Electrochemical Hydrogenation of CO on Cu(100): Insights from Accurate Multiconfigurational Wavefunction Methods

Copper (Cu) remains the most efficacious electrocatalyst
for electrochemical
CO2 reduction (CO2R). Its activity and selectivity
are highly facet-dependent. We recently examined the commonly proposed
rate-limiting CO hydrogenation step on Cu(111) via embedded correlated
wavefunction (ECW) theory and demonstrated that only this higher-level
theory yields predictions consistent with potential-dependent experimental
kinetics. Here, to understand the differing activities of Cu(111)
and Cu(100) in catalyzing CO2R, we explore CO hydrogenation
on Cu(100) using ECW theory. We predict that the preferred pathway
involves the reduction of adsorbed CO (*CO) to *COH via proton-coupled
electron transfer (PCET) at working potentials, although *CHO also
may form with a kinetically accessible but higher barrier. In contrast,
our earlier work on Cu(111) concluded that *COH and *CHO formation
via PCET are equally feasible. This work illustrates one possible
origin of the facet dependence of CO2R mechanisms and products
on Cu electrodes and sheds light on how the selectivity of CO2R electrocatalysts can be controlled by the surface morphology.