Surface-Adsorbed CO as a Molecular Probe for the In-Situ Characterization of Electrocatalytic Interfaces

Abstract

The properties of electrified interfaces, such as surface structure of metal catalyst, local pH, coverage of surface-adsorbed intermediates, interfacial electric field, and water structure, influence the activity and selectivity of electrocatalytic reactions. Because these interfacial properties often influence each other and undergo changes with applied potential, it is very challenging to identify the key characteristics of the interface that directly modulate electrocatalytic reactions. In this thesis, we demonstrate in-situ probing of electrochemical interfacial properties by employing surface-enhanced infrared (IR) absorption spectroscopy (SEIRAS) in conjunction with surface-adsorbed CO (COads) as a molecular probe of the Cu/aqueous electrolyte interface. This interface shows potential for the reduction of CO2 and CO to a wide variety of hydrocarbons. The CO and CO2 reduction reactions (CO/CO2RR) feature COads as an intermediate; therefore, this interface is conveniently probed by COads. In the first part if this thesis, we focus on investigating the dynamics of the surface morphology of the electrode during electrocatalysis. We found that the surface morphology of polycrystalline Cu undergoes reconstructions during CO/CO2RR. We determined that these reconstructions can be induced by COads and the local pH. As a result of the surface reconstructions, new specific surface sites form that can effect catalytic activity. For example, we detected an electrochemically inert COads population that appears as a result of reconstruction processes. Further, to form a rigorous connection between the product formation and the atomic-level surface morphology of rough polycrystalline Cu electrodes, we combined SEIRAS with differential electrochemical mass-spectrometry (DEMS). We established the potential-dependence of the line shape of the C≡O stretch band as an indicator of the atomic-level surface morphology. The last part of the thesis focuses on the determination of properties of the electrochemical double layer. Specifically, we elucidated the effects of cation identity on the electrochemical double layer. By evaluating the C≡O stretch frequency in the presence of alkali metal cations (Li+, K+, and Cs+), we determined that the promotion of the CO reduction reaction is associated with a cation-dependent interfacial field.