Understanding trends in electrochemical carbon dioxide reduction rates

Abstract

Electrochemical carbon dioxide reduction to fuels presents one of the great challenges in chemistry. Herein we present an understanding of trends in electrocatalytic activity for carbon dioxide reduction over different metal catalysts that rationalize a number of experimental observations including the selectivity with respect to the competing hydrogen evolution reaction. We also identify two design criteria for more active catalysts. The understanding is based on density functional theory calculations of activation energies for electrochemical carbon monoxide reduction as a basis for an electrochemical kinetic model of the process. We develop scaling relations relating transition state energies to the carbon monoxide adsorption energy and determine the optimal value of this descriptor to be very close to that of copper.

Machine-Learning Methods Enable Exhaustive Searches for Active Bimetallic Facets and Reveal Active Site Motifs for CO2 Reduction

“…In the microkinetic model, all free energies and kinetic barriers are assumed to be linearly dependent on either the CO adsorption energy or the transition state energy of the CO to CHO protonation step. 5 This allows the activity of a material to be predicted solely based on these two values, as illustrated in Figure 6. Typical scaling relations for the transition state energy vs the CO adsorption energy are also shown for terrace and step active sites.…”

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.…”

“…43,49,52 The change in adsorption free energy for each species was determined by applying a uniform field oriented perpendicular to the surface in vacuum. 43 The corresponding values of µ and α, determined by fitting Eq. (1) the calculated data, are given in Table 1.…”

“…53 Recent calculations of the electrochemical barriers for CO 2 reduction using an explicit solvent model have shown that reduction of *CO to form *CHO is the limiting step for CH 4 formation. 43 Since the value of µ for *CHO is zero, the cation-induced field would stabilize *CO and therefore increase the energy barrier for hydrogenation to *HCO, the rate-limiting step on the path to CH 4 formation. Therefore, CH 4 formation should occur in regions of the catalyst that are not strongly influenced by the cations located at the outer Helmholtz plane, and correspondingly the partial current density for CH 4 should not be strongly affected by cation identity, which is consistent with the trend in the experimental data shown above.…”

Electrocatalytic Metal–Organic Frameworks for Energy Applications

“…[17,19,121] Additionally, proton reduction is ac ompetitive and kinetically competent pathway in water,t he preferred solvents ystem,s ot he design of catalysts that are selectivef or the CO 2 reduction reactioni s paramount. [20,120,123] …”