The development of highly efficient, low cost oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) electrocatalysts has been a major focus for producing effective electrochemical devices for energy conversion and storage, such as fuel cells, electrolysers and air-batteries. This thesis addresses the synthesis, structure and electrocatalytic performance of graphene and molybdenum disulphide based nanomaterials for the ORR and HER. The work presented in this thesis focuses on three main thrusts: (i) the synthesis of few layer nanosized graphene for the electrocatalysis of ORR, (ii) the enhancement of ORR electrocatalytic properties of graphene through the incorporation of nitrogen, (iii) the development of MoSL electrocatalysts with enhanced HER performance. Few layer graphene nanosheets were synthesised through a novel ionic liquid grinding method followed by centrifugation as a size selection technique. The techniques produces high quality low oxygen (<2.5+0.2 At. %) nanosheets with low defect formation, due to the natural lubricating effect of the RTIL. The electrocatalytic performance was measured for the ORR on a range of sheet size and thicknesses. As expected, the highest ORR catalytic performance recorded originated from the sediment containing the thinnest and smallest lateral dimensions of all graphene samples (10K), with an onset potential of -0.13 V (vs Ag/AgCl), as measured using LSV. Similarly, the ionic liquid exfoliation technique was applied to MoSL, to produce few layered nanosheets for the catalytic enhancement of the HER. A highly active HER response was observed with exceptional durability for the smallest and thinnest nanosheets obtained. Ground sediment from a low purity graphite (99.0 %) was pyrolised at 700 [degree]C in a 1:5 mixing ratio with melamine (NGP). As confirmed by various topographical imaging techniques, a plethora of nanotube structures were grown as a direct result of the natural impurities imbedded in the starting graphite material. The ORR catalytic response observed was one of the highest performances observed when compared with literature, with an onset potential of -0.03 V and 4 e· transfer pathway. In addition, small sized NrGO synthesised through a hydrothermal method displayed a close to 4 e- ORR performance. The catalytic response showed a highly stable ORR performance when subjected to methanol poisoning.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:694214 |
| Date | January 2016 |
| Creators | Benson, John A. |
| Publisher | Ulster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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