Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces

Abstract

We present a theoretical analysis of trends in overpotentials for electrocatalytic CO2 reduction based on density functional theory calculations. The analysis is based on understanding variations in the free energy of intermediates and mapping out the potential at which different elementary steps are exergonic as a measure of the catalytic activity. We study different surface structures and introduce a simple model for including the effect of adsorbate-adsorbate interactions. We find that high coverages of CO under typical reaction conditions for the more reactive transition metals affect the catalytic activity towards the CO2 reduction reaction, but the ordering of metal activities is not changed. For the hydrogen evolution reaction, a high CO coverage shifts the maximum activity towards more reactive metals than Pt.

Combining theory and experiment in electrocatalysis: Insights into materials design

“…7B consists of DFT calculations that relate the theoretical limiting potential to DFT-calculated ΔE CO (154), and overlaid are experimental onset potentials for the formation of methane and/or methanol, the earliest potentials at which either product is detected (155). In the case of metals that bind CO* too strongly, the overpotential is dictated by the protonation of CO* to CHO*, whereas for metals that bind CO* too weakly, the overpotential is dictated by the protonation of CO (g) to CHO*, where CO desorption is the competing reaction (154). For the formation of methane/methanol, Cu was found to reside near the top of the volcano plot with optimal ΔE CO , albeit with significant theoretical overpotential of ~0.8 V due to limitations from scaling relations (154,155).…”

“…In the case of metals that bind CO* too strongly, the overpotential is dictated by the protonation of CO* to CHO*, whereas for metals that bind CO* too weakly, the overpotential is dictated by the protonation of CO (g) to CHO*, where CO desorption is the competing reaction (154). For the formation of methane/methanol, Cu was found to reside near the top of the volcano plot with optimal ΔE CO , albeit with significant theoretical overpotential of ~0.8 V due to limitations from scaling relations (154,155). This is unsurprising given the many reaction steps and intermediates involved for each product; several of the intermediates are C 1 species that likely bind to the metal in a similar manner, e.g.…”

Promoter Effects of Alkali Metal Cations on the Electrochemical Reduction of Carbon Dioxide

“…This explanation is supported by DFT calculations performed using minimum energy structures of solvated cations at the interface. Since both Cu(100) and Cu(111) surfaces show consistent trends in activity with respect to alkali cation size, the close-packed Cu(111) surface was chosen for the DFT simulations, which has also been frequently used in previous theoretical CO 2 R studies [42][43][44][45] and where the water structure is more well-defined. 46 Because the potentials applied during CO 2 reduction are much more negative than the potential of zero charge (PZC) of the low-index facets of Cu ~ −0.7V SHE 47 , solvated cations should accumulate near the surface of the electrode during reaction.…”

Inhibited proton transfer enhances Au-catalyzed CO 2 -to-fuels selectivity

“…Within this framework, the relative binding energies of adsorbed H and CO, proposed intermediates along HER and CDR pathways, respectively (22)(23)(24)(25)(26)(27)(28)(29)(30), serve as descriptors for the relative rates of each reaction. Computational studies have highlighted that H and CO display differing affinities for surface features, including terraces, edges, and corners (22,23,(29)(30)(31), suggesting a wide distribution of adsorbate binding energies on the polycrystalline metal surfaces that have been the subject of most CDR investigations (18,32).…”

“…Computational studies have highlighted that H and CO display differing affinities for surface features, including terraces, edges, and corners (22,23,(29)(30)(31), suggesting a wide distribution of adsorbate binding energies on the polycrystalline metal surfaces that have been the subject of most CDR investigations (18,32). Additionally, coadsorption of electrolyte ions and CO can play a dominant role in both CO (25,29,30,33,34) and H adsorption (24,26,29). Despite the contemporary emphasis on adsorbate binding energies as key determinants of selectivity in fuel synthesis, the surface adsorbate population has yet to be probed spectroscopically in situ under the conditions of CDR catalysis.…”