Fossil fuels, which are the main energy sources of the current world, are running low and alternative ways of generating and storing different types of energies are becoming daunting missions. Renewable energy is very attractive because the source of the energy is often free and also environmentally friendly. The key issue to utilise the renewable energies in sustainable manner is how effectively store the energies and provide them on demand. Therefore, the significance of the energy storage devices has been widely recognised in recent time. Electrochemical capacitors (ECs), which are also commonly known as supercapacitors, are a type of the energy storage devices and the ECs are widely used as a back-up power boosting device to the batteries. Due to EC's low energy characteristics (typically, lower than 5 Wh/kg), their applications are limited. Therefore, main aim of this study is to enhance the energy characteristics of the ECs. In particular, aqueous ECs were examined due to a number of advantages offered by the water-based system. It was found that neutral aqueous electrolytes can expand the operating voltage close to 2 V (aqueous ECs commonly operate within 1 V) with advanced designs and hence result in remarkably higher energy. Moreover, the optimum condition of the neutral aqueous electrolytes was investigated by examining the effect of ion size, concentration and temperature. One of the main disadvantages of using the aqueous electrolytes in low temperatures was successfully resolved by using concentrated electrolytes (freezing point depressed up to -20°C). Mn02 with carbon materials were also used to construct asymmetrical ECs. The highest specific energy (Wh/kg) of the neutral aqueous ECs was achieved at 20 Wh/kg using unequal electrode design. This result is very much comparable to the Pb-acid battery. Based on the obtained data, larger scale (thicker and bigger electrode films) of the prototype ECs were constructed and their results correspond well with the results obtained from the smaller ECs. The data of the neutral aqueous ECs, which is contained in this thesis, suggest that the water-based ECs have a remarkable market potential.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:659295 |
| Date | January 2014 |
| Creators | Chae, Jung Hoon |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/30936/ |
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