The catalytic selectivity of an electrochemical process can be greatly affected by the supporting electrolyte’s cations. Cations influence catalysis through a variety of mechanisms: For example, the strong electric fields in the vicinity of cations can affect reaction rates of electrode processes. Cations can further block active sites and impact the structure of interfacial water, which is a reactant in many technologically interesting processes such as carbon dioxide reduction. To effectively steer the selectivity of an electrocatalytic process by means of cation effects, it is essential to determine the principal mechanisms that give rise to observed catalytic selectivity. Using the aqueous electrochemical reduction of CO to hydrocarbons on Cu electrodes as a model reaction, we comprehensively evaluate the relative influence of these different mechanisms on the selectivity of this process. To this end, we employ surface-enhanced infrared absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS). Using SEIRAS and a series of tetra-alkyl ammonium cations, we have determined how cation size controls the strength of the interfacial field, the CO coverage on the electrode, and the hydration state of the CO adlayer. We will discuss the relative influence of these interfacial properties on the hydrogen and ethylene production rates as observed with DEMS. Using mono- and divalent cations, we have further explored how the charge density of cations controls the structure of interfacial water. We will discuss the impact of the interfacial water structure on hydrogen and hydrocarbon evolution.

Controlling the selectivity of electrochemical carbon monoxide reduction via cation-induced restructuring of interfacial water

2019 Spring National Meeting

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