Curtis Berlinguette

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Electrochemical CO₂ reduction is a means of using captured CO₂, water, and electricity to produce carbon-based chemicals and fuels. The CO₂ reduction reaction (CO2RR) provides access to a range of products including carbon monoxide (CO), which can be further upgraded into methanol and diesel. The CO2RR therefore provides a path to generating liquid fuels from captured CO₂, provided that electrochemical reactors (electrolysers) capable of efficiently reducing CO₂ into CO at high rates can be developed. In this thesis, I demonstrate how to design materials for electrolysers that efficiently reduce CO₂ into CO.This thesis first describes how to prepare anion-exchange membranes that attenuate water transport in CO₂(g)-fed electrolysers. Prior to this work, CO₂(g)-fed electrolysers suffered from poor durability due to excess water accumulating in the cathode. Here, I demonstrate that water transport to the cathode can be attenuated by increasing the water sorption or decreasing the thickness of membranes. These modifications enabled a 37% increase in CO formation and 450 mV decrease in cell voltage at 200 mA cmˉ² relative to a reference electrolyser.I then show how cathode fabrication methods affect the efficiency of CO₂(g)-fed electrolysers. CO₂(g)-fed electrolyser cathodes are commonly prepared by depositing dispersions of catalysts and polymeric binders (ionomers) onto porous substrates. This work resolves how the dispersion solvent modulates the surface area, hydrophobicity, and wettability of catalyst layers, which modulate CO2RR efficiency in electrolysers. My results show that the dispersion solvent identity can cause > 50% deviations in the faradaic efficiency for CO at 200 mA cmˉ² between compositionally identical electrodes.I then investigate how to increase the CO2RR activity of Ag cathodes for KHCO₃(aq)-fed electrolysers. The use of KHCO₃(aq) feedstocks bypasses energy intensive CO₂(g) separation steps, but also increases H₂O reduction activity. Here, I show that CO2RR activity can be selectively increased by functionalizing the Ag cathode surface with methylimidazolium. This functionalization increased CO₂RR activity by 10-fold in an electrochemical cell, and increased CO formation by 30% in a KHCO₃(aq)-fed electrolyser. I used operando Raman spectroscopy to show that methylimidazolium adsorbs to the cathode during electrolysis in an orientation which may stabilize intermediates.

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Electron transfer reactions in solution and electron transport in solid-state devices often involve electron transfer events between distinct molecules or otherwise through interfaces between disparate materials. The performance of electronic materials and redox catalysts relies in part on fast intermolecular electron transfer. The electronic coupling (HDA), between electron donors and acceptors is a crucial factor in determining the rate of electron transfer reactions, yet, among the many factors influencing intermolecular electron transfer kinetics, this property is arguably the most challenging to reliably engineer. While it is well understood that HDA can be influenced by the nature of weak intermolecular interactions between the reactants in intermolecular electron transfer reactions, universal structure-property relationships that can be applied to modulate HDA through any interaction in any situation have yet to be developed. For ground-state intermolecular electron transfer reactions, HDA of a reacting donor-acceptor pair in their reactive geometry can be approximated from the overlap integral between their frontier molecular orbitals. In this thesis, I show that this approximation can serve as a useful intuitive tool for researchers designing high-performance electronic materials. In order for a particular intermolecular interaction to increase HDA, it is necessary that the frontier molecular orbitals of the electron donor and acceptor are significantly delocalized onto the atoms involved in that reaction. Moreover, the extent to which those atoms are involved in the frontier molecular orbitals can serve as a rough quantitative predictor of the relative magnitude of HDA through those interactions. I demonstrate, through the use of this principle, how careful design of molecular electron acceptors can accelerate the rate of iodide oxidation through non-specific chalcogen-iodide interactions or through halogen bonding interactions. A surprising consequence of this research was the discovery that halogen bonds can involve not just a σ-symmetric covalent component, but a π-symmetric component as well. Experimental evidence of this π-covalency in a halogen bond and the potential implications of this discovery are discussed in the final chapters.

