Thesis advisor: Matthias M. Waegele / The electrocatalytic interface between a metal electrode and its electrolyte constitutes a complex reaction environment involving binding sites on the electrode surface and various molecular components on the liquid side of the interface. To add to the complexity, this environment can evolve during catalysis as a function of the applied potential, pH, supporting electrolyte identity and current density. Therefore, breaking down the impact of the individual components on the catalytic interface requires in situ techniques. In this thesis, employing in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), we elucidated some of the molecular components of the electrocatalytic interface that influence CO2 reduction. We applied this technique to study the reaction on polycrystalline Cu and Au electrodes. In the first part of this thesis, using surface-adsorbed CO, COads, a reaction intermediate during the reduction of CO2 to hydrocarbons, as a vibrational probe to study the evolution and speciation of the Cu electrode surface under alkaline pH conditions. We showed that the electrolyte pH and the applied potential drive irreversible reconstruction of the Cu surface to favor the binding of multiply bonded CO (CObridge). We found CObridge to be electrochemically inert. Instead, the singly bound COatop is the primary on-pathway CO intermediate for further reduction to hydrocarbons. In another study, we analyzed the vibrational band of the COatop intermediate to observe how the presence of molecular additives in the form of N-arylpyridinium-derived films impacts the selectivity for CO2 reduction. We found that certain types of N-arylpyridinium-derived films block adsorption of COatop on undercoordinated Cu sites, thereby halting hydrocarbon formation. Other N-arylpyridinium-derived films do not impact the COatop population, but provide a porous barrier between the electrode and electrolyte that increases the interfacial pH. We found that the increase in interfacial pH is likely responsible for the observed suppression of H2 and CH4 formation in comparison with the respective formation rates of these products on unmodified Cu electrodes. In Chapter 5 of this thesis, we investigated to what extent anions of the supporting electrolyte control the adsorption of COatop. This intermediate plays a central role in the mechanisms of CO2 reduction. Under 1 M anion concentration, we found that specifically adsorbed Cl- destabilizes CO binding through ligand effects. Hydrated SO42- and ClO4- block a fraction of COatop sites. Under 10 mM anion concentration, the identity of the anion did not affect COatop adsorption. This study demonstrates that the identity and concentration of anions can affect COatop adsorption in complex ways. In the final part of this work, we focused on the effects of alkali metal cations on CO2 reduction. We determined the surface concentration of alkali metal cations on Au electrodes (that is, the population of specifically adsorbed alkali metal cations). We probed the surface concentrations by using the CH3 deformation band of the organic cation tetramethylammonium (methyl4N+) as a vibrational probe of the electrochemical double layer. We found that the concentration of the alkali cations at the electrode surface is dependent on the cation’s free energy of hydration. The rate of CO2-to-CO correlates with the measured surface concentration of the alkali metal cation. The ability of a cation to undergo partial dehydration therefore is a critical factor in the cationic promotion CO2 reduction. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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The novel compound [Ru(bpy)(dpb)–(PFâ )â was synthesized, in a manner similar to the literature synthesis of [Ru(bpy)(dpq)â (PFâ )â . For the sake of completeness, the related analogs, [Ru(bpy)â (dpb)](PFâ )â , [Ru(bpy)â (dpq)](PFâ )â and [Ru(bpy)(dpq)â ](PFâ )â were also synthesized. Alumina adsorption chromatography was used for purification purposes. Liquid secondary ion mass spectroscopy was used to confirm identity of compounds. The new compound contained 1% electroactive impurity as determined by OSWV. Spectroelectrochemical studies were conducted with both a bulk H-cell and a ~0.2 mm pathlength, optically transparent thin layer electrode (OTTLE) cell. High reversibility (a 99%) is possible with dilute solutions (ca 10⠻⠴ M) and the OTTLE cell as compared to ca 50% with the H-cell. Spectroelectrochemical data supported the following electronic transitions for the new compound [Ru(bpy)(dpb)â ](PFâ )â : (1) the Ru (dÏ ) â dpb MLCT at 552 nm, (2) a d â d at 242 nm, a bpy Ï â Ï * at 285 nm. (3) The location of the Ru (dÏ ) â bpy MLCT peak is obscured by shoulders from 390-420 nm. (4) The strong peak at 316 nm may be dpb Ï â Ï â *, the location of the lower energy intraligand dpb Ï â Ï â * is uncertain. Upon oxidation of the metal center, no LMCT was observed within the UV-VIS range. This is in direct contrast to the results of Gordon et al. This author hypothesizes that their LMCT found in the visible region was actually the result of incomplete electrochemical conversion and that a LMCT should be seen in the NIR. The spectroelectrochemical properties of [Ru(bpy)(dpq)â ](PFâ )â were also presented for the first time. These results indicated that the 256 nm transition was d â d and not bpy Ï â Ï â * as suggested by Rillema et al. / Master of Science

