Photochemical systems for the splitting of water into hydrogen and oxygen represent an attractive route for the conversion of solar energy into a chemical fuel. However, the success of such systems depends on the identification of suitable redox catalysts for the oxidation and reduction processes. While colloidal platinum has proved to be an efficient catalyst for the reduction of water, the development of stable and effective catalysts for water oxidation has been less successful. The work described in this thesis involves the study of ruthenium dioxide hydrate (RuO<SUB>2</SUB>.xH<SUB>2</SUB>)O as a heterogeneous catalyst for the oxidation of water to oxygen. Although this material has already been widely used as an oxygen catalyst, there have been many doubts as to its ability to act in this capacity. In Chapter Three an attempt is made to resolve this controversy via an investigation of the stability and catalytic activity of RuO<SUB>2</SUB>.xH<SUB>2</SUB>O when exposed to various oxidising agents. The results indicate that the catalytic activity and corrosion stability of an RuO<SUB>2</SUB>.xH<SUB>2</SUB>O sample is related to its degree of hydration. In Chapter Four an investigation is described into the effect of heat-treatment of RuO<SUB>2</SUB>.xH<SUB>2</SUB>O at different temperatures on its physical and chemical properties. From these results it appears that any sample of RuO<SUB>2</SUB>xH<SUB>2</SUB>O may be transformed into a stable, reproducible oxygen catalyst by simply heat-treating it at 140-150<SUP>o</SUP>C in air for <i>ca</i>. 5 hours. The latter conditions represent an optimum for catalytic activity where anodic corrosion is absent. This 'thermally-activated' RuO<SUB>2</SUB>.xH<SUB>2</SUB>O is shown to compare favourably with alternative oxygen catalysts. Chapters Five and Six involve a kinetic study of the RuO<SUB>2</SUB>.xH<SUB>2</SUB>O-catalysed oxidation of water by Ce(IV) ions in an attempt to elucidate the mechanism of catalysis of the oxide powder. The study is based on an electrochemical model in which the RuO<SUB>2</SUB>.xH<SUB>2</SUB>O particles are considered as microelectrodes. The initial charging of the RuO<SUB>2</SUB>.xH<SUB>2</SUB>O prior to water oxidation is discussed in Chapter Five and in Chapter Six the effect of an increase in the redox potential of the Ce<SUP>4+</SUP>/Ce<SUP>3+</SUP> couple by changing the acid medium is investigated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637056 |
| Date | January 1988 |
| Creators | Giddings, S. L. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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