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New boron doped diamond materials for electrochemical applications
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Wood, Georgia F. (2021) New boron doped diamond materials for electrochemical applications. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3781804~S15
Abstract
In this thesis, novel fabrication methods of conductive sp3 bonded boron doped diamond (BDD) materials are established. The intentional integration of sp2 bonded carbon is also examined, where the contrasting physical and chemical properties when compared to sp3 bonded carbon can be exploited. BDD electrodes are desirable for many applications due to their superior material properties including wide anodic window in water and excellent chemical and electrochemical stability. High pressure high temperature (HPHT) synthesis of crystallographically well-defined BDD microparticles (MPs), suitable for electrochemical applications and using the lowest P and T (5.5 GPa and 1200 °C) growth conditions to date, is reported. A HPHT compaction process is used to create freestanding sub microscopic porous electrodes from the BDD MPs, which boast the electrochemical and mechanical robustness properties of BDD but with the additional benefits of a large, electrochemically accessible, surface area. These HPHT BDD electrodes also offer an alternative to traditional chemical vapour deposition (CVD) grown BDD, with potential for low cost scalability. Moving to the nanoparticle (NP) size regime is also investigated, by mechanically grinding CVD BDD using a planetary ball mill. BDD NPs are desirable for applications such as proton exchange membrane fuel cells (PEMFCs), where traditional sp2 bonded carbon catalyst supports suffer from short lifetimes due to corrosion.
The MP compacted electrodes can be laser micromachined into perforated (slotted) geometries and in this thesis, are then utilised for electrochemical ozone production (EOP) from water, an attractive, green technology for disinfection. The HPHT BDD electrodes are shown to exhibit high EOP, producing 2.23 ± 0.07 mg L-1 of ozone per ampere of current, at consistent levels for a continuous 20 hr period with no drop off in performance. BDD EOP electrodes are fabricated with varying percentages of sp2 bonded carbon (from 5% to 80%), revealing the importance of sp2 carbon presence for EOP. The sp2 carbon is introduced during laser micromachining, where the BDD is converted during oxidative acidic treatment to a ~5 nm thick layer of robust sp2 bonded carbon, termed diamond stabilised non-diamond carbon (DSC). The improved EOP is thought to be due to stronger hydroxyl (·OH) and oxygen (·O) radical absorption which ultimately equals increased ozone output and current efficiency. The DSC is shown to be stable over numerous oxidative acid treatments and believed to be stable over 20 hr continuous EOP, as no reduction in performance is observed. Finally, two novel fabrication routes are developed to produce electron beam transparent BDD substrates for combined electrochemical (EC)-transmission electron microscopy (TEM). The first involves ion milling whilst the second involves electrochemically induced lift off of a thin BDD membrane.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Boron, Diamonds, Electrochemical analysis, Doped semiconductors | ||||
Official Date: | October 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Macpherson, Julie V. | ||||
Sponsors: | Engineering and Physical Sciences Research Council ; University of Warwick | ||||
Extent: | xx, 179 leaves : illustrations, charts, photographs | ||||
Language: | eng |
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