Preparation, characterization and application of boron-doped diamond powders: Application as an electrocatalyst support and a stationary phase for HPLC.

摘要

In this dissertation the growth, physical, and electrochemical properties of boron-doped microcrystalline (BMD) and ultrananocrystalline (B-UNCD) diamond coated powders was studied. Targeted uses of these electrically conducting diamond powders are as an electrocatalyst support for the polymer electrolyte membrane fuel cell and as a stationary phase for HPLC.;B-UNCD thin films on Si were prepared with varying B2H 6 (0-50 ppm) and CH4 concentration (0.5 to 3% v/v) to investigate the dependence of the B-UNCD morphology, microstructure and phase purity on the source gas composition. Ultrananocrystalline diamond was only formed at the 1% CH4 level. Boron concentration within the films was linearly dependent on the boron concentration in the gas phase as determined by nuclear reaction analysis. There were no significant microstructural changes among the films grown between 0-50 ppm B2H6 in the gas phase.;B-UNCD formation on diamond powders (500, 100, and 3-6 nm diam.) and carbon black powders (glassy carbon and Ketjen black) was evaluated using electron microscopy, Raman spectroscopy, EELS, and XRD. The B-UNCD formed on the powder is the predominant microstructural phase deposited, with non-diamond sp2 carbon phases interspersed.;Electrochemical and in situ Raman spectroscopic measurements were made with BMD powders before, during and after potentiostatic polarization in aqueous acid. Electrodes were prepared by casting a powder slurry on a glass slide with Nafion serving as the binder. The potentiostatic polarization was performed in either 0.1 M HCIO4 or 0.1 M H2SO 4 at 1.0, 1.2 and 1.4 V vs. Ag/AgCl. The polarizations were conducted at two temperatures: room temperature and 80 °C. Similar studies were conducted using B-UNCD powders packed into a pipette electrode with no binder. Comparison studies were also performed on Vulcan XC-72 and several microstructurally-varied sp2 carbon powders; graphite, glassy carbon and acetylene black. It was found that the boron-doped diamond powders are dimensionally stable and corrosion resistant, while the carbon black powders underwent more severe microstructural degradation.;The performance of boron-doped diamond powder (BDDP) as a stationary phase in electrochemically modulated liquid chromatography was investigated and its stability as a packing relative to porous graphitic carbon (PGC) was compared. The results show that BDDP is stable over a wide range of Eappi values (i.e. -1.2 to +1.2 V vs. Ag/AgCl). The data also reveal that electrostatics play a key role in the adsorption of the aromatic sulfonates on the BDDP stationary phase, and that these analytes are more weakly retained in comparison to the PGC support.