Pulsed galvanostatic deposition of Pt particles on microcrystalline and nanocrystalline diamond thin-film electrodes I. Characterization of as-deposited metal/diamond surfaces

The pulsed galvanostatic deposition of nanometer-sized Pt particles on electrically conducting microcrystalline and nanocrystalline diamond thin-film electrodes is reported. The deposition was studied as a function of pulse number (10-50) and current density (0.50-1.50 mA cm^-2) at the two morphologically different forms of diamond. The deposition of catalyst particles using ten 1 s pulses (duty cycle 50%) at a current density of 1.25 mA cm ^-2 (geometric area) produced the smallest nominal particle size and the highest particle coverage on both diamond surfaces. Secondary electron micrographs revealed metal particle deposition over much of the diamond surface, a nominal particle size of 43 ± 27 nm [relative standard deviation (RSD) = 63%] for microcrystalline and 25 ± 25 nm (RSD = 100%) for nanocrystalline diamond, and a nominal particle coverage of 7.5 (±0.9) × 109 cm^-2 for microcrystalline and 1.9 (±1.0) × 10¹⁰ cm^-2 for nanocrystalline diamond. Deposition under these conditions resulted in the most efficient utilization of the metal catalyst for H⁺ adsorption, based on the electrochemically active Pt area normalized to the estimated metal loading. Typical specific surface areas of 10-50 m²/g Pt were calculated, which compare favorably to values obtained at sp² electrodes, like carbon and graphite. The influence of the diamond electrode microstructural and electronic properties on the formation of dimensionally uniform metal adlayers is discussed.