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Abstract
Density functional theory calculations employing a hybrid implicit/explicit solvation method were used to explore
a new strategy for electrochemical conversion of CO2 using an electro-organocatalyst. A particular structural motif
is identified that consists of an electron-rich >N−C=C−N< (enediamine) backbone which is capable of activating
CO2 by formation of a C−C bond while subsequently facilitating the transfer of electrons from a chemically inert
cathode to ultimately produce formaldehyde. Unlike transition metal-based electrocatalysts, the electroorganocatalyst is not constrained by scaling relations between the formation energies of activated CO2 and
adsorbed CO, nor is it expected to be active for the competing hydrogen evolution reaction. The rate limiting steps
are found to occur during two proton-coupled electron transfer (PCET) sequences and are associated with the
transfer of a proton from a proton transfer mediator to a carbon atom on the electro-organocatalyst. The difficulty
of this step in the second PCET sequence necessitates an electrode potential of −0.94 V vs. RHE to achieve the
maximum turnover frequency. In addition, it is postulated that the electro-organocatalyst should also be capable
of forming long chain aldehydes by successively carrying out reductive aldol condensation to grow the alkyl chain
one carbon at a time. While much effort is still required to bring this conceptual design to reality, we are optimistic
that the new directions for CO2 conversion opened up by this initial work will one day result in a practical device
for electrochemical conversion of CO2 into multicarbon products.
Supplementary materials
Title
Computational Design of an Electro-Organocatalyst for Conversion of CO2 into Formaldehyde
Description
Density functional theory calculations were performed using the Vienna Ab-initio Simulation Package
(VASP) combined with the VASPsol extension for including an implicit electrolyte in the simulation.
The exchange-correlation energy was computed at the generalized gradient approximation level using the
Bayesian error estimation functional with van der Waals correlation (BEEF-vdW) 4. The wave functions
were constructed using plane waves with an energy up to 400 eV, while the projector augmented wave
(PAW) method was used to represent the oscillations in the core region. The Kohn-Sham orbital
populations were determined using an error function distribution having a width of 0.2 eV and the energy
was extrapolated to zero temperature. All species were placed in a 20×20×20 Å unit cell and only the Γ-
point was used to sample the Brillouin zone.
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