The electrochemical reduction of CO₂ has the potential to store energy from intermittent renewable sources and to produce carbon-neutral fuels and chemicals¹. In recent years, theoretical studies of CO₂ reduction have usually applied the computational hydrogen electrode model, which allows for the determination of the energies of reaction intermediates without explicitly treating the potential and the ions in solution². This thermochemical approach has been shown to correlate well with experimental onset potentials ^3,4 and applied to computational screening of new catalysts ^5,6. However, an understanding of charge transfer barriers, kinetics, selectivity, and pH effects all require explicit consideration of solvent and charge. In this talk, I will discuss new developments in the explicit treatment of the electrochemical interface, which is based on a simple capacitor model that uses the interfacial charge to obtain barriers at constant potential ^7,8. I will then discuss the application of such a scheme to CO₂ reduction: the determination of reaction pathways on transition metals, field and solvation effects^9,10, the resultant kinetics, and catalyst design criteria.

1 Whipple, D. T. & Kenis, P. J. A. Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. The Journal of Physical Chemistry Letters 1, 3451-3458, doi:10.1021/jz1012627 (2010).

2 Nørskov, J. K. et al. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B 108, 17886--17892 (2004).

3 Shi, C., Hansen, H. A., Lausche, A. C. & Nørskov, J. K. Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces. Physical Chemistry Chemical Physics 16, 4720-4727, doi:10.1039/C3CP54822H (2014).

4 Kuhl, K. P. et al. Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. Journal of the American Chemical Society, doi:10.1021/ja505791r (2014).

5 Chan, K., Tsai, C., Hansen, H. A. & Nørskov, J. K. Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction. ChemCatChem 6, 1899-1905, doi:10.1002/cctc.201402128 (2014).

6 Asadi, M. et al. Robust carbon dioxide reduction on molybdenum disulphide edges. Nature communications 5 (2014).

7 Chan, K. & Nørskov, J. K. Electrochemical Barriers Made Simple. J. Phys. Chem. Lett., 2663--2668 (2015).

8 Chan, K. & Nørskov, J. K. Potential Dependence of Electrochemical Barriers from ab Initio Calculations. The Journal of Physical Chemistry Letters, 1686-1690, doi:10.1021/acs.jpclett.6b00382 (2016).

9 Montoya, J. H., Shi, C., Chan, K. & Norskov, J. K. Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. The journal of physical chemistry letters 6, 2032--2037 (2015).

10 Chen, L. D., Urushihara, M., Chan, K. & Nørskov, J. Electric Field Effects in Electrochemical CO2 Reduction. ACS Catalysis (2016).

11 Liu, X. et al. Understanding trends in CO2 reductin on transition metals. (2016).