Hydrocarbon Selectivity in CO and CO 2 Reduction on Al–Cu Single‐Atom Alloy Electrocatalysts: Effects of Potential, pH, and Facet

Electrochemical carbon dioxide (CO 2 ) and carbon monoxide (CO) reduction reactions (CO (2) RR) are promising routes for carbon utilization. Previous work unraveled Al–Cu single‐atom alloys to be thermodynamically favorable for CO 2 RR. Here, we explore the kinetics of acidic CO (2) RR to C 1 products on Al–Cu(111)/(211) using first principles. We consider pathways involving CHO, COH, and HCOO intermediates. Ab initio molecular dynamics simulations provide insights into catalyst stability and interfacial water structure. Microkinetic modeling elucidates potential‐ and pH‐dependent selectivity trends on Al–Cu(111), indicating that H 2 evolution is suppressed. For CO 2 reduction, HCOOH dominates across potentials and pH , with hydrogen evolution competing at pH 0. In contrast, CO reduction yields higher current densities, with CH 3 OH prevailing at pH . The CHO pathway exhibits a high activation barrier for CH 4 due to protonation/deoxygenation of CH 3 O, leading instead to CH 3 OH. The COH pathway, though less thermodynamically favored, shows kinetic superiority, with COH dehydroxylation as the rate‐determining step (RDS) for CH 4 formation. This RDS, when analyzed over the stepped Al–Cu(211), has a lower barrier by 0.62 eV. These results highlight the influence of reactant species, electrochemical conditions, and material faceting on catalytic performance, offering insights into tuning selectivity for desired C 1 products.