Towards the nanoscale : electrocatalysts and their supports
Patten, Hollie V. (2011) Towards the nanoscale : electrocatalysts and their supports. PhD thesis, University of Warwick.
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Electrocatalysts and their support materials used for fuel cell (FC) technology remain at the forefront of research in this field. Typically FC electrocatalysts are comprised of Pt nanoparticles (NPs) supported by carbon. Improvement of both the efficiency and the durability of the materials is required to increase the overall FC performance. To achieve these goals requires a fundamental understanding of electrocatalysis at composite materials and the exploration of alternative materials. These aspects are explored in this thesis. Highly oriented pyrolytic graphite (HOPG) and poly-(3,4-ethylenedioxythiophene) PEDOT-coated HOPG were used as support materials for the electrodeposition of Pt NPs. The NPs were characterised using atomic force microscopy (AFM) which showed that by applying an ultra-thin (ca. 2 nm) of PEDOT, a conducting polymer (CP), onto HOPG, there was less tendency for NP aggregation, with no preferential deposition, i.e. at step edges, and also smaller particles were formed. PEDOT-coated HOPG as the support material for Pt NPs showed a significant enhancement of electroactivity for methanol oxidation, by an order of magnitude, compared with similarly prepared NPs on native HOPG. An alternative support material; explored in this thesis, was polycrystalline boron doped diamond (pBDD), owing to its stability in harsh environments, analogous to FCs. During growth, boron uptake varies across the exposed surface of pBDD, leading to a heterogeneous substrate with typical grain sizes of 5-40 μm. Two new scanned probed techniques; intermittent contact - scanning electrochemical microscopy (IC-SECM) and scanning electrochemical cell microscopy (SECCM) were employed to investigate the impact of this heterogeneity on the local electrochemical properties. Maps using IC-SECM revelaed that the entire surface was active, but that areas with higher boron concentration were more electroactive. Grain boundaries showed no enhanced activity. The maps were sucessfully correlated to the boron dopant density using micro-Raman mapping and field emission scanning electron microscopy (FE-SEM). Similarly, SECCM maps also proved that the entire surface is electrochemically active with the heterogeneities relating to boron content. For data obtained by both techniques finite element simulations (FEM) were employed to extract values for the standard rate constant, k0. With knowledge of the fundamental properties of pBDD, the successful fabrication of a pBDD rotating disk electrode (RDE) is reported which is fully characterised. By functionalisation of pBDD with Pt NPs, the oxygen reduction reaction (ORR) has been studied and compared with a bulk Pt RDE. These preliminary studies show potential for gaining insight into the kinetics of the ORR.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QD Chemistry|
|Library of Congress Subject Headings (LCSH):||Electrocatalysis, Fuel cells, Nanoparticles, Electroplating|
|Institution:||University of Warwick|
|Theses Department:||Department of Chemistry|
|Supervisor(s)/Advisor:||Unwin, Patrick R. ; Macpherson, Julie V.|
|Sponsors:||National Physical Laboratory (Great Britain)|
|Extent:||xvii, 160 leaves : ill., charts|
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