THE EFFECT OF SURFACE-ROUGHNESS ON THE AC-IMPEDANCE OF PALLADIUM IN SULFURIC-ACID

The ac impedance of palladium foil and palladium-plated AISI 304 stain less steel in deaerated 1 mol l-1 H2SO4 was determined at the open-cir cuit potential of each specimen. The surface of the plated electrode w as rough and exhibited irregular features associated with the original surface of the substrate. Nevertheless, Nyquist plots for the palladi um and palladium-plated electrodes were of a similar shape, indicating that the electrochemical behavior of the plated stainless steel resem bled that of palladium. In both cases, Bode plots of log absolute valu e of Z as a function of log omega exhibited a single linear region of slope -0.9 over at least four decades of frequency. It was shown that the data can be represented in terms of an equivalent circuit containi ng a capacitance associated with the double layer and an apparent impe dance due to surface roughness.