The Physicochemical and Electrochemical Properties of 100 and 500 nm Diameter Diamond Powders Coated with Boron-Doped Nanocrystalline Diamond

Abstract

There is a need for advanced, corrosion-resistant electrocatalyst support materials for use in fuel cells. To this end, electrically conducting diamond powder was prepared by depositing a layer of boron-doped nanocrystalline diamond on 100 and 500 nm diam diamond powders. The doped layer was deposited by microwave plasma-assisted chemical vapor deposition using an Ar-rich CH 4 /H 2 /Ar/B 2 H 6 source gas mixture. After coating, the 100 nm doped diamond powder had a specific surface area of 27 m 2 /g and an electrical conductivity of 0.41 S/cm. The 500 nm doped diamond powder had a specific surface area of 8 m 2 /g and an electrical conductivity of 0.59 S/cm after coating. The specific surface area of both powders decreased by ca. 50% after diamond coating due mainly to particle-particle fusion. The electrical measurements provided conclusive evidence for a doped diamond overlayer as the uncoated powders possessed no electrical conductivity. Furthermore, the fact that the electrical properties were unaltered by acid washing confirmed that the conductivity arises from the doped diamond overlayer and not any adventitious sp 2 carbon impurity on the particle surface, which is removed by such chemical treatment. Scanning electron microscopy images and Raman spectroscopy yielded further evidence in support of a nanocrystalline diamond overlayer. Both powders exhibited electrochemical responses for Fe͑CN͒ 6 3−/4− , Ir͑Cl͒ 6 −2/−3 , and Fe +2/+3 that were comparable to typical responses seen for high-quality, boron-doped nanocrystalline diamond thin-film electrodes. The electrochemical behavior of the powders was assessed using a pipette electrode that housed the packed powder with no binder. The 100 nm doped diamond powder electrodes were more plagued by ohmic resistance effects than were the 500 nm powder electrodes because of reduced particle contact. Importantly, it was found that the doped diamond powder electrodes are dimensionally stable and corrosion-resistant during anodic polarization at 1.4 V vs Ag/AgCl ͑1 h͒ in 0.5 M H 2 SO 4 at 80°C. In contrast, glassy carbon powder polarized under identical conditions underwent significant microstructural degradation and corrosion.

Diamond Nanostructures and Nanoparticles: Electrochemical Properties and Applications

“…Both powders had increased conductivities. Well-defined electrochemical responses were obtained on these powders based film electrode for the redox reactions of Fe(CN) 6 3−∕4− , Ir(Cl) 6 2−∕3− , and Fe 2+∕3+ , in comparable to typical responses shown on the high-quality, boron-doped nanocrystalline diamond thin-film [120]. Later the electrochemical characteristics of boron-doped diamond powders based film electrodes were investigated by measuring the cyclic voltammetric curves and AC impedance spectra [121].…”

“…Doped diamond particles, mainly boron-doped diamond particles, have been obtained mainly via the overgrowth of insulating diamond particles with boron-doped diamond, solid-state diffusion, and milling [119,120]. For example, boron-doped diamond powder was synthesized under HPHT using B-doped graphite intercalation compositions as carbon sources [121].…”

“…They are thus corrosion-resistant during anodic polarization. In contrast, glassy carbon powders polarized under identical conditions underwent significant microstructural degradation and corrosion [124]. Electrocatalytic oxidation of methanol was tested on the composite based on boron-doped diamond particles (500 nm and 5 μm in diameter) and metallic oxides [125].…”

Lattice Parameter of Polycrystalline Diamond in the Low-Temperature Range

“…Polycrystalline diamond is also reported to be applicable in electrocatalysis [5] and to be suitable for neutron filters [6], heatspreaders [7], for construction of surface acoustic wave devices [8], for radiation dosimetry [9], or for electrochemical detection of trace substances [10].…”

Diamond and Hydrogenated Carbons for Advanced Batteries and Fuel Cells: Fundamental Studies and Applications.

“…2005, 152, E184). In previous work, we prepared and characterized metal/diamond composite electrodes (11)(12)(13). These highly stable and corrosion resistant electrodes were formed by electrodepositing (DC potential) Pt metal on a diamond film surface and then anchoring the particles within a thin secondary diamond layer.…”