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Clean energy materials are most frequently used in electrochemical devices such as solar cells, fuel cells, and electrochemical reactors. These devices have exponentially larger materials spaces that must be optimized in comparison to a single component. This increased complexity is due to the intermolecular interactions that arise at the interfaces between materials in these devices. The performance of these devices is determined by this interfacial chemistry. Both the characterization and control of these interfaces is required, for a knowledge-based approach to device optimization. Techniques that characterize the interfaces of materials in fully functional devices are, therefore, attractive. In Part 1, I show that dye-sensitized solar cells can be used as a characterization tool to probe interfacial interactions. I am able to manipulate the strength of a halogen-bonding interfacial interaction by exchanging a single atom, and consequently control the performance of the electrochemical device.Most scientific disciplines use automation to accelerate discovery in such large experimental spaces. Laboratory automation has yet to be extensively used in materials science. The diverse experimental workflows and extreme experimental conditions used in materials science often require highly customized automation. Flexible automation is the use of robotics to create reconfigurable, automated experiments, which has recently been enabled by the emergence of safer, cheaper, and more user-friendly robotics. Self-driving laboratories are one such opportunity for materials researchers to use flexible automation to move towards autonomous, hypothesis-driven experimentation. Self-driving laboratories are robots controlled by decision-making algorithms that can autonomously plan, execute, and learn from materials science experiments. In Part 2, I introduce Ada: our self-driving laboratory built with flexible automation for automated material discovery and optimization. I show that Ada can accelerate rapid materials discovery and has been successfully deployed to three different materials projects.

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To satisfy the evolving needs of the many industries that employ thin-film materials, new materials and deposition methods are continually being optimized. These optimizations are often slow and empirical because thin-film materials and deposition methods are complex. In this thesis I develop a new tool for accelerating the optimization of thin-film materials: a self-driving laboratory (SDL). This SDL consists of a suite of automated film synthesis and characterization stations linked together by robots and controlled by an experiment-planning algorithm. This SDL optimizes thin-film materials by iteratively planning and executing film synthesis experiments in a fully autonomous loop. I first demonstrate the SDL by using it to autonomously maximize the hole mobility of films of spiro-OMeTAD, a p-type organic semiconductor used in perovskite solar cells. The SDL automatically deposited films containing varying amounts of a dopant, annealed these films for varying durations, and then characterized the films. The SDL identified the doping ratio and annealing time that maximize the hole mobility by performing 35 cycles of iterative experimentation under the control of a Bayesian optimization algorithm. This study showed that an SDL can autonomously optimize film composition and processing parameters without ongoing human intervention. I then upgrade the SDL to optimize combustion-synthesized palladium films for multiple objectives simultaneously. Under the control of a multiobjective Bayesian optimization algorithm, the SDL autonomously identified a range of combustion synthesis conditions yielding optimal trade-offs between the conflicting objectives of conductivity and annealing temperature for drop-cast films. Simulated optimization runs indicated that the self-driving laboratory achieved this result in 10 times fewer experiments than would have been required using a grid search. The combustion synthesis conditions identified by the self-driving laboratory enable the spray coating of uniform palladium films with moderate conductivity (1.1E5 S/m) at 191 °C. Spray coating at 226 °C yields films with conductivities (2.0E6 S/m) comparable to those of sputtered films (2.0 to 5.8E6 S/m). This work shows how a self-driving laboratory can efficiently identify film synthesis conditions yielding optimal trade-offs between conflicting objectives.

