Carbon dioxide capture and utilization technologies are necessary to create a truly circular economy. The electrochemical reduction of carbon dioxide to formate is an appealing carbon utilization... Show moreCarbon dioxide capture and utilization technologies are necessary to create a truly circular economy. The electrochemical reduction of carbon dioxide to formate is an appealing carbon utilization method as it can be performed at room temperature and pressure, it only requires two electrons, and it has a high atom efficiency. This reaction has been known and studied for decades, but no commercial process is currently practiced.This thesis reviews work that has been performed in the field of electrocehmical reduction of CO2 toward formate and reviews how a gas diffusion electrode functions. A gas diffusion layer production method is explored for ways to tune the characteristics of the gas diffusion layer. A design of experiments is used to explore how the catalyst layer can interact with the gas diffusion layer. The best results (100% CE at 400mA/cm2) are scaled-up from 10 cm2 to 200 cm2. Contaminants in an industrial CO2 stream are studied using density funcitonal theory to determine their potential to poison electrocatalysts known to convert CO2 to formate. Show less
To design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide... Show moreTo design the ideal water oxidation catalyst, understanding of the catalytic mechanism and decomposition pathways is essential. The aim of the research described in this thesis is to provide mechanistic insight on the water oxidation reaction catalyzed by homogeneous electrocatalysts and topostulate design criteria for the ideal water oxidation catalyst. Show less
The electrochemical oxygen reduction reaction (ORR) is an essential half-reaction for the utilization of hydrogen as a sustainable fuel, via the conversion of hydrogen to electrons and protons... Show moreThe electrochemical oxygen reduction reaction (ORR) is an essential half-reaction for the utilization of hydrogen as a sustainable fuel, via the conversion of hydrogen to electrons and protons facilitated by the ORR. In the most common fuel cells, the ORR is requires high loadings of non-abundant platinum based catalysts. Inspired by Laccase, a multicopper oxidase able to perform the ORR at a low overpotential, copper complexes have become interesting targets as non-precious metal catalysts for the ORR.In this thesis, the ORR performance of molecular copper catalysts and the involved catalytic mechanisms have been investigated. The previously undetermined electrocatalytic mechanism for the ORR by the Cu(tmpa) copper complex was elucidated. Hydrogen peroxide was shown to play an important role in the catalytic cycle as a reaction intermediate. This has interesting implications for the sustainable electrochemical production of hydrogen peroxide. Furthermore, the reduction of hydrogen peroxide shows striking similarities with Fenton-like reactions observed in copper containing enzymes. Finally, the performance of several different copper electrocatalysts for the reduction of oxygen and hydrogen peroxide was investigated and compared. Show less
Molecular complexes can be used as electrocatalysts for oxygen reduction, water oxidation, and/or hydrogen peroxide production. However, in situ degradation of these catalyst is a major issue. This... Show moreMolecular complexes can be used as electrocatalysts for oxygen reduction, water oxidation, and/or hydrogen peroxide production. However, in situ degradation of these catalyst is a major issue. This dissertations describes the analysis of degradation processes as well as the performance of various molecular electrocatalysts. In addition, complexes have been structurally modified to perform structure-activity studies that could to mechanistic insight. In addition, it is described how molecular catalysts can be beneficial to heterogeneous electrocatalysis as well. Show less
In this dissertation iron-based homogeneous catalysts were synthesized, characterized and investigated for water oxidation activity. The catalysts were studied under electrochemical conditions in... Show moreIn this dissertation iron-based homogeneous catalysts were synthesized, characterized and investigated for water oxidation activity. The catalysts were studied under electrochemical conditions in order to compare the electrochemical approach to the catalysis based on the use of sacrificial oxidants. The mechanisms under which these catalysts operate have been explored with particular attention to the O−O bond formation step. The combination of electrochemical techniques and in situ characterization techniques allowed for the identification of the active intermediates responsible for catalysis. The influence of the presence of water oxidation catalysts in solution on the evolution of carbon dioxide from the surface of a pyrolytic graphite working electrode was also investigated. Overall, the results of this work demonstrate that the combination of in operando and in situ (spectro)electrochemical techniques allows for a complete investigation of the catalytic mechanism of the water oxidation reaction. Show less
