Quantum Mechanical Screening of Single-Atom Bimetallic Alloys for the Selective Reduction of CO₂ to C₁ Hydrocarbons

Abstract

Electrocatalytic reduction of CO 2 to energy-rich hydrocarbons such as alkanes, alkenes, and alcohols is a very challenging task. So far, only copper has proven to be capable of such a conversion. We report density functional theory (DFT) calculations combined with the Poisson−Boltzmann implicit solvation model to show that single-atom alloys (SAAs) are promising electrocatalysts for CO 2 reduction to C 1 hydrocarbons in aqueous solution. The majority component of the SAAs studied is either gold or silver, in combination with isolated single atoms, M (M = Cu, Ni, Pd, Pt, Co, Rh, and Ir), replacing surface atoms. We envision that the SAA behaves as a one-pot tandem catalyst: first gold (or silver) reduces CO 2 to CO, and the newly formed CO is then captured by M and is further reduced to C 1 hydrocarbons such as methane or methanol. We studied 28 SAAs, and found about half of them selectively favor the CO 2 reduction reaction over the competing hydrogen evolution reaction. Most of those promising SAAs contain M = Co, Rh, or Ir. The reaction mechanism of two SAAs, Rh@Au(100) and Rh@Ag(100), is explored in detail. Both of them reduce CO 2 to methane but via different pathways. For Rh@Au(100), reduction occurs through the pathway *CO → *CHO → *CHOH → *CH + H 2 O (l) → *CH 2 + H 2 O (l) → *CH 3 + H 2 O (l) → * + H 2 O (l) + CH 4(g) ; whereas, for Rh@Ag(100), the pathway is *CO → *CHO → *CH 2 O→ *OCH 3 → *O + CH 4(g) → *OH + CH 4(g) → * + H 2 O (l) + CH 4(g). The minimum applied voltages to drive the two electrocatalytic systems are −1.01 and −1.12 V RHE for Rh@Au(100) and Rh@Ag(100), respectively, at which the Faradaic efficiencies for CO 2 reduction to CO are 60% for gold and 90% for silver. This suggests that SAA can efficiently reduce CO 2 to methane with as small as 40% loss to the hydrogen evolution reaction for Rh@Au(100) and as small as 10% for Rh@Ag(100). We hope these computational results can stimulate experimental efforts to explore the use of SAA to catalyze CO 2 electrochemical reduction to hydrocarbons.

Electrocatalytic Alloys for CO2 Reduction

“…[57] This study validated the CO* adsorption energy to be ag ood descriptor for the charget ransfer of intermediate products and discounts the volcanop lot relationship thati s widely used as ag uideline for tuning catalysts electivity.H ead-Gordon,B ell, and co-workers calculated single atoms (Cu, Ni, Pt, Pd, Cu, Rh, and Ir) added to gold and silver to converge on alloys containing Co, Rh, and Ir as particularly promisingc andidates for experimental verification. [58] 4.1. Compositional survey…”

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

“…Thermodynamically,the selectivity is decided by the competitive adsorption of the two initial hydrogenation intermediates,C OOH* for the CO 2 RR, and H* for the HER. [18,19] Thestronger adsorption of COOH* will contribute to suppressing the HER since the active sites can be occupied by COOH* instead of H*. Forcases where the adsorption of H* is stronger,t he selectivity for carbonaceous products will be inhibited.…”

Single‐Atom Catalysts of Precious Metals for Electrochemical Reactions

“…Head‐Gordon et al., using DFT calculations, reported that single‐atom alloys, where isolated single‐atoms of Co, Rh, or Ir are located at the surface of Au or Ag, can be promising electrocatalysts for CO 2 reduction to C1 hydrocarbons, such as methane or methanol . The single‐atom alloys favored the formation of OHC* or HOC* over H*, suppressing H 2 production.…”