Carbon nanotubes8/16/2023 ![]() ![]() And with equally impressive electrical and thermal properties these hollow tubes of carbon, just one atom thick, are proving to be one of the most versatile materials ever discovered. The results indicated that the pyridinic N sites exhibited superior ORR reactivity, followed by the quaternary N (graphitic N), and the pyrrolic N showed the worst ORR performance amongst these N sites.With a strength-to-weight ratio 117 times greater than steel, carbon nanotubes are the strongest and stiffest material known to man. Both aryne cycloaddition and aryl diazonium functionalization methods were adopted to functionalize with different types of N sites. In Chapter 6, the the highly oriented pyrolitic graphite (HOPG), which highlights on planar surface and eliminates trace iron and defects, were used as carbon substrate for the conceptual study. The ORR performance of each type of N sites were compared based on the N-functionalized CNTs. The results indicated that the precursors were successfully functionalized, and the ORR performance was maintained for the highly functionalized samples, revealing that the proposed idea was achieved on controlling the polymerisation of intermediates. To minimise the polymerization of molecules, in Chapter 5, N-heterocyclic amines were utilised as precursors to functionalize the CNTs via aryl diazonium reaction by creating a single C-C bond between the molecules and CNTs. The investigation on the structure-performance relationship revealed that the reactive pyridine intermediates were likely to polymerise during the functionalisation process, which substantially reduced the ORR performance. Different level of N sites on the CNTs were achieved by manupulating the stoichiometry of reagents. In Chapter 4, the 3,4-pyridyne precursor was used to functionalise multi-walled carbon nanotubes (MWCNT) via cycloaddition reaction, where two C-C sp3 bonds were created between the external pyridine molecule and the CNTs. The research backgrounds and fundamentals were introduced and discussed in Chapter 1, followed by the literature review on recent arylation strategies with carbon materials in Chapter 2. In this thesis, the aim was to develop novel synthetic methods to precisely manuipulate the type of N structures and the level of N sites in NCMs, as well as understand the ORR mechanisms on different types of N sites. Carbon nanomaterials have been widely used as the substrate for electrocatalyst, and the well-defined sp2 structures of the graphitic layer allows direct covalent functionalization of precursors. The true active N site(s) in NCMs for ORR has been controversial over the past decade, which profoundly hindered the implementation of NCMs. The preparation of NCMs generally undergoes a high-temperature process and produces three types of N sites (i.e., pyridinic, pyrrolic, and graphitic) in the carbon substrate. Metal-free nitrogen-doped carbon materials (NCMs) feature excellent ORR performance, low-cost, and sustainable resources as an ideal alternative to the Pt/C catalyst. The sluggish kinetics in oxygen reduction reaction (ORR) is one of the key challenges in the hydrogen fuel cells (HFCs). ![]()
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