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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.

A corrosion-resistant electrocatalyst support was prepared by overcoating high surface-area diamond powder ͑3-6 nm diameter, 250 m 2 /g͒ with a thin layer of boron-doped ultrananocrystalline diamond ͑B-UNCD͒ by microwave plasma-assisted chemical vapor deposition. This core-shell approach produces electrically conducting ͑0.4-0.5 S/cm͒ and high surface-area ͑150-170 m 2 /g͒ diamond powder ͑B-UNCD-D͒. Accelerated degradation testing was performed by thermogravimetric analysis ͑TGA͒ to assess the oxidation resistance ͑i.e., corrosion resistance͒ of powder in the absence and presence of nanoscale Pt. The oxidation onset temperature for B-UNCD-D powder decreased with the Pt loading from 0 to 30 wt % ͑Pt/C͒. However, compared with the bare powder, the rate of carbon consumption was significantly greater for Pt-͑XC-72͒ as compared to the platinized diamond powder. For example, the temperature of the maximum carbon consumption rate, T d , occurred at 426°C for Pt-͑XC-72͒ ͑20% Pt/C͒, which was 295°C lower than the T d for bare XC-72. In contrast, T d for Pt-͑B-UNCD-D, 20% Pt/C͒ was 558°C; a temperature that was only 62°C lower than that for bare diamond. Isothermal oxidation at 300°C for 5 h produced negligible weight loss for Pt-UNCD-D ͑20% Pt/C͒ while a 75% weight loss was observed for Pt-͑XC-72͒ ͑20% Pt/C͒. The results clearly demonstrate that platinized diamond is more resistant to gas phase oxidation than is platinized Vulcan at elevated temperatures.With the advantages of low temperature operation, zero emission, and rapid start-up, polymer electrolyte membrane fuel cells ͑PEMFCs͒ are promising power sources for transportation. 1-4 One factor limiting the application of PEMFCs is the stability of the carbon electrocatalyst support. Vulcan XC-72 carbon black is commonly used as a support because of its high electrical conductivity ͑ Ͼ 0.5 S/cm͒and specific surface area ͑250 m 2 /g͒. This carbon is susceptible to electrochemical corrosion during extended operation and automotive cycling, which leads to performance loss. 5-7 The causes for this include high water content, low pH ͑Ͻ1͒, high temperature ͑50-90°C͒, high potential ͑0.6-1.2 V͒, and high oxygen concentration. Carbon corrosion does not occur continuously during operation, but is more problematic during start-up or when the anode is fuel-starved. [8][9][10][11] Oxidation of the electrocatalyst-loaded carbon ͑e.g., Pt͒ to form CO and/or CO 2 is catastrophic for fuel cell performance because the lost carbon leads to increased ohmic resistance and reduced electrocatalytic activity.In the presence of Pt, the rate of carbon corrosion is higher than for bare carbon at temperatures of Ͻ500°C. For example, Roen et al. showed that the rate of CO 2 production was higher for Pt coated than for bare carbon even at temperatures as low as 50°C. 6 Furthermore, the CO 2 generation rate increased incrementally with the Pt loading ͑0, 10, and 39% Pt/C͒. Carbon oxidation in the presence of Pt involves multiple steps. For example, it has been shown that in the presence of Pt, C s...

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This paper reports on preliminary tests of the performance of boron-doped diamond powder (BDDP) as a stationary phase in electrochemically modulated liquid chromatography (EMLC). EMLC manipulates retention through changes in the potential applied (Eappl) to a conductive packing. Porous graphitic carbon (PGC) has routinely been utilized as a material in EMLC separations. Herein the utility of BDDP as a stationary phase in EMLC was investigated and its stability, both compositionally and microstructurally, relative to PGC was compared. The results show that BDDP is stable over a wide range of Eappl values (i.e., −1.2 to +1.2 V vs. Ag/AgCl, sat’d NaCl). 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. The potential for this methodology to provide a means to advance the understanding of molecular adsorption and retention mechanisms on carbonaceous materials is briefly discussed.