Developing low cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts that perform with high efficiency is desirable for the commercial success of energy conversion devices, such as fuel cells and metal-air batteries. In this thesis, electrochemically reduced graphene oxide (ErGO) and Mn304 nanoflakes anchored on nitrogen doped reduced graphene oxide (NrGO) sheets synthesised by electrodeposition method were developed as ORR catalysts. CUC0204 nanoparticles were integrated with NrGO sheets through solvothermal method as a potential OER catalyst. A partially reduced graphene oxide electrocatalyst synthesised by electrochemical reduction of graphene oxide exhibited significantly enhanced catalytic activity towards the ORR in alkaline solutions compared to the starting GO. The resultant ErGO electrode also showed an enhanced capacitance and an ORR onset potential similar to that of NrGO electrode, produced by a solvothermal process. However, the ErGO exhibited considerably lower electron transfer numbers, indicating that although both catalysts operate under combined 4e- and 2e- ORR processes, ErGO followed a more predominant 2e- pathway. The ORR process in ErGO has been linked to the presence of quinone functional groups, which in turn favoured the 2e- ORR pathway. Also in this work, a three dimensional Mn304 hierarchical network was grown on NrGO by a facile and controllable electrodeposition process, and its electrocatalytic performance for ORR was assessed. The directly electrodeposited MnO. on the glassy carbon electrode (GCE) exhibited little electrocatalytic activity, whereas the integrated Mn304/NrGO catalyst was more ORR active than the NrGO. The resulting electrode architecture exhibited an "apparent" 4e-oxygen reduction pathway involving a dual site reduction mechanism due to a synergetic effect between Mn304 and NrGO. In addition, the 3D Mn304/NrGO hierarchical al'chitectur~ exhibited improved durability and methanol tolerance, far exceeding that of commercial ptlC. A composite material consisting of CUC020 4 nanoparticles anchored on NrGO sheets (CuCo204/NrGO) was prepared by a solvothermal method as a highly efficient OER electrocatalyst in both alkaline and neutral solutions. The CuCo204/NrGO exhibited high OER performance when compared to the other control materials, as well as good stability under strong alkaline condition. The enhanced OER performance of CuCo204/NrGO can be related to: (i) a reduction in the size of the CUC0204 nanoparticles as measured by the TEM, (ii) an enhancement of electrochemically active surface area (ECSA), (iii) a replacement of the least OER active C02+ ions with Cu2+ ions as confirmed by XPS and (iv) a synergetic effect between CuCo204 nanoparticles and NrGO sheets.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:673823 |
| Date | January 2015 |
| Creators | Bikkarolla, Santosh Kumar |
| Publisher | Ulster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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