An NADH-Inspired Redox Mediator Strategy to Promote Second-Sphere Electron and Proton Transfer for Cooperative Electrochemical CO₂ Reduction Catalyzed by Iron Porphyrin

Abstract

We present a bioinspired strategy for enhancing electrochemical carbon dioxide reduction catalysis by cooperative use of base-metal molecular catalysts with intermolecular second-sphere redox mediators that facilitate both electron and proton transfer. Functional synthetic mimics of the biological redox cofactor NADH, which are electrochemically stable and are capable of mediating both electron and proton transfer, can enhance the activity of an iron porphyrin catalyst for electrochemical reduction of CO 2 to CO, achieving a 13-fold rate improvement without altering the intrinsic high selectivity of this catalyst platform for CO 2 versus proton reduction. Evaluation of a systematic series of NADH analogs and redox-inactive control additives with varying proton and electron reservoir properties reveals that both electron and proton transfer contribute to the observed catalytic enhancements. This work establishes that second-sphere dual control of electron and proton inventories is a viable design strategy for developing more effective electrocatalysts for CO 2 reduction, providing a starting point for broader applications of this approach to other multi-electron, multi-proton transformations. File list (2) download file view on ChemRxiv CJC_FePorph_NADH_Mimic_CO2RR_ChemRxiv_04202... (2.66 MiB) download file view on ChemRxiv CJC_FePorph_NADH_Mimic_CO2RR_Supporting_Infor... (9.56 MiB)

Optimizing the Electrocatalytic Selectivity of Carbon Dioxide Reduction Reaction by Regulating the Electronic Structure of Single‐Atom M‐N‐C Materials

“…Chang et al. made use of synergistic effect to synthesize NADH functional mimics of biological redox cofactor, [ 170 ] which can accelerate electron and proton transfer to enhance the activity of Fe‐porphyrin catalyst. In addition, the catalytic reduction rate can be significantly increased by 13.4× in the electron‐proton medium without breaking the high selectivity and proton reduction of CO 2 at Fe‐TPP sites.…”

Determining the Overpotential of Electrochemical Fuel Synthesis Mediated by Molecular Catalysts: Recommended Practices, Standard Reduction Potentials, and Challenges

“…A second metal complex can also be used as an overpotential‐reducing proton‐electron mediator [115] . Quinones are common mediators as well, and these have been used in O 2 reduction [116,117] …”

Metal–Ligand Cooperativity via Exchange Coupling Promotes Iron- Catalyzed Electrochemical CO2 Reduction at Low Overpotentials

“…Precedent for the use of redox non-innocent ligands in molecular electrochemical CO 2 RR has shown the viability of this strategy, ,,− along with classic systems bearing strong metal–ligand cooperativity such as metal-dithiolenes for HER. − Indeed, the suppression of metal-centered reductions can limit the formation of off-pathway metal hydride intermediates necessary for hydrogen evolution , and thereby favor CO 2 reduction catalysis. As part of a larger program in electrocatalysis via bioinorganic mimicry, ,,,− our synthetic approach was inspired by mononuclear iron hydrogenase enzymes, which catalyze the reduction of methenyl-H 4 MPT + to methylene-H 4 MPT in methanogenic archaea . In these systems, heterolysis of H 2 and hydride shuttling is enabled by a single redox-innocent iron­(II) site that synergistically interacts with a redox non-innocent guanyl pyridinol cofactor in the primary coordination sphere to provide reducing equivalents (Figure ).…”