Charge transfer interfaces

By comparing impedance results for polypyrrole in electrolyte-polymer-electrolyte and electrode-polymer-electrolyte systems, Des-louis et alm have shown that the charge-transfer resistance in the latter case can contain contributions from both interfaces. Charge-transfer resistances at the polymer/electrode interface were about five times higher than those at the polymer/solution interface. Thus the assignments made by Albery and Mount,203 and by Ren and Pickup145 are supported, with the caveat that only the primary source of the high-frequency semicircle was identified. Contributions from the polymer/solution interface, and possibly from the bulk, are probably responsible for the deviations from the theoretical expressions/45... 

Interestingly, this forward current is not controlled by the interface charge-transfer kinetics but entirely by the diffusion and recombination of holes injected into the valence band. This was demonstrated by using differently doped Si electrodes having different diffusion lengths for holes. 

An electrode may be defined as a solid electron conductor which is in contact with a liquid (solid, gaseous) ion conductor (electrolyte). At the interface charge transfer reactions take place. During corrosion processes this charge transfer involves anodic and cathodic partial reactions of various kinds which are dependent on many parameters and which have to be taken into account when designing an electrode. 

When the above conditions of effects of convection and migration are realized, the resulting current is limited only by the diffusion-driven transport of the electroactive species to the electrode-solution interface. At the interface charge transfer reactions take place that can be studied as a function of the electrochemical potential (Fig. 4). That experimental situation contains the fundamental premise of the traditional impedance analysis - make mass-transport effect on interfacial impedance exclusively diffusion limited (Ldiff) and investigate the interfacial kinetic phenomena composed of the diffusion and electrochemical reaction (discharge or electrolysis Rqi) impedances that can be combined in the so-caUed Faradaic impedance. 

Pana O, Soran ML, Leostean C et al (2012) Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles. J Appl Phys 111 044309... 

Figure 3.51 shows the impedance spectra for a Pt/FTO sandwich cell at different bias potentials reported by Hauch and Georg.The impedance element on the left of the spectrum (high frequencies) is the Pt/ electrolyte interface (charge-transfer resistance and double layer capacitance) on the right (low frequencies) there is the Nernst diffusion impedance. The diameter of the high frequency semicircle in the impedance... 

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