Faraday impedance analysis of the process at the boundary between a cadmium-selective electrode and a CdSO₄ solution

Faraday impedance measurements have been made at alternating current frequencies of 0.01–200 kHz, and tests have been done on the process in the system provided by a Cd-SE with a CdSO₄ solution. There is a two-stage mechanism: in the first, a surface film is formed conducting Cd²⁺ cations, and in the second, there are solid-state reactions in the SE membrane. An equivalent circuit is proposed that adequately describes the processes at the electrode, and basic parameters and diffusional and kinetic characteristics have been calculated for condensed and uncondensed electrodes. The diffusion and kinetic parameters show that the diffusion rate increases with the electrolyte concentration, with c ₀ D ^1/2 tending to increase, where c ₀ and D are the initial molar concentration and diffusion coefficient of the potential-determining particles. The transport parameters and the exchange-current density have higher values for condensed electrodes.