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The CO₂ reduction reaction (CO2RR) is a means of producing chemicals and fuels using waste CO₂ instead of fossil fuels. Carbon monoxide (CO) is an appealing target product because it can be converted to carbon-neutral diesel and methanol using established industrial chemistry. However, a source of purified gaseous CO₂ is often a prerequisite to forming CO at high rates in a low-temperature electrochemical reactor (“electrolyser”). This feedstock of CO₂ for the electrolyser is typically produced using >100 kJ mol⁻¹ thermal energy from fossil fuel combustion. In this thesis, I show that liquid bicarbonate solutions produced by reactive carbon capture can be converted into CO without the need to thermally isolate gaseous CO₂ upstream of the electrolyser.In this thesis, I first investigate the conversion of aqueous bicarbonate (HCO₃–(aq)) solutions into CO in an electrolyser composed of nickel anode, bipolar membrane, and silver cathode. Before this work, it was not known whether liquid bicarbonate solutions could be converted into CO at product formation rates (current densities) greater than 100 mA cm⁻². Here, I demonstrate an electrolyser design that reacts protons with bicarbonate to form CO₂ in situ at the membrane|cathode interface in the electrolyser. This CO₂ intermediate is reduced to the CO product at the silver cathode surface.I then demonstrate silver electrodes that enable electrolysis of bicarbonate solutions into CO at product formation rates that rival gas-fed CO₂ electrolysers. While hydrophobic cathodes yield high CO formation rates in gas-fed CO₂ electrolysers, my experiments show that hydrophobic electrodes are not suitable for bicarbonate electrolysers, which use liquid feedstocks. I demonstrate that hydrophilic silver cathodes enable faradaic efficiencies for CO formation of 82% at 100 mA cm⁻², which is higher than the 37% achieved with the hydrophobic cathodes.I then developed a physical model that simulates the acid-base and electrochemical reactions in the cathode of the bicarbonate electrolyser. The model is validated with experimental results and is used to elucidate the rate limiting step in the bicarbonate electrolyser. This model confirmed my experimental results which showed that the rate of in-situ CO₂ formation governs the rate of CO formation.

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CO₂ reduction in electrolysers is a promising method to produce carbon-neutral chemicals and fuels. A significant challenge for commercializing this technology is the development of durable and efficient catalysts that selectively generate a single product. Molecular electrocatalysts can potentially mitigate this challenge because of the acute synthetic control over the electronic environment of the active site. These catalysts, however, are typically tested and studied at rates and voltages orders of magnitude lower than what is required for industrial operation.This thesis first demonstrates that a molecular electrocatalyst, cobalt phthalocyanine (CoPc), can mediate fast and selective CO₂-to-CO conversion in a flow cell. This process is made possible by the direct supply of gaseous CO₂ to a customized flow cell architecture. The configuration accommodated current densities exceeding 150 milliamperes per square centimetre (mA/cm²). After this proof-of-concept work, this thesis investigates the mechanism of CO₂ reduction mediated by CoPc molecular catalysts by the use of a marriage of electrochemistry and operando Raman spectroscopy. The mechanistic insights provided clear design principles for immobilized molecular catalysts used in a flow cell. This study also demonstrates that catalyst aggregation is a deciding variable with regard to the distribution of active species in a flow cell.Finally, this thesis studies the CO conversion to higher-value multi carbon product (C₂₊) production mediated by the copper phthalocyanine (CuPc) catalyst layer in a CO electrolyser. A gas diffusion electrode coated with CuPc can effectively electrolyze CO into C₂₊ products at high rates of product formation (i. e., current densities ≥ 200 mA/cm²), and high faradaic efficiencies for C₂₊ production (FEc₂₊; >70 % at 200 mA/cm²). The active species generated during the electrolysis were identified using series of in-situ and ex-situ characterization techniques. These results open the door to use the rich library of metal-complex catalysts accessible in the literature, as well as novel analogues, for efficient CO electrolysis and C₂₊ formation.

