(664a) Intercepting Elusive Intermediates in Cu-Mediated CO Electrochemical Reduction with Alkyl Species

Understanding of the reaction network of Cu-catalyzed CO2/CO electroreduction reaction (CO(2)RR) remains incomplete despite intense research effort. This is at least in part because the rate determining step occurs early in the reaction network, leading to short lifetimes of subsequent surface bound intermediates, the knowledge of which is key to selectivity control. Several extensive reaction networks of the CO(2)RR on Cu have been proposed with ab initio calculations in recent publications, however, most of these pathways, along with many predicted reaction intermediates, have yet been verified due to the lack of suitable experimental techniques.

Herein we first demonstrate that alkyl groups, produced from the dissociative adsorption of alkyl iodides on Cu, can effectively couple with surface intermediates in the Cu-catalyzed CORR. For the first time, elusive C1 and C2 intermediates in the CORR were captured by coupling with the alkyl groups. Combining reactivity data and in situ surface enhanced Raman spectroscopic results, we demonstrate that surface bound alkyl groups are able to couple with adsorbed CO to form carboxylates and ketones via one and two successive nucleophilic attacks, respectively. Leveraging this new chemistry, CHx and C2Hx are intercepted and identified as precursors for methane and n-propanol in the CORR, respectively. We demonstrated reaction pathways leading to methane and C2+ products were not intrinsically orthogonal, and their connection is mainly impeded by low coverages of surface intermediates. The rate of C-C coupling steps in the CORR depends critically on the probability of encounter of the reactants, which makes the introduction of adsorbed alkyl groups especially suitable to intercept surface intermediates involved in the C-C coupling step of the CORR. The strategy proposed in the manuscript that perturbing the reaction of interest by introducing a slightly interacting probe reaction network could be general and informative to mechanistic studies of electrocatalytic reactions.