(544gi) Electrochemical Charge Transfer Kinetics from Constrained Density Functional Theory

Efficient charge transport properties are often desirable for electrochemical energy conversion and storage materials. First principles density functional theory (DFT) calculations are commonly applied to evaluate electrical conductivity of materials via electron or hole polaron hopping. These techniques, however, implicitly assume these transport mechanisms to be adiabatic, i.e. electronic and nuclear reaction coordinates are directly coupled. Marcus theory¹ can be used to describe charge hopping mechanisms between a charge donor and acceptor, though the Marcus kinetic rate theory depends directly on the off-diagonal Hamiltonian element (electronic coupling, H_ab) between two electronic states. Although Kohn-Sham DFT is based on ground state wave functions, Van Voorhis and co-workers have developed a Constrained Density Functional Theory (CDFT)² approach to calculate the electronic coupling between two diabatic states, recently implemented by Galli and co-workers^3,4 into the Quantum Espresso code. We describe calculations, performed using the Quantum Espresso implementation of CDFT, of diabatic electron transfer kinetics for applications in electrocatalysis and energy storage. In particular, we consider lithium air battery electrochemistry facilitated by transition metal dichalcogenide (TMDC) co-catalysts^5,6 in an imidazolium-based ionic liquid solvent. Based on the calculated electronic couplings, oxygen reduction (during discharge) is likely to proceed adiabatically, wherein O₂ is reduced as it binds to edge sites on the TMDC catalyst. The oxygen evolution reaction upon charge (Li₂O₂ → O₂ + 2 Li) may proceed through diabatic charge transfer, however, due to the large inner reorganization energy associated with superoxide anions in Li₂O₂⁺. We extend these studies to CO₂ reduction to Li₂CO₃ in a Li-CO₂ battery, where adiabatic charge transfer from the TMDC catalyst to reduce CO₂ leads to an increased discharge potential with respect to solution-phase CO₂ reduction potentials.

R.W. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) Program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract number DE-SC0014664.

This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

References

1. R. A. Marcus, Rev. Mod. Phys., 65, 599–610 (1993).
2. B. Kaduk, T. Kowalczyk, and T. Van Voorhis, Chem. Rev., 112, 321–370 (2012).
3. M. Vörös, N. P. Brawand, and G. Galli, Chem. Mater., 29, 2485–2493 (2017).
4. M. B. Goldey, N. P. Brawand, M. Vörös, and G. Galli, J. Chem. Theory Comput., 13, 2581–2590 (2017).
5. M. Asadi et al., ACS Nano, 10, 2167–2175 (2016).
6. M. Asadi et al., Nature, 555, 502–506 (2018).