THERMOIMPEDANCE OF THE REVERSIBLE ELECTRODE FE[(CN)(6)](3-)/FE[(CN)(6)](4-)

Thermoimpedance of the reversible system Fe[(CN)(6)](3-)/Fe[(CN)(6)](4-) is measured in the frequency range from 0.005 to 640 Hz. Under the conditions of equilibrium it is possible to write Z(phi)/Z(i) = -Z(e)(-1), where Z(phi) and Z(i) are thermoimpedances at a constant potential and current, respectively, and Z(e) is an electrochemical impedance. In the region of anodic and cathodic limiting currents, thermoimpedance is governed by the temperature dependence of the diffusion coefficient and the thickness of the diffusion layer. The frequency spectra of thermoimpedance and corresponding equivalent circuits are presented. Activation energies of diffusion for anodic (20 kT mol(-1)) and cathodic (16 kT mol(-1)) limiting currents are evaluated.