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|Title:||Fabrication of carbon-based nanomaterials for energy conversion|
|School/Discipline:||School of Chemical Engineering|
|Abstract:||Nowadays, energy is one of the most important challenges facing mankind due to its supply and demand issues and global warming. Replacing unsustainable energy sources such as fossil fuels is among the most critical issues in the 21st century. Among different solutions for the energy challenges, electrochemistry which studies the conversion between electricity and energy stored in chemical bonds can be used to solve these issues without any significant impact to the environment. One of the energy conversion limitations in electrochemical processes is extra energy requirements to overcome the high activation barriers. To overcome this problem, electrocatalysts are always utilized to improve electrode efficiency in order to decrease activation energy and increase energy conversion. Electrocatalysts should be lowcost, durable, efficient and sustainable. One of the main categories of electrocatalysts in energy conversion reactions is precious metal- based materials which have high performance. However, they cannot be applied at large scales due to their high cost, scarcity, limited supply and weak durability. Thus, other alternative electrocatalysts based on lower cost material such as non-precious metal or metal free catalysts have been widely developed. Carbon-based materials are one of the most important materials which have been playing a significant role in the development of energy conversion and storage devices because of their abundance, low cost, stability, easy accessibility, good recycling, and relatively environmentally friendly characteristics with high durability, especially in alkaline medium. This thesis aims to design and fabricate a series of advanced electrocatalysts for the different range of electrochemical reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) which are principals of various types of energy conversion devices. The first part of the thesis focuses on the development of metal-free nitrogen-doped mesoporous carbon spheres prepared via soft-templating procedure by tuning different nitrogen precursor contents and carbonization temperature. The synthesized electrocatalyst showed a favourable catalytic activity in ORR with high kinetic current and positive onset potential due to its high surface area, high pore volume, narrow mesopore size distribution, high conductivity and high nitrogen content. In the second part, carbon-based composites co-doped with nitrogen and trace amount of metallic cobalt have been developed as electrocatalysts for water splitting system at low overpotential and high current density. An excellent electrochemical activity of newly developed electrocatalyst originates from its graphitic nanostructure and highly active Co-Nx sites. Based on the spectroscopic and electrochemical investigations the newly identified Co- Nx sites in the carbon framework are responsible for the high electrocatalytic activity of the Co, N-doped carbon. The third research project is to utilize the physical synthesis technique to ensure high control and tunability of morphology, structure and composition of multi-component materials. In this context, pulsed laser deposition (PLD) is particularly versatile in the tuning of properties of deposited materials which is based on ablating a target material by laser pulses and has been applied to develop new carbon-based thin films. Thus, cobalt oxide nanoparticles deposited on porous nitrogen -doped carbon films were successfully developed via a two-step pulsed laser deposition technique. The synthesised material behaves as an efficient OER electrocatalyst with superior activity in alkaline electrolyte. The excellent catalytic activity of prepared electrodes could be attributed to the surrounding N-carbon framework, and it was found that a higher ratio of Co2+/Co3+ yields better catalytic activity towards the OER. Transport of reactants and products involved in electrochemical reactions was also facilitated by the porous structure of material. Additionally, the carbon framework, comprising carbons adjacent to cobalt (oxide) nanoparticles, increases catalytic sites and prevents the aggregation or dissolution of nanoparticles. The last part of the thesis aims to design an efficient and stable bifunctional electrocatalyst for both HER and OER in the same electrolyte for overall water electrolysis. Thus a novel type of robust binary Ni-Co nanoparticles coated on porous N-carbon thin film with low overpotential has been reported. The efficient OER activity might be contributed to the available metal oxide nanoparticles with effective electronic structure configuration, enhanced mass/charge transport capability. At the same time, the porous nitrogen doped carbon incorporated with cobalt and nickel species might serve as an excellent HER catalyst. As a result, the newly developed electrocatalysts manifest high current densities and strong electrochemical stability in overall water splitting, outperforming most of the previously reported non-precious metal-based counterparts.|
|Dissertation Note:||Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2017|
|Provenance:||This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals|
|Appears in Collections:||Research Theses|
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