Comparison of transmissive permeable and reflective impermeable interfaces between electrode and electrolyte

This article described the basic concepts of the permeable boundary (PB) and impermeable boundary (IPB) conditions between electrode and electrolyte that are essential in studying diffusion and migration of ions through the electrode for electrochemical devices. The transmission line models (TLMs) were introduced to explain the boundary conditions at the electrode/electrolyte interfaces. The impedance data were simulated based upon the TLMs for PB and IPB conditions, giving attention to the different behaviors of low-frequency impedance. In addition, this article explained that the electrodes used for fuel cells and batteries can be classified according to the PB and IPB conditions.

     

Kinetics of oxygen reduction on porous mixed conducting (La0.85Sr0.15)0.9MnO3 electrode by ac-impedance analysis

The oxygen reduction reaction on mixed conducting (La_0.85Sr_0.15)_0.9MnO₃ electrodes with various porosities was investigated by analysis of the ac-impedance spectra. To attain a mixed electronic/ionic conducting state of (La_0.85Sr_0.15)_0.9MnO₃ with high oxygen vacancy concentration, the electrode specimen was purposely subjected to cathodic polarisation. The ac-impedance spectrum clearly showed a straight line inclined at a constant angle of 45° to the real axis in the high-frequency range, followed by an arc in the low-frequency range, i.e. it exhibited the Gerischer behaviour. This strongly indicates that oxygen reduction on the mixed conducting electrode involves diffusion of oxygen vacancy through the electrode coupled with the electron exchange reaction between oxygen vacancies and gaseous oxygen (charge transfer reaction) at the electrode/gas interface. It was further recognised that the two-dimensional electrochemical active region for oxygen reduction extends from the origin of the three-phase boundaries (TPBs) among electrode, electrolyte and gas into the electrode/gas interface segments, which is on average approximately 0.7 to 1.1 μm in length below the electrode porosity 0.12. Based from the fact that the ac-impedance spectrum deviated more significantly from the Gerischer behaviour with increasing electrode porosity above 0.22, it is proposed that due to the increased length of TPBs, the rate of the overall oxygen reduction on the highly porous electrode is mainly determined by the charge transfer reaction at the TPBs, and the subsequent diffusion of oxygen vacancy occurs facilely through the electrode.     

Comparison of transmissive permeable and reflective impermeable interfaces between electrode and electrolyte

This article described the basic concepts of the permeable boundary (PB) and impermeable boundary (IPB) conditions between electrode and electrolyte that are essential in studying diffusion and migration of ions through the electrode for electrochemical devices. The transmission line models (TLMs) were introduced to explain the boundary conditions at the electrode/electrolyte interfaces. The impedance data were simulated based upon the TLMs for PB and IPB conditions, giving attention to the different behaviors of low-frequency impedance. In addition, this article explained that the electrodes used for fuel cells and batteries can be classified according to the PB and IPB conditions.