Facet Dependence of CO₂ Reduction Paths on Cu Electrodes

Abstract

Experimental results have shown that CO2 electroreduction is sensitive to the surface morphology of Cu electrodes. We used density functional theory (DFT) to evaluate the thermodynamics and kinetics of CO2 reduction pathways on Cu(100) and Cu(111) with the aim of understanding the experimentally reported differences in CO2 reduction products. Results suggest that the hydrogenation of CO* to hydroxymethylidyne (COH*) or formyl (CHO*) is a key selective step. Cu(111) favors COH* formation, through which methane and ethylene are produced via a common CH2 species under high overpotential (<−0.8 V vs RHE). On Cu(100), formation of CHO* is preferred and ethylene formation goes through C–C coupling of two CHO* species followed by a series of reduction steps of the C2 intermediates, under relatively lower overpotential (−0.4 to −0.6 V vs RHE). Further reduction of these C2 intermediates, however, require larger potentials (∼−1.0 V vs RHE) and conflicts with the experimentally observed low potential pathway to C2 products on Cu(100). Calculations show that the presence of (111) step sites on the flat (100) terrace can reduce the overpotential for C2 production on the Cu electrode, which may be present on Cu(100) due to reconstruction. On Cu(100), a change in CO* coverage from low to high with increasing negative applied potential can trigger a switch from ethylene/ethanol to methane/ethylene as the reduction products by affecting the relative stability of CHO* and COH*.

Full atomistic reaction mechanism with kinetics for CO reduction on Cu(100) from ab initio molecular dynamics free-energy calculations at 298 K

“…Previous calculations of the reaction barrier for CO dimerization have ranged from 0.33 to 1.22 eV, depending on the solvation models and applied potentials (15,(20)(21)(22). Potentials from −0.6 to −0.8 V. The above tendencies for U greater than −0.8 V are reversed for more negative U.…”

“…These various studies led to a range of inconsistent results. For example, the predicted freeenergy barriers for CO dimerization range from 0.33 to 1.22 eV, depending on the solvation model (15,(20)(21)(22). Consequently, we concluded that it is essential to use multiple layers of explicit water to describe reactions at the catalyst-solvent interface properly.…”

“…Quantum-mechanical (QM) calculations can provide atomistic mechanistic insight about CORR (12)(13)(14)(15)(19)(20)(21)(22). However, previous studies have all been deficient in not fully including solvent effects.…”

Electrodeposited Cu-Sn Alloy for Electrochemical CO2 Reduction to CO/HCOO−

“…Cu 100 exhibited high current density despite the large CT resistance, because it showed a high FE for multielectron reduction products, including CH 4 and C 2 H 4 (Fig. 5a) [18,[38][39][40]. Briefly, CO 2 first adsorbs and reduces on Cu surface by accepting an electron and proton, and then forms surface HOCO (*HOCO), which is adsorbed on the electrode.…”

Predicted Structures of the Active Sites Responsible for the Improved Reduction of Carbon Dioxide by Gold Nanoparticles

“…In our previous work 16 and research from other groups, [17][18][19] the reaction mechanism of CO 2 RR to CO on copper (Cu) is as following:…”