Surface Coverage as an Important Parameter for Predicting Selectivity Trends in Electrochemical CO2 Reduction

Andrew R T Morrison; Mahinder Ramdin; Leo J P van der Broeke; Wiebren de Jong; Thijs J H Vlugt; Ruud Kortlever

doi:10.1021/acs.jpcc.2c00520

Surface Coverage as an Important Parameter for Predicting Selectivity Trends in Electrochemical CO₂ Reduction

J Phys Chem C Nanomater Interfaces. 2022 Jul 28;126(29):11927-11936. doi: 10.1021/acs.jpcc.2c00520. Epub 2022 Jul 13.

Authors

Andrew R T Morrison¹, Mahinder Ramdin^{1

2}, Leo J P van der Broeke², Wiebren de Jong¹, Thijs J H Vlugt², Ruud Kortlever¹

Affiliations

¹ Large-Scale Energy Storage, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.
² Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.

Abstract

The electrochemical CO₂ reduction reaction (CO₂RR) is important for a sustainable future. Key insights into the reaction pathways have been obtained by density functional theory (DFT) analysis, but so far, DFT has been unable to give an overall understanding of selectivity trends without important caveats. We show that an unconsidered parameter in DFT models of electrocatalysts-the surface coverage of reacting species-is crucial for understanding the CO₂RR selectivities for different surfaces. Surface coverage is a parameter that must be assumed in most DFT studies of CO₂RR electrocatalysts, but so far, only the coverage of nonreacting adsorbates has been treated. Explicitly treating the surface coverage of reacting adsorbates allows for an investigation that can more closely mimic operating conditions. Furthermore, and of more immediate importance, the use of surface coverage-dependent adsorption energies allows for the extraction of ratios of adsorption energies of CO₂RR intermediates (COOH_ads and HCOO_ads) that are shown to be predictive of selectivity and are not susceptible to systematic errors. This approach allows for categorization of the selectivity of several monometallic catalysts (Pt, Pd, Au, Ag, Zn, Cu, Rh, W, Pb, Sn, In, Cd, and Tl), even problematic ones such as Ag or Zn, and does so by only considering the adsorption energies of known intermediates. The selectivity of the further reduction of COOH_ads can now be explained by a preference for Tafel or Heyrovsky reactions, recontextualizing the nature of selectivity of some catalysts. In summary, this work resolves differences between DFT and experimental studies of the CO₂RR and underlines the importance of surface coverage.