The characterization of porous electrodes by impedance measurements

Impedances of a gold-powder and a Raney-gold electrode were measured over a wide frequency range, and were found to be very similar to those of cylindrical pore of finite depth. The simulation calculation for sphere-packed electrode impedance was performed. It was observed that even though each sphere-layer shows the impedance related to an occluded pore-shape, the overall impedance is similar to that of a cylindrical pore electrode. When the penetration depth approaches the pore depth, the shape of the pore wall has little influence on the impedance. Thus, impedance measurement techniques can be applied to porous electrodes of more intricate pore-texture, and evaluate the radius, depth and pore number of its equivalent cylindrical pore electrode. These values determined for a Raney-gold electrode are in very good agreement with those determined by other methods. The case of a more realistic fuel cell electrode such as Raney-nickel with a metal-electrolyte-gas system, was also tentatively examined.