The focus throughout this thesis will be on gathering fundamental studies of the detailed structure and composition of the electrode/electrolyte interface effect on the rate and mechanism of key... Show moreThe focus throughout this thesis will be on gathering fundamental studies of the detailed structure and composition of the electrode/electrolyte interface effect on the rate and mechanism of key electrocatalytic reactions. The first part (Chapter 2 and 3) of this PhD thesis is about the studies of the non-Nernstian dependence on pH of the step-related voltammetric peak on platinum surface. The combined experimental and computational studies prove the existence of the co-adsorbed alkaline metal cation (Li, Na, K, and Cs) and hydroxyl at step sites of a platinum electrode. The co-adsorbed alkaline metal cation weakens the hydroxyl adsorption which yielding the anomalous non-Nernstian dependence on pH of the step-related “hydrogen peaks”. The second part starts from Chapter 4 changes first to the study of adsorption processes on a Pd monolayer-modified Pt(111) surface. Chapter 5 deals with the mechanism of electrocatalytic oxidation of formic acid and reduction of carbon dioxide on this Pd monolayer-modified Pt(111) electrode. The work in Chapter 6 explores the effects of electrolyte composition and catalysts surface structure on formic acid oxidation reaction. Show less
This thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special... Show moreThis thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special attention is focused on the interactions between single emitters and GNRs. The idea is to increase the emission of weak emitters by the excellent optical properties of GNRs so that weak light emitters will then be bright enough to be detected and studied individually. We can thus generalize single-molecule fluorescence spectroscopy to weakly emitting species which are currently undetectable by conventional single-molecule spectroscopy. The research is important for extending the scope of single-molecule spectroscopy, which is a powerful technique for understanding the dynamic behaviors at the nanometer scale in biological systems and other materials. Show less
In this dissertation, the synthesis and characterization of a series of iron complexes based on different ligand platforms are described. The complexes are subsequently studied for their... Show moreIn this dissertation, the synthesis and characterization of a series of iron complexes based on different ligand platforms are described. The complexes are subsequently studied for their activity in catalytic water oxidation with the help of a variety of electroanalytical techniques. The results show that the catalytic activity of structurally related iron complexes correlates strongly with the electronics of the iron centre. Another potentially very important aspect in the field of homogeneous electrocatalysis which has so far received only very little attention in published literature is the influence of the nature of the electrode material on the resulting electrochemistry. The results discussed in thesis show that interactions between the working electrode and the catalyst in solution can exhibit a strong influence on the resulting electrochemistry. Overall, the results of this work demonstrate that iron-based complexes can indeed be made to work as electrocatalysts for the water oxidation reaction. Furthermore, the results show that the electronic structure of the iron centre is a promising target for the design of new and improved catalysts. Finally, the results also highlight the importance of trying out different electrode materials as part of routine tests of new potential electrocatalysts. Show less
In this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less... Show moreIn this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less deleterious compounds, in order to cast light onto the mechanism of the reaction to achieve an efficient and selective system.The thesis is divided in two main parts, the reduction of nitrates(chapter 2) and the mechanistic study of CO2 conversion to different products such as ethanol(chapter 3), ethylene(chapters 4 and 5) and propylene carbonate (chapter 6). Show less
The research described in this thesis focused on the preparation of S/N functionalized carbene ligands and their transition metal complexes, and the exploration of their application as... Show moreThe research described in this thesis focused on the preparation of S/N functionalized carbene ligands and their transition metal complexes, and the exploration of their application as electrocatalysts for proton reduction. Show less
