Magnetic field effects on electrochemical systems, lanthanide electrochemistry, thin layer sonoelectrochemistry and models for polymer film characterization

Nadeesha Pavithri Wickramasri Rathuwadu

doi:10.25820/etd.007198

The studies are focused on four main areas, electroanalytical characterization of polymers, applications of lanthanide electrochemistry, magnetic field effects on electrochemical systems, and thin layer sonoelectrochemistry. Polymers are important in different fields such as energy storage, energy generation, and pharmaceuticals. Two different types of polymers, a cation exchange polymer Nafion^{®} and compressible polymers were studied. Nafion is used in numerous applications because of unique properties. Despite extensive use, the activity of Nafion and local charge compensation mechanism during a voltammetric perturbation are long standing questions. Observed high currents during voltammetric perturbation require effective local charge compensation mechanisms. A model is developed for the charge compensation mechanism. Nafion properties, like charge compensation and conductivity, are set by activity in Nafion. As the first step to understand the local charge compensation, an activity model of Nafion is developed. Nafion behavior can change when multiple redox probes are present. If more than one redox probe is present, cross exchange reactions should be considered as part of the charge compensation and effective diffusion by electron hopping. The compressible polymers are an interesting class of polymers with various commercial applications in pharmaceuticals industry. However, compressible polymer characterization involves complicated procedures that typically involve high pressures. Electrochemical characterization of compressible polymers may provide a simpler method but the methodology is not yet developed. Cyclic voltammetry and rotating disk experiments were undertaken in support of developing diagnostics and a model for compressible polymers characterized electrochemically. Magnetic field effects (MFE) are introduced in electrochemical systems to increase efficiencies. The most common focus is to increase the mass transport and achieve more efficient systems. Here, magnetoelectrocatalysis to increase heterogeneous electron transfer rates is the focus. Magnetic microparticles are incorporated on the electrode surface to increase the spin transfer processes of slow heterogeneous processes. MFE on three electrochemical systems and related reactions of palladium hydride storage, lithium and lithium ion battery, and hydrogen evolution reaction were studied. Hydrogen is considered an excellent alternative energy source. However, lack of efficient storage methods is a problem that prevent H₂ from being a commercial energy source. The solid phase storage as metal (palladium) hydrides is a better option compared to liquid and gaseous phase storage, but hydride storage is kinetically limited. Magnetic fields increased the efficiency of hydride storage. There are great advantages of lithium and lithium ion batteries. However, despite the great advantages, demand for better options for energy generation and storage increases and research is done to further efficiency. In this study, a novel approach for lithium ion battery research is undertaken to increase the efficiency of lithium and lithium ion batteries by incorporating micromagnets. Magnetic fields increased the efficiency of a principle reaction in lithium and lithium ion batteries. Hydrogen evolution reaction (HER) and its product H₂ are important in numerous energy generation and storage processes and industrial processes. H₂ is produced by steam reformation of natural gases (methane), an expensive process that consume the nonrenewable energy sources. Other methods of H₂ production include electrolysis and coal gasification. To have an electrochemical method to produce H₂, inexpensive electrode materials with low overpotential are needed. Incorporation of magnetic fields increased the efficiency of poorly electrocatalytic electrodes. There are many applications of lanthanides in advanced technologies such as lasers, permanent magnets, medical imaging, and catalysts. Lanthanides are produced as decay products in nuclear reactors. Therefore, it is important to have efficient lanthanide analysis methods. Existing lanthanide detection and separation methods are expensive, sophisticated, and notably inefficient. The motivation is to develop a simple electrochemical method for lanthanide analysis. A novel method was developed to perform lanthanide electrochemistry and applications of the novel method were tested on electrocatalysis and lanthanide separation. Electrocatalysis of carbon dioxide reduction and electrochemistry of a sequence of single carbon compounds were studied. CO₂ is a prevalent green house gas that contributes to global warming. Methods to convert CO₂ to value added compounds include CO₂ reduction. Electrochemical reduction of CO₂ is one means. The sequence of single carbon species maps the thermodynamic advantages of organic electrochemical fuels and identifies the dominant kinetic limitations of C-1 electrochemistry exploitation in practical, low temperature electrochemical energy systems. Most of these reaction are kinetically limited. Electrochemistry of formic acid, acetaldehyde, methanol, and carbon monoxide were considered. These reactions were mediated by lanthanide complexes. Also, preliminary evaluation of several lanthanide mixtures was undertaken to assess possible lanthanide separation methodologies. Sonoelectrochemistry has significant impact on electrochemical processes. Sound waves impact chemical process by a physical phenomena, cavitation rather than by chemical means. Cavitation cleans and activates electrode surfaces and enhance mass transport. In bulk sonoelectrochemistry, high intensity sound waves are used and extensive turbulence and cavitation are observed. Effects are due to enhanced mass transport. Effects on heterogeneous rates cannot be observed in the turbulent matrix of cavitation. The objective of thin layer sonoelectrochemistry is to develop a system that supply just enough energy to enhance heterogeneous rates without excessive turbulence and cavitation. In thin layer sonoelectrochemical cells the sound energy is harvested more efficiently compared to the bulk systems. The fundamental mechanism of thin layer sonoelectrochemistry is yet to be fully understood. To support understanding of the fundamental processes, investigations of dependence on fundamental parameters are undertaken to identify modes of enhancement in thin layer sonoelectrochemistry and to understand fundamental mechanisms. Here, results are reported for solvent dependence. Solvent is a crucial factor as it participate in sound wave propagation. Density affect the speed of propagation and viscosity effect the attenuation of the energy. Solvent with low density and viscosity are matrices better able to support energy transmission in thin layer sonoelectrochemical cells. The effect of thin layer sonoelectrochemistry on palladium hydride storage was also studied. Increased efficiency for hydride storage was observed on sonication.

Magnetic field effects on electrochemical systems, lanthanide electrochemistry, thin layer sonoelectrochemistry and models for polymer film characterization

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