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Title: Shining light on electrode interfaces
Author: Galloway, T. A.
ISNI:       0000 0004 7428 4245
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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The metal-oxygen battery is the pinnacle of beyond Li-ion battery technologies, providing a very high theoretical specific energy relative to current battery chemistries. However, the practical use of alkali metals (Li and Na) in the presence of oxygen species and carbon cathodes provides substantial problems in the development of this technology. The highly nucleophilic and reactive nature of the reduced alkali-oxygen species causes degradation of the electrolyte and cathode. In order to overcome these factors, the fundamental reaction mechanism taking place at the solid/electrolyte interface need to be understood. In this thesis, a range of electrochemical and spectroscopic techniques have been used to help elucidate the reaction pathways and products. Initial studies have been conducted using shell isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) to allow surface enhanced Raman studies on previously inaccessible electrode materials. The use of SHINERS utilised the localised surface plasmon from the gold nanoparticles without any additional effect from the particle surface, due to the Raman inactive silica shell. This allowed the vibrational modes of nearby molecules adsorbed on the surface to be enhanced. A comprehensive characterisation and analysis of SHINERS, as well as their functionality on a range of different electrode morphologies has been presented. SHINERS have been used to compare the oxygen reduction reactions (ORR) with and without the presence of lithium on a variety of polycrystalline electrodes. The behaviour of superoxide (O2 .- ) without the presence of lithium was shown to be highly dependent on the electrode surface. The ORR in the presence of lithium was demonstrated to be both surface and solvent dependent on a range of carbon electrodes. SHINERS were also used to study more practical battery electrodes, with the detection of lithium oxides and side products on the electrode surface after discharge and charge. The use of single crystal electrode surfaces were also studied, in order to provide an ideal surface to understand the reaction mechanisms. The effect of moving from an aqueous to a non-aqueous electrolyte on a gold (111) surface was studied using voltammetry and SHINERS. The inhibition of the electrode surface with trace amounts of MeCN was detected. The degradation of MeCN was also observed with trace amounts of water. Finally the behaviour of the sodium-oxygen system was studied on the three low index basal planes of platinum (111), (110) and (100). The electrochemical behaviour was shown to be facet dependent, with the addition of a supporting salt also affecting the reaction mechanism taking place.
Supervisor: Hardwick, L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral