City Research Online

Abstract

The energy crisis of the seventies has triggered off tremendous interest towards the research and development of alternative energy sources for the future. The use of hydrogen as the ultimate secondary fuel in the future would be economically feasible if the advancement in water electrolysis technology by using off-peak energy derived from either nuclear or solar power, approaches 100% energy efficiency. The present investigation is directed towards this goal, in the line of searching for new, inexpensive electrocatalysts, and looking at the suitability of the teflon-bonded porous electrode structure, being used for the hydrogen evolution reaction in alkaline media.

Evaluation of nickel sulphide materials lead to the synthesizing and examination of cobalt-nickel-sulphur compounds from cobalt-nickel oxide of composition NiCo2 04. The kinetics of the sulphiding process were investigated. By studying the preparation parameters carefully, cobalt-nickel-sulphur compounds prepared were best represented by the empirical formula of NiCo 20 xSy + Sz, where x+y <4, and y>> z 20. The best iR corrected electrochemical activity for the hydrogen evolution reaction was 1 A/cm2, at a potential of -170 mV vs D.H.E., in 5N KOH, at 70°C. The percentage of sulphur content in the cobalt-nickel-sulphur compounds play a major role in the determination of hydrogen evolution activity. The ability of cobalt-nickel-sulphur compounds to function efficiently as hydrogen cathode electrocatalysts, may be attributed to the defect structure of the catalysts, which show anion deficiency and thus create electrons at the conduction band to facilitate the hydrogen evolution process. Powder crystallographic measurements of all cobalt-nickel-sulphur compounds in this work showed predominantly spinel-type crystal structure, but with distortions as a result of mixed phases contamination.

The teflon-bonded porous electrode structure was found to be more active for the hydrogen evolution reaction as compared to the 'dipping' porous electrode structure. The disintegration of the 'dipping' porous electrodes was sometimes observed either before or during the hydrogen evolution process. This may be attributed to the hydrogen embrittlement of the electrode supports during the sulphiding process.

Finally, the electrode kinetic parameters for the hydrogen evolution reaction were determined at temperatures of, 25°C, 40°C and 70°C on cobalt-nickel-sulphur compound and a slow electrochemical desorption step is therefore suggested.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > Q Science (General) Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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