At Cameco mine sites in northern Saskatchewan, naturally occurring elements of concern (EOC) such as As, Ni, Mo, and Se are present in uranium ore bodies. Ferrihydrite (Fh) is found in tailings management facilities (TMF) and is known to sequester arsenates and arsenites. Fh is known to be metastable and undergo phase transformations to goethite (α-FeOOH) and hematite (α-Fe2O3). Reductive conditions are known to be a driving force in Fh transformation and the release of adsorbed As species from the surface. This study uses electrochemistry to control reductive potentials applied to Fh adsorbed As species. Electrochemistry was coupled with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to determine the behaviour of adsorbed arsenate and arsenite on the Fh surface. The potentials required to desorb As(III) and As(V) from the Fh surface were negative enough to cause the reduction of water, thus increasing the pH of the solution through the generation of OH-. In order to measure the extent of the pH change a miniature palladium/palladium oxide pH sensor was fabricated in order to make in-situ pH measurements during spectroelectrochemical studies. Additionally, in-situ solution potential (Eh) measurements were made during potential control. It was found that potential induced pH and Eh changes were significant enough to release arsenite from the Fh surface. Arsenate was also found to desorb from Fh during the application of reductive potentials though successive deprotonation leading to a totally deprotonated As(V) species.

The level of information provided by electrochemical measurements can be substantial as evident by the use of electrochemistry in varied disciplines spanning from materials research to cellular biochemistry. However, electrochemistry on its own does not provide direct information concerning redox induced changes in molecular structure. This information can only be elucidated by coupling spectroscopic and/or separation techniques with traditional electrochemical methodologies. In principle, infrared (IR) spectroelectrochemistry (SEC) is ideal for such studies but in practice coupling IR spectroscopy and electrochemistry are often experimentally incompatible. Since the inception of in-situ IR SEC techniques in the 1980’s, two competing methodologies (using either external- or internal- IR reflection geometries), were developed to deal with the two major challenges associated with IR SEC (strong infrared absorption of the electrolytes and weak analytical signals). The primary focus of this thesis is the successful advancement of IR SEC techniques through the implementation of synchrotron infrared radiation with ultramicroelectrodes (UMEs; electrode diameters < 25 µm) to study spectroelectrochemical processes on the microsecond time scale. Several examples using Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS) are presented including the adsorption of dimethylaminopyridine (DMAP) on gold substrates and the proton-coupled electron-transfer (PCET) kinetics of electrochemically-active 1,4-benzoquinone terminated self-assembled monolayers (SAMs). These studies highlight the benefits of coupling electrochemistry and infrared spectroscopy. For instance, in-situ spectroscopic evidence shows that small amounts of DMAP’s conjugate acid (DMAPH+) adsorb on gold electrodes in acidic electrolytes and at negative potentials. This result was not forthcoming from previous electrochemical measurements and was only realized through in-situ SEIRAS. Finally, the largest contribution in advancing in-situ IR SEC methodologies was through the development of utilizing synchrotron infrared radiation on UMEs to study fast electrochemical processes. This work was technically very challenging and emphasized the interfacing of an electrochemical cell containing an UME with fast infrared data acquisition techniques (i.e. rapid scan and step-scan interferometry). The use of a prototypical electrochemical system, i.e. the mass-transport controlled reduction of ferricyanide, indicate that at short times the spectroscopic signal closely matches the electrochemical signal but at long time scales it deviates due to edge effects associated with the diffusion environment of the UME.

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