172
4 – Electrode reactions
Thus, we will refer to the O 2 /O
2−
couple for an oxygen electrode and to the
Li
+
/Li couple for a lithium electrode.
4.1.3 – Electrode polarization
Polarizing an electrode means that you impose on it a potential E that differs
from its open-circuit potential. The polarization is given by
Π = E − E i=0
If Π > 0, the electrode undergoes an oxidation reaction and carries a positive
current. If Π < 0, the electrode undergoes a reduction reaction and, according
to convention among electrochemists, carries a negative current.
4.1.4 – Electrode overpotential
The electrode overpotential is the polarization of an electrode subject to a single
electrochemical reaction
η = E − E th
4.1.5 – Current density
Current density is the current I per unit surface area S of the electrodeelectrolyte interface:
i
S
I
=
4.2 – Electrochemical kinetics
4.2.1 – Review
L Steady state and transient state
In electrochemistry, the system is in a steady state when the potential, the current, and the concentration of electroactive species are independent of time.
If this is not the case, the system is in a transient state and the concentrations
vary in time according to kinetic equations such as the Fick’s law for diffusion
and the equations for the heterogeneous kinetics of adsorption (see Appendix).
L Kinetic regimes
of charge transfer (or activation), diffusion, and adsorption-desorption. We
In solid-state electrochemistry, the most common kinetic regimes are the regimes
4 – Electrode reactions
Thus, we will refer to the O 2 /O
2−
couple for an oxygen electrode and to the
Li
+
/Li couple for a lithium electrode.
4.1.3 – Electrode polarization
Polarizing an electrode means that you impose on it a potential E that differs
from its open-circuit potential. The polarization is given by
Π = E − E i=0
If Π > 0, the electrode undergoes an oxidation reaction and carries a positive
current. If Π < 0, the electrode undergoes a reduction reaction and, according
to convention among electrochemists, carries a negative current.
4.1.4 – Electrode overpotential
The electrode overpotential is the polarization of an electrode subject to a single
electrochemical reaction
η = E − E th
4.1.5 – Current density
Current density is the current I per unit surface area S of the electrodeelectrolyte interface:
i
S
I
=
4.2 – Electrochemical kinetics
4.2.1 – Review
L Steady state and transient state
In electrochemistry, the system is in a steady state when the potential, the current, and the concentration