The electrochemical reduction of CO₂ and CO has been extensively studied in the past few years, as it can convert such harmful oxides into useful compounds such as CH₄, C₂H₄ and CH₃CH₂OH, using copper-based catalysts (1, 2). However, large overpotentials and low selectivities currently make CO₂ electrolyzers commercially inviable, in spite of the low price and relatively high abundance of copper.

Therefore, it is vital to determine the structure-activity relationships that control the product selectivity as well as the reasons for the high overpotentials, so that enhanced catalysts can be rationally designed. In this talk, I will show a reaction mechanism obtained with DFT calculations for CO electroreduction to C₂H₄, CH₃CHO, and CH₃CH₂OH on Cu(100) electrodes (3, 4). The mechanism proceeds via a (hydrogenated) CO dimer intermediate which can be observed experimentally (5). Based on the structure-activity relationships for Cu catalysts, I will explain the conspicuous preference of (100) terraces towards the production of C₂ species such as C₂H₄ and CH₃CH₂OH. Importantly, such preference stems from the breaking of adsorption-energy scaling relations on Cu(100) (6).

Furthermore, the proposed mechanism predicts that the late stages of the electroreduction of CO to CH₃CH₂OH correspond to CH₃CHO reduction (3, 4). Evaluating experimentally and theoretically the structure-activity relationships of CH₃CHO reduction on various single-crystal Cu electrodes suggests that the selectivity of Cu catalysts towards CH₃CH₂OH or C₂H₄ can be tweaked by introducing certain undercoordinated sites (7).

References

1. M. Gattrell, N. Gupta and A. Co, Journal of Electroanalytical Chemistry, 594, 1 (2006).

2. R. Kortlever, J. Shen, K. J. P. Schouten, F. Calle-Vallejo and M. T. M. Koper, The Journal of Physical Chemistry Letters, 6, 4073 (2015).

3. F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie International Edition, 52, 7282 (2013).

4. K. J. P. Schouten, F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie International Edition, 53, 10858 (2014).

5. E. Pérez-Gallent, M. C. Figueiredo, F. Calle-Vallejo and M. T. M. Koper, Angewandte Chemie, 129, 3675 (2017).

6. H. Li, Y. Li, M. T. M. Koper and F. Calle-Vallejo, Journal of the American Chemical Society, 136, 15694 (2014).

7. I. Ledezma-Yanez, E. P. Gallent, M. T. M. Koper and F. Calle-Vallejo, Catalysis Today, 262, 90 (2016).