Microstructural stability of electrically conducting diamond powder as probed using electrochemical methods and in situ raman spectroscopy

Electrochemical and in situ Raman spectroscopic measurements were made on boron-doped diamond powder (8-12 m diam., 0.63 m²g, 2 Scm) to assess the dimensional stability and corrosion resistance during potentiostatic polarization in acid. The powder was prepared by overcoating diamond abrasive with a layer of boron-doped microcrystalline diamond. The polarizations were performed at room temperature or 80C in either 0.1 M HClO₄ or 0.1 M H₂SO₄ from 1.0-1.4 V vs. AgAgCl. Cyclic voltammetric measurements were made on the powders before and after polarization to probe for microstructural damage and ohmic resistance changes. Comparison measurements were made with the sp² carbon, acetylene black (68 m²g, 2 Scm). Electrodes were prepared by casting a powder slurry on a glass slide with Nafion serving as the binder. No microstructural damage, alteration of the electrical conductivity or corrosion of the diamond powder was detected during polarization under the severest test conditions (ca. 1.4 V in 0.1 M H ₂SO₄ at 80C). In the Raman spectra, the diamond phonon line position, intensity and line width were unaffected by the polarization, consistent with excellent dimensional stability and corrosion resistance. In contrast, microstructural changes were seen for acetylene black during identical testing. Polarization at 1.4 V in 0.1 M H₂SO₄ at 80C produced increases in the surface area of the acetylene black due to surface oxidation and the associated microstructural damage. In situ Raman spectra confirmed the microstructural damage as the DG (I₁₃₅₀I ₁₅₈₀) peak intensity ratio increased from 1.03 to 1.09 during a 120-min room temperature polarization in 0.1 M HClO₄ at 1.4 V.