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

Abstract

The electrochemical CO 2 reduction reaction (CO 2 RR) 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 CO 2 RR selectivities for different surfaces. Surface coverage is a parameter that must be assumed in most DFT studies of CO 2 RR 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 CO 2 RR 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 CO 2 RR and underlines the importance of surface coverage.

Insertion of MXene‐Based Materials into Cu–Pd 3D Aerogels for Electroreduction of CO2to Formate

“…This dramatic change to the catalytic selectivity of Cu-Pd and Cu-Pd/MXene could be related to the difference in the catalysts' surface adsorption properties and their energy barrier toward CO 2 RR intermediates. [80,81] This task was examined with DFT calculation (Figure S36, Supporting Information). In the absence of atomically-resolved Cu-Pd/Mxene surface, the hypothetical structure of MXene with Pd adatom was used to assess the energetics of Cu-Pd/MXene.…”

Electrochemical CO2 Reduction on Copper in Propylene Carbonate: Influence of Water Content and Temperature on the Product Distribution

“…Furthermore, if there is enough adsorbed hydrogen present on the surface, further reduction of CO to CH 4 is possible (pathway in green). [8,42] However, due to the lack of water present in our system, the amount of adsorbed hydrogen on the surface is expected to be limited and this will in turn limit CH 4 formation. Finally, dimerization of the C 1 intermediates can also result in the formation of multicarbon products.…”

The Relevance of the Interfacial Water Reactivity for Electrochemical CO Reduction on Copper Single Crystals

“…As shown in theoretical considerations, the special role of Cu lies in showing ideal CO and H adsorption energies . At present, many different theoretical models assume the importance of either adsorbed H* or H 2 O* for the nature of the products and the selectivity. − Hydrocarbon formation from CO involves the transfer of protons or adsorbed hydrogen from the surface and is, thereby, strongly dependent on the water dissociation.…”