Fundamental studies of the electrochemical interface using attenuated total reflectance surface enhanced infrared spectroscopy

Abstract

A detailed understanding of the electrical double layer is key to the optimization of heterogeneous electrochemical reactions. A myriad of factors within the double layer can influence reaction rates. This dissertation focuses on several key aspects of the double layer and the resultant effect on electrochemical processes generally, albeit with an emphasis on the electrochemical reduction of CO2. Here we present a broad study of the factors affecting electrochemical activity, including electrode material, potential-dependent solvent geometry, interfacial reactant concentration, potential-dependent interactions between electrode and electrolyte ions, and electrode contamination resulting from various experimental conditions, resulting in both generalized behavior for electrochemical processes and molecular-level reaction networks for CO2 reduction in multiple systems. ☐ To study the electrochemical double layer, we use traditional electrochemical methods coupled with isotopic labeling and attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to probe the effect of the electrochemical double layer on surface-mediated electrochemical reactions. Coupling ATR-SEIRAS with widespread voltammetric techniques and kinetic analysis allows us to selectively probe the electrochemical double layer at the molecular level as a function of electrode potential, giving new insight into electrochemical CO2 reduction and the behavior of the double layer more generally. Throughout the research presented in the following dissertation, we develop numerous new spectroelectrochemical cell configurations to expand the capabilities of this highly surface-sensitive technique and more closely mimic operando electrochemical conditions. Using these techniques we provide new mechanistic insight into the electrochemical reduction of CO2 in bicarbonate on Au and Ag, the pyridine-mediated electrochemical reduction of CO2 on Pt, the potential-dependent reorganization of water in the double layer in acidic and alkaline electrolytes, the interaction between cations, adsorbates, and the electrode surface, interfacial concentration effects on electrokinetics, and the causes and effects of electrode contamination in ATR-SEIRAS studies.