride transfer in formate dehydrogenase proceed through a classic metal hydride. Instead, they invoke formal hydride transfer from an orthogonal or bi-directional mechanism, where the proton and electron are not co-located. We discuss the thermodynamic advantages of this approach for favoring CO2 reduction at mild potentials, along with guidelines for replicating this strategy in synthetic systems.

Funding

DE-0000243266

History

Email Address of Submitting Author

j.yang@uci.edu

Institution

University of California, Irvine

Country

United States

ORCID For Submitting Author

0000-0002-9680-8260

Declaration of Conflict of Interest

No conflict of interest

Version Notes

July 15, 2020 Version 1

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