The PhD project was aimed to understand the role of the solvent in the hydrogen oxidation and evolution reactions on platinum and gold. This approach sheds light on the molecular origins... Show more The PhD project was aimed to understand the role of the solvent in the hydrogen oxidation and evolution reactions on platinum and gold. This approach sheds light on the molecular origins affecting the kinetics of the hydrogen evolution reaction, as a promising source of energy in the era of sustainable energy production and storage. Ultimately, this work demonstrates the importance of the solvent in the hydrogen electrocatalysis, specifically, water, by settling its role as a solvent, as a proton donor, and by preferential proton solvation, clarifying a long-existing debate regarding the pH dependence of the hydrogen evolution, and setting a path for future exploration of solvent-electrode interfaces for the tailoring of electrocatalytic reactions. Show less
In this study we focused on the simulation of the interaction of water and its dissociation products hydrogen, oxygen and OH with platinum surfaces that contain a periodic arrangement of single... Show moreIn this study we focused on the simulation of the interaction of water and its dissociation products hydrogen, oxygen and OH with platinum surfaces that contain a periodic arrangement of single-atom-high steps. We simulate these interactions using the framework of density functional theory and employ high-performance computing resources such as the Cartesius supercomputer of SURFsara. We find that the two possible types of step edges exhibit increased binding strengths compared to the flat parts of the interface. This binding strength is a key factor in the chemical reactivity of these surfaces. Furthermore, we investigate the structure of higher coverages of water molecules around the step edges, where we observe surprising changes, namely the appearance of four, five and seven-membered rings, compared to the six-membered rings that are usually observed on the flat surfaces. Our predictions for these structures are confirmed using high-resolution scanning tunneling microscopy data. Our results are among the first simulations of high-coverage water adsorption on regularly stepped platinum surfaces, which will help advance our understanding of solvation effects at the step edges, which are relevant for the fields of solvation science, electrochemistry and surface science. Show less
This thesis presents new insights into the reduction of carbon dioxide to methane and ethylene on copper electrodes. This electrochemical process has great potential for the storage of surplus... Show moreThis thesis presents new insights into the reduction of carbon dioxide to methane and ethylene on copper electrodes. This electrochemical process has great potential for the storage of surplus renewable electrical energy in the form of hydrocarbons. The research described in this thesis focuses on the molecular reaction mechanism, to identify key intermediates that determine the product selectivity. Show less
The primary goal of this thesis is to study the potential role of electrochemistry in finding new routes for sustainable chemicals from biomass in aqueous-phase solutions. In order to assess the... Show moreThe primary goal of this thesis is to study the potential role of electrochemistry in finding new routes for sustainable chemicals from biomass in aqueous-phase solutions. In order to assess the potential of electrochemistry in biomass conversion, we developed an online HPLC system by using a fraction collector with a micrometer-sized sampling tip placed close to the working electrode, with the collected sample fractions subsequently analyzed in an offline HPLC system. To demonstrate this method, we applied it to the poly-ols, i.e. glycerol (C3H8O3), electro-oxidation on Au and Pt electrodes at different pH conditions, visualizing the concentration changes of glycerol and its reaction products in correspondence with the current measured in voltammetry, which brought us a concept to co-generate hydrogen and valuable chemicals (i.e. glyceraldehyde, glyceric acid, dihydroxyacetone, formic acid) with high selectivity depending on the applied potential. In addition, we aimed at single-cell synthesis of sorbitol from cellulosic material by generating glucose as an intermediate species. This thesis has demonstrated the separate reactions of cellobiose hydrolysis to glucose by acid and hydroxyl radical on an anode and glucose hydrogenation to sorbitol on a cathode in an electrolysis cell. Show less
Nitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified... Show moreNitrate reduction on Sn-modified polycrystalline Pt has been investigated. NO is the main product at high Sn coverage, whereas N2O is dominant at low Sn coverage. The N2O reduction on Sn-modified Pt electrodes indicates electrochemical formation of N2 is related to pristine Pt sites. Moreover, homogeneous chemical reactions of intermediates products also contribute to N2O and N2 formation of in solution. The p-block metals have been studied: Cd, In and Sn show a promoting effect; Ga shows a limited enhancement; Tl shows a special promoting effect in sulfuric acid; Pb shows a weak formation of N2O. Density Functional Theory calculations show that Sn and In enhance nitrate adsorption compared with pristine Pt. Moreover, ammonia is found as the only product on Pt. After modification by Sn, hydroxylamine is specifically found with nitrite, which supports that nitrate reduction to nitrite is enhanced by Sn and Sn could steer the hydrogenation of NOads. However, solution pH is an important factor. On Pt, nitrate reduction is only observed in acidic solution. On Rh, a higher activity is observed in wide pH, which suggests a mechanism that HNO3 molecule is the active species. However, Rh additionally shows a special ability to reduce NO3- directly. Show less
