Potential-Dependent CO Electroreduction Pathways on Cu(111) Based on an Improved Electrode/Aqueous Interface Model: Determination of the Origin of the Overpotentials.

Potential-dependent CO electroreduction pathways on Cu(111) are systematically studied with the aim of applying an improved electrode/aqueous interface model in this paper. The results indicate that our present defined CHO and CHOH pathways may be able to parallelly take place at low overpotentials. Notably, the applied potentials will not alter the optimal CO reduction mechanisms. However, the presence of high overpotentials makes CO electroreduction more favorable, thus explaining why high overpotentials at experiments are required during CO electroreduction on Cu. Based on the potential-dependent energetics, the results suggest that COOH and CHO intermediates may be unstable at low overpotentials, in which COOH can easily change back to CO and CHO can easily change back to CO, thus preventing CO electroreduction. However, the high overpotentials will facilitate the formation and further electroreduction of CO and CHO. Thus, we can speculate that CO formation and then further electroreduction into CHO are the possible potential-limiting steps during CO electroreduction, which are regarded as the origin of experimentally observed high overpotentials. The present comprehensive understanding on CO electroreduction pathways can provide theoretical guidelines for efficiently designing Cu-based alloy electrocatalysts operated under the conditions of low overpotentials.