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
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
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
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
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
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
The thesis contains work on the catalytic mechanism, and then especially on the reversibility of the reaction and the order of substrate addition and reduction of the catalytically active type-2... Show moreThe thesis contains work on the catalytic mechanism, and then especially on the reversibility of the reaction and the order of substrate addition and reduction of the catalytically active type-2 copper site. Furthermore, protein engineering of the type-1 copper site is reported and a study into the reorganizational energy of this site. Show less