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Heterogeneous hydrogenation is an important industrial process widely used in fine chemical syntheses, pharmaceutical, food, and biofuel production. Hydrogenation is performed by combining reactants (H2 gas and substrates) in one reactor, where both react on the same catalyst surface. This combination of reactants complicates understanding the catalytic process because several competing processes will occur on the same catalyst surface. The electrocatalytic palladium membrane reactor (ePMR) is a unique hydrogenation reactor that separates the hydrogen activation from the hydrogenation process. This reactor not only enables hydrogenation to be performed at ambient temperatures and pressures but also provides fine-tuning of the amount of hydrogen supplied (fugacity) by tuning the applied current. This thesis presents a series of work related to the heterogeneous catalytic processes in the ePMR. This thesis first presents the study of electrochemical processes of the palladium electrode. A customized temperature-programmed desorption (TPD) instrument was built to characterize the palladium films electrochemically saturated with absorbed hydrogen (PdHx for x > 0.6). The electrolyte choice is found to affect hydrogen sorption and desorption kinetics on the palladium surface due to the specific adsorption of the anion.The thesis then presents the advantages of ePMR to study the reaction pathway of hydrogenation. The conventional thermochemical hydrogenation process requires high temperatures and pressure, which may lead to morphology change of the catalysts. It also complicates the understanding of hydrogenation because multiple catalytic processes occur on the same catalyst surface. The ePMR enables the hydrogenation at ambient conditions and separates the catalytic process. The hydrogenation pathway of benzaldehyde is successfully resolved on the palladium nanocubes by combining the ePMR and well-defined nanocubes. Finally, the use of ePMR for hydrogen peroxide production is demonstrated. Hydrogen peroxide is a crucial chemical for various applications. The production of hydrogen peroxide is a carbon-intensive process that requires the hydrogenation and oxidation of an intermediate molecule. The direct hydrogenation of oxygen can simplify the infrastructure and decrease the capital cost of the process but is risky for using the mixture of hydrogen and oxygen. The ePMR can supply high-fugacity hydrogen in-situ and overcome these disadvantages.

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The electrochemical conversion of CO₂ into fuels or commodity chemicals is a means to store renewable energy in fuels and chemical products. A CO₂ electrolyzer is an electrochemical flow cell that uses electricity, carbon dioxide, and water to produce carbonaceous products such as carbon monoxide (CO). For electrolytically generated CO to be cost competitive with CO produced by fossil fuel feedstocks, a CO₂ electrolyzer must simultaneously achieve: high product formation rates (current density > 200 mA cm⁻²); high product selectivity (faradaic efficiency > 90%); and high energy efficiency (cell voltage 3.0 V). An understanding of reaction conditions and an optimization of cell components are needed to achieve these performance targets.This thesis details a method to rapidly prototype electrolyzer flow plates by electroplating 3D printed composite conductive plastic parts. The rapidly prototyped flow plates have comparable performance to an all-metal flow plate at half of the cost and 1/7 of the weight. The prototyping methods were utilized to develop an “analytical electrolyzer” that directly measures fluid conditions within an operating cell. Proof of concept work was completed using a PEM water electrolysis cell. The measured temperature and pressure in the analytical cell were in agreement with literature results and simulations.These methods were then applied to a gas-phase CO₂ electrolyzer to quantify water concentration throughout the cathode compartment. Water is a reactant and integral to CO₂ electrolyzer performance. Humidity and temperature measurements were used to produce a mass transport and fluid flow model of the cathode compartment. The model quantified the method and magnitude by which water enters the cathode compartment. The molar fraction of water at the cathodic GDE/membrane interface remains constant under a range of operating conditions (current density = 25-200 mA cm⁻², flow rate = 25-200 sccm, CO₂ feed humidity = 0% or 70%). An increased water flux across the membrane occurred while operating with dry CO₂ feedstocks at higher flow rates and current densities. The increased water flux across the membrane negatively affected CO₂ electrolyzer performance and stability. The techniques and results reported in this thesis will empower the more thoughtful design of electrolyzer cells.

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Hydrogenation is a class of chemical manufacturing widely used for applications including fine chemicals, food, fertilizer, and fuels. Conventional thermochemical hydrogenation requires large amounts of hydrogen gas and heat derived from fossil fuel combustion to enable reaction. This process is highly carbon intensive. In this thesis, I present the electrocatalytic palladium membrane reactor (ePMR) as a technology that can reduce this carbon footprint by producing hydrogenated chemicals using water and renewable electricity. In this architecture, reactive hydrogen atoms are produced from water electrolysis on one side of a palladium membrane. These hydrogen atoms are then transported through the membrane to react with an unsaturated bond of a substrate on the other side. This technology eliminates the use of hydrogen gas and fossil fuels, and operates under ambient temperatures and pressures.In this thesis, I first demonstrate the utility of the ePMR to pair two organic reactions. Electrochemical synthesis generally forms a useful product at one electrode and a waste product at the other electrode. The palladium membrane acts as a physical barrier between the two electrodes, enabling optimized reaction conditions of two reactions simultaneously. I also investigate the effect of catalyst surface area, applied current, and electrolyte on reaction selectivity in the ePMR.I then focus on reducing the palladium content in an ePMR through a supported palladium membrane design. I show that a thin layer of palladium (2 μm) deposited onto a porous support can enable a >20-fold reduction in palladium content compared to palladium foil membranes (25 μm) often used in the ePMR. The supported membrane design enables faster 1-hexyne hydrogenation rates than palladium foil and provides a strategy for designing cost-effective and potentially scalable membranes.Finally, I show that furfural (an important biomass derivative) can be hydrogenated into higher value products, furfuryl alcohol and tetrahydrofurfuryl alcohol at selectivities >84%. I also compare the ePMR to conventional electrochemical hydrogenation reactors. I find that furfural hydrogenation in the ePMR proceeds at higher selectivity, suppresses side product formation, and lowers operating voltages. This work presents an opportunity to decarbonize a >350,000 ton year-1 hydrogenation industry.

