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.

The utilization of porous materials for electrocatalytic applications has been of high interest due to their high surface area and increase in electrode-electrolyte interface. Metal-organic frameworks (MOFs) are an emerging class of 3-D porous materials consisting of inorganic nodes bound by multidentate organic linkers. MOFs have permanently large surface area, high stability, and the tunability of the structure. The metal source or the organic linker can be swapped to create a material with desirable features. MOFs have been explored for applications in electrocatalysis, conductivity and energy storage. The fundamental charge transfer methods of MOF thin films is discussed and the utilization of these conductive materials for the key reactions in artificial photosynthesis is explored to highlight methods to improve the efficiency of these materials for electrocatalysis. The Morris group has previously shown that charge transfer in MOFs can occur through a redox hopping mechanism in which the charge hops from redox center to redox center through space followed by the movement of a charge balancing ions. In Chapter 2, the charge transfer mechanism within the MOF is further investigated by utilization of spectroelectrochemistry. The incorporation of a redox center, Ru(bpy)2(dcbpy), "RuBPY" where bpy = 2,2′-bipyridine; bpy-(COOH)2 = 5,5′-dicarboxylic acid-2,2′-bipyridine into the UiO-67 framework creates a conductive MOF that is also electrochromic. RuBPY is a deep orange color in the standard RuII state and upon oxidation to RuIII it is pale green. The change in absorption profile of the redox center allows for the rate of oxidation to be determined through absorbance measurements. The material showed minimal change in absorbance upon applying an oxidative potential. The incorporation of a sulfonate group into the backbone of the RuBPY-UiO-67-SO3H MOF allowed for a much higher change in absorbance converting the entire MOF into the oxidized state. The change in level of absorbance indicates that the sulfonate groups improve the conductivity within the pores of the MOF allowing for oxidation of previously electrochemically inaccessible redox centers. The sulfonate groups are thought to break ion pairs of the electrolyte and increase effective electrolyte concentration within the pores. The sulfonate groups' ability to improve the conductivity within the MOF can be further investigated to improve charge transfer through porous materials. The sulfonate groups were again incorporated into the UiO-67 MOF framework for use in electrocatalytic applications by also incorporating the known water oxidation catalyst, RuTPY, Ru(tpy)(dcbpy)H2O. A RuTPY-UiO-67 film had previously shown reactivity as a water oxidation catalyst with improved activity over a monolayer of RuTPY on fluorine-doped tin oxide, FTO. The sulfonate groups were added to create a proton transfer chain that shuttled the generated protons away from the catalytic site to improve reactivity. The incorporation of sulfonate groups again showed improved charge transfer from the MOF materials with the RuTPY-UiO-67-SO3H being 100% electrochemically accessible. The water oxidation capabilities improved giving the material increased oxygen generation upon oxidation of water. The improvement of catalytic activity of RuTPY-UiO-67-SO3H was beyond the increased electrochemical accessibility means the proximal sulfonate groups were aiding in catalysis in some manor. This work highlights the use of multivariate approaches to MOFs to improved efficiency in various applications. The fourth chapter discusses the other half of artificial photosynthesis, CO2 reduction. The known CO2 reduction catalyst, Ni(cyclam), is incorporated into a zirconium-based MOF, VPI-100. The VPI-100 powder was electrochemically deposited onto a glassy carbon electrode and the film was used for electrochemical CO2 reduction into carbon dioxide. The film successfully generated CO as a major product with a faradaic efficiency of 56%. The film was stable under electroreduction conditions and was able to be recycled for continuous production of CO. The final chapter is a review that discusses the utilization of MOFs as photocatalysts for CO2 conversion using only abundant earth metals. While most CO2 catalysts are expensive noble metals, the development of cheap abundant catalytic materials is extremely relevant to a clean energy future. / Doctor of Philosophy / The climate crisis has led to a need to develop more efficient renewable energy sources and novel energy storage devices. Electrochemical systems have shown great promise in providing a clean energy future with developments in lithium-ion batteries, fuel cell technologies, and artificial photosynthesis to produce value added chemicals. The basis of all these electrochemical processes is efficient charge transfer to the necessary components. Metal-organic Frameworks (MOFs) which are crystalline, porous materials made up of inorganic metal nodes connected in a discrete pattern by organic linkers. The three-dimensional nature of the MOFs consisting of connected pore networks has shown great promise to be improved conductive materials and electrocatalysts compared to existing materials. Herein, we exploit the modular nature of the MOFs to incorporate functional groups that improve ion transport and allow catalytic activity for artificial photosynthesis. The work here shows that MOF structures can be further modified to provide even more efficient electrocatalytic behavior to aid in a clean energy future.

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