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4 – Electrode reactions
2 Electrical phenomena related to the movement of charge carriers due
to an applied ac electric field (domains A and B); for example,
• the bulk response of electrolyte (A), which corresponds to intragrain ionic migration phenomena. These fast phenomena appear at
high frequencies.
• the interface response at grain boundaries (B), which correspond to
inter-grain ionic migration phenomena. These phenomena are slower and appear at intermediate frequencies. The influence of grain
boundaries leads to a relative increase in the electrical resistance of
ceramics with respect to the corresponding single crystals. We thus
speak of the “blocking effect” of carriers. These blocking effects
depend strongly on the ceramic microstructure.
2 Electrochemical phenomena involving complex reaction processes
such as diffusion, adsorption, and charge transfer (domain C), which
together constitute the electrode polarization. These much slower
phenomena appear at low frequencies. The form of the impedance
diagram depends on limiting phenomena at the electrodes.
In the case of an oxygen-diffusion-limited electrode, the polarization
appears in the Nyquist representation in the form of a line with slope ½,
which is characteristic of this type of mechanism.
c. If we assume that the oxygen activity X O is an increasing function of
oxygen partial pressure, the expression for impedance Z shows that the
impedance at a fixed frequency decreases with oxygen partial pressure.
Solution 4.2 – Study of oxygen-electrode reaction
1. The phenomena observed at high frequencies are related to the properties
of the electrolyte. The inductance reflects inductive parasitic effects. At low
frequency, we observe the overall reaction at the oxygen electrode. Some
of these reactions depend on the thickness and on the surface area of the
electrolyte surface, whereas others depend solely on the electrode surface.
Varying the geometric factor allows us to differentiate between these reactions. Furthermore, as opposed to the electrolyte resistance, the electrode
reaction depends on the oxygen partial pressure. Controlling this pressure
thus constitutes another way to identify the electrode reaction.
4 – Electrode reactions
2 Electrical phenomena related to the movement of charge carriers due
to an applied ac electric field (domains A and B); for example,
• the bulk response of electrolyte (A), which corresponds to intragrain ionic migration phenomena. These fast phenomena appear at
high frequencies.
• the interface response at grain boundaries (B), which correspond to
inter-grain ionic migration phenomena. These phenomena are slower and appear at intermediate frequencies. The influence of grain
boundaries leads to a relative increase in the electrical resistance of
ceramics with respect to the corresponding single crystals. We thus
speak of the “blocking effect” of carriers. These blocking effects
depend strongly on the ceramic microstructure.
2 Electrochemical phenomena involving complex reaction processes
such as diffusion, adsorption, and charge transfer (domain C), which
together constitute the electrode polarization. These much slower
phenomena appear at low frequencies. The form of the impedance
diagram depends on limiting phenomena at the electrodes.
In the case of an oxygen-diffusion-limited electrode, the polarization
appears in the Nyquist representation in the form of a line with slope ½,
which is characteristic of this type of mechanism.
c. If we assume that the oxygen activity X O is an increasing function of
oxygen partial pressure, the expression for impedance Z shows that the
impedance at a fixed frequency decreases with oxygen partial pressure.
Solution 4.2 – Study of oxygen-electrode reaction
1. The phenomena observed at high frequencies are related to the properties
of the electrolyte. The inductance reflects inductive parasitic effects. At low
frequency, we observe the overall reaction at the oxygen electrode. Some
of these reactions depend on the thickness and on the surface area of the
electrolyte surface, whereas others depend solely on the electrode surface.
Varying the geometric factor allows us to differentiate between these reactions. Furthermore, as opposed to the electrolyte resistance, the electrode
reaction depends on the oxygen partial pressure. Controlling this pressure
thus constitutes another way to identify the electrode reaction.