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Organic chemicals are the building blocks for plastics, clothing, fertilizers, pharmaceuticals and fuels. Nearly all these materials are manufactured at high temperatures, using fossil fuels to heat the reactors. These processes are resultantly carbon intensive. This thesis presents a technology, called an electrocatalytic palladium membrane reactor (ePMR), that can reduce the carbon impact of chemical manufacturing by using only water and electricity to produce hydrogenated chemicals. This reactor generates reactive hydrogen atoms from water electrolysis, the hydrogen atoms then pass through a palladium membrane to react with an unsaturated feedstock at the opposite surface of the metal. By using an electrochemical driving force, the ePMR can perform hydrogenation without any fossil-derived inputs or high temperatures or pressures.I first focused on the palladium electrode at the center of the ePMR. I investigated how the spacing between palladium atoms influences the rate that hydrogen is produced during electrolysis, and also the amount of hydrogen that absorbs into the palladium electrode. I designed an electrochemical cell that applies mechanical strain to the palladium lattice and used electrochemical measurements to show that tensile strain increases the hydrogen production rate, and decreases the amount of hydrogen that absorbs into the lattice.I then focused on increasing the rate of hydrogenation in an ePMR through electrochemical flow cell design. I developed a flow reactor to enable up to 15-fold faster hydrogenation rates than can be achieved in a conventional palladium membrane reactor. This flow cell also enabled me to study how hydrogen in the membrane influences reaction rate and selectivity. Hydrogenation rate is proportional to the hydrogen loading in the membrane, while selectivity for the alkene intermediate is inversely proportional to hydrogen content.Finally, I show that hydrogenation reactivity can be influenced by depositing secondary metals on the hydrogenation surface of the palladium membrane. This approach was designed to increase reactivity for harder-to-reduce C=O functionalities. I found that thin films of iridium, gold and platinum all increase hydrogenation rates for carbonyl groups, while only platinum increases hydrogenation rates for C=C unsaturations. This work provides a new catalyst design strategy for tailoring reactivity in the ePMR.

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Electrochemical reduction of CO₂ to value-added liquid fuels and chemical feedstocks is a sustainable approach to off-peak electricity utilization. The propagation of a CO₂ value chain through capture-conversion technology is bottlenecked by a lack of systems capable of catalytic CO₂ conversion with the efficiency, selectivity, robustness, and economic viability relevant to industry. The design of a CO₂ electrolyzer that can operate at current densities (J) > 200 mA/cm² , Faradaic efficiencies (FE) > 85%, voltages 3 V is germane to this challenge. Improving the efficiencies, selectivities and current densities of CO₂ electrocatalytic systems are of scientific, environmental, and economic importance. In this thesis, I first demonstrate the development of a flow reactor that utilizes gas-phase CO₂ to achieve higher current densities (J = 200 mA/cm²) than is possible with conventional aqueous-fed systems. I use a silver catalyst dispersed on a gas diffusion layer to produce CO with high selectivity ( > 50%). I deploy a bipolar membrane which allows the use of non-corrosive conditions on either electrode, thereby prolonging cell lifetime.I then detail the design and use of an analytical device to compare the voltages for different CO₂ flow reactor architectures to identify which cell components should be optimized to most effectively lower the overall cell voltage. Analysis of the voltages across the components of three different flow reactor configurations highlights that the reactions at the anodes and cathodes are relatively efficient and that much of the voltage loss occurs at the membran. These results illuminate that a better understanding of membranes and the membrane-catalyst interface is needed.Finally, I demonstrate the incorporation of a molecular catalyst into a CO₂ flow reactor for efficient conversion of CO₂ to CO. Molecular catalysts are known to have high activity for the CO₂ reduction reaction but typically at low rates of conversion (i.e., 30 mA/cm²). In this work, I show that a widely available molecular catalyst, cobalt phlalocyanine, can mediate CO₂ to CO formation in a flow reactor with high conversion rates commensurate with solid-state metal catalysts (ie., > 150 mA/cm² and FE > 85%).

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Hydrogenation reactions are a widely-used class of catalytic transformations but the reactions require high-pressure H₂ gas and specialized equipment for safe handling. Hydrogenation with protons as a hydrogen source (electrocatalytic hydrogenation, ECH) overcomes this challenge but the substrate scope is limited to reactants that can be solubilized in protic conditions. In this thesis, a palladium membrane reactor is used to perform hydrogenation reactions with protons in any desired solvent. Palladium is semi-permeable for monoatomic, reduced hydrogen atoms so protons can be reduced at one side of the palladium, diffuse through the membrane and hydrogenate an unsaturated substrate on the other side of the palladium. The palladium membrane separates electrochemistry from hydrogenation, eliminating the solubility challenge of ECH. In this thesis, I first study hydrogen absorption into palladium. Hydrogen absorption is difficult to quantify because hydrogen is light and has minimal electron density. I demonstrate that coulometry can be an accurate technique to quantify hydrogen absorption when an electrochemical flow cell is used. The flow cell improves the selectivity of coulometry and enables quantification of absorbed hydrogen for a number of different palladium sample types. I then demonstrate the use of a palladium membrane reactor to pair two organic reactions together. Electrochemical reactions often form one product of value and one waste product. The palladium membrane acts as a dense barrier between the anode and cathode, enabling reaction of two organic substrates simultaneously. I also compare palladium membrane reactions to ECH reactions. I find that hydrogenation with a palladium membrane reactor increases reaction rates, changes the possible product distribution and lowers operating voltages. Finally, I study the use of the palladium membrane reactor for deuteration. Deuterated pharmaceuticals are of growing interest because of their increased half-lives. I find that the membrane reactor forms C–D bonds from an inexpensive and reusable D₂O starting material. The method has high site-selectivity and deuterium incorporations, and can be incorporated into a drug synthesis pathway.

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Photoelectrochemical and electrochemical cells drive redox reactions by electricity with and without light, respectively. Water splitting is a widely-studied electrolytic reaction, where oxygen and hydrogen are produced at the anode and cathode, respectively. This technology, however, is limited by the relatively low value of products. The anodic production of oxygen usually requires a significantly higher electrical potential than the theoretical potential and actually holds very little economic value. The product of cathode reaction, hydrogen, may also be a poor target product because the hydrogen made by water electrolysis costs twice as much as the hydrogen extracted from fossil fuels in most markets. Therefore, a better selection of reactant and target product is required to make a value-added photoelectrochemical or electrochemical reaction.I show herein that the challenges for anode reaction in a photoelectrochemical cell can be overcomed by two strategies: lowering the amount of electricity required to produce oxygen; or simply driving alternative chemistry that forms products with higher value than oxygen. A bismuth vanadate (BiVO₄) photoanode is used to develop these two strategies. The photoelectrochemical activity of BiVO₄ is improved (i.e. a lower potential is required to drive water oxidation) by exposure to ultraviolet light radiation. I then use this BiVO₄ photoanode to drive alternative anodic reaction, organic oxidation, and generate organic products that are more valuable than oxygen. A variety of organic transformations are demonstrated on BiVO₄ photoanode, including alcohol oxidation, C-H oxidation and lignin decomposition.I also study an alternative cathode reaction, CO₂ reduction, to replace hydrogen evolution reaction. I demonstrate that pairing cathodic CO₂ reduction with anodic organic oxidation in a single electrochemical cell can make valuable carbon products on both electrodes. I also question a presupposition in many previous CO₂ reduction studies that CO₂ is the best (or even the only) carbon species for cathodic reduction. The direct reductions of bicarbonate and carbonate into CO are demonstrated in an electrochemical flow cell without CO₂ gas feed, which bypasses the energy-intensive step to first thermally extract CO₂ gas in carbon capture and utilization process and suggests bicarbonate/carbonate might be a better cathode reactant than CO₂.

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The conversion of electrical energy derived from clean, renewable, and intermittent sources such as wind and solar into transportable and storable fuels is a means of matching energy supply and demand. Effective electrocatalysts can facilitate these conversions in an economical manner. Our group has developed photodeposition techniques for synthesizing amorphous thin-film metal oxide electrocatalysts. The thicknesses of amorphous metal oxide films were determined by cross-sectional scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). XRF measurements recorded on the films provided a strong linear correlation with the thicknesses determined by cross-sectional SEM. The electrochemical surface area (ECSA) determined by double-layer capacitance measurements did not universally show a linear relationship with film thicknesses. These results highlight the limitations of using ECSA to determine electrocatalyst film thickness. The noninvasive XRF technique is demonstrated to be a superior method for reporting on the thickness and loadings of thin metal oxide films. XRF measurements were made on iron-nickel oxy/hydroxide (FeNiOx) films that are widely known to mediate the oxygen evolution reaction at modest current densities (10 mA cm-²). These measurements enabled the determination of the electrochemical stability and metal composition of these electrocatalyst films when subjected to sustained electrolysis in strong base at a current density J = 200 mA cm-². Most of the iron in the film was liberated during the first 24 h of electrolysis and deposited on the cathode. These results show that one must account for the instability of this mixed-metal composition when drawing structure-property relationships and when considering the scale-up of electrocatalysts.Finally, modifications to the photodeposition technique are demonstrated that enables access to metal and metal alloy thin films. Silver and copper are widely studied metals for catalyzing the CO₂ reduction reaction (CO₂RR), yet studies of Ag-Cu alloys are rare due to the immiscibility of the metals. I report that our photodeposition procedure provides access to Ag-Cu alloys at ambient pressures and temperatures. Our photodeposition procedure is shown to furnish metastable alloys with ~10 atomic weight % (at-%) copper incorporated into the silver lattice. These results provide proof that photodeposition can be used to access kinetic phases of alloys.

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Over six decades of photovoltaic research have led to the emergence of a highly efficient technology called perovskite solar cells (PSCs). Despite the recent sharp rise in power conversion efficiencies (PCEs) of this technology, PSCs have not yet been deployed at scale owing in part to the unsatisfactory stability of devices. The stability issues are due to the light absorbing layers being susceptible to dissolution and the hole-transport material (HTM) layers undergoing morphological changes under real life conditions. This dissertation seeks to suppress mechanisms of PSC degradation through the design of HTMs.I designed a series of five structurally similar HTMs to study the effect of triphenylamine (TPA) location and number on the thermal stability (i.e., glass transition temperature, Tg) of the HTM layer. My studies demonstrate that where the TPA units are positioned about a spiro-carbon core can shift the Tg upwards of 30 °C. I designed HTMs that can be electrochemically and thermally polymerized to yield an encapsulation layer for the PSC. I demonstrated that the polymerized HTM layer decreases film wettability and can be incorporated into a PSC device.I interrogated a series of three structurally analogous donor-acceptor (D-A) architectures (i.e., monopodal, bipodal and tripodal architectures) to determine the role of molecular structure on the hole mobility of HTMs. From these experiments, I learned that “monopodal” D-A architectures yielded the highest hole mobilities because of the low computed reorganization energy, small polaron stabilization energy and hole extraction potential associated with this HTM.Overall, I demonstrated three mechanisms to suppress either the degradation of the photoactive perovskite layer, the morphological changes to the HTM layer or the instability caused by additives in HTM films. I suggest future design principles to yield stable PSC devices towards the commercialization of this technology.

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