This project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater... Show moreThis project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater remediation; electrochemistry strives to achieve selectivity to harmless products (N2). A multi-pronged approach has been followed, aimed at establishing the influence of several variables (electrocatalyst material, surface structure, pH and electrode potential) on the catalytic activity and the product distribution, which has been determined with in situ analytical techniques (mass spectrometry and infrared spectroscopy). The molecular underpinnings of nitrite reduction have thereby been unravelled for transition metals, showing that an optimal catalytic performance is achieved when metals intermediate affinities to reaction intermediates (Sabatier Principle). The all-important concept of structure sensitivity also applies to nitrite reduction at Pt electrodes, although only in alkaline media: a Pt(100) single-crystal is the sole Pt surface able to achieve the desired direct conversion of nitrite into 100% N2. Such selectivity is unparalleled for a simple monometallic surface and is an outstanding finding. Additionally, the nitrite-reducing performance of bio-inspired catalysts, (electroactive metalloporphyrins) was investigated. A further side-project of this PhD thesis has also been the electrochemical characterization of preferentially-oriented cuboid Pt nanoparticles synthesized with the innovative __cathodic corrosion__. Show less
We have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those... Show moreWe have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those sites. Under UHV conditions OH groups can be formed on Pt(111) by pre-covering the surface with O adatoms, causing water to dissociate. We have shown that on stepped platinum surfaces OHad might not be as readily formed as one would assume based on the energetics of OH adsorption alone. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on D/Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on D/Pt(553). Under electrochemical conditions we show that in spite of the similar looking cyclic voltammograms, the kinetics of underpotential deposited hydrogen are significantly different in acidic and alkaline media. In alkaline media the ad- and desorption process is slow, whereas it is very fast in acidic media. We have pointed out three discrepancies in the current interpretation of the blank cyclic voltammetry of stepped platinum surfaces and propose a co-adsorption model that accounts for these discrepancies. Show less
The main goal of the research presented in this thesis is the synthesis of suitable structural and functional models for the enzyme [NiFe] hydrogenase, which can reduce protons into dihydrogen. A... Show moreThe main goal of the research presented in this thesis is the synthesis of suitable structural and functional models for the enzyme [NiFe] hydrogenase, which can reduce protons into dihydrogen. A brief survey of the roles of all the known nickel containing enzymes in biological systems with a focus on the [NiFe] hydrogenases. Structure, function, physicochemical and catalytic properties of the [NiFe] hydrogenase itself and of the reported model complexes are presented. Many new Nickel, [NiFe], [NiRu] and [NiCu] complexes have been synthesized and studied in view of better catalysts for proton electroreduction into dihydrogen. Show less
Classically a nanowire with a length larger than its circumference is expected to be unstable due to Rayleigh instability that appears in specimens with large aspect ratio. In contrast we present... Show moreClassically a nanowire with a length larger than its circumference is expected to be unstable due to Rayleigh instability that appears in specimens with large aspect ratio. In contrast we present experimental evidence that metallic nanowires with thicknesses ranging from one atom to hundreds of atoms present two series of exceptionally stable diameters, well determined and reproducible. The two series of stable diameters can be described in terms of shell closure effects. For low diameters the stability is given by the confinement of the electronic orbits in the nanowire cross-section, which is an electronic shell effect. Thicker nanowires are stable for densely packed structures, related to minima in the surface energy, which we refer to as atomic shell effect. A significant part of this thesis is dedicated to the study of shell effects for different types of metals: the monovalent noble metals, and multivalent Al and Mg. Additionally we investigate the stability from a mechanical point of view by measuring the stiffness of atomic contacts. The last chapter is dedicated to electrochemical methods of nanowire fabrication and we explore possible ways of enhancing the nanowire stability. Show less
