Nicola Comisso

Electrodes Coated by Passive Oxide Films with a Thickness Profile: Modeling and Measurement of the Impedance Response

The impedance of a rectangular electrode coated by a resistive film is calculated for the cases of linear and exponential thickness profiles along the electrode length. The local film capacity and local film resistance of each surface element are assumed to be inversely and directly proportional to local film thickness, respectively. Experimental model electrodes are prepared by anodizing niobium or tantalum rectangular sheets with a setup allowing the progressive extraction of the electrode from the electrolyte, at a constant rate, while the cell voltage is increased according to a suitable program. The impedance of the coated electrode, measured at a potential close to the lowest anodization potential, agrees well with theory. In particular, the plot of the ohmic resistance corrected phase angle vs frequency shows a minimum. The effect of experimental parameters such as thickness profile or solution concentration can be interpreted on the basis of the calculations.

Electrodeposition of Cu + PdO and ( Cu – Pd ) + PdO Composites

The codeposition of PdO particles with a Cu matrix has been investigated with the aim of extending the composite deposition procedure to the preparation of materials potentially capable of catalyzing the low temperature combustion of methane. Cu + PdO composites with a low dispersed phase content were obtained from either basic pyrophosphate or acid sulfate baths. Codeposition of PdO particles with a Cu-Pd alloy matrix was effectively achieved by electrolyzing suspensions of PdO in solutions containing both Cu 2+ and Pd 2+ ions, with large [Cu 2+ ]/[Pd 2+ ] ratios. (Cu-Pd) + PdO deposits with 20-25 Pd atom % were obtained in which only 1-2 atom % of Pd were alloyed in the matrix. These (Cu-Pd) + PdO composites were mechanically stable and highly porous throughout their thickness (their pore volume being ca. 60% of the total volume). Their true surface area was some thousands of times higher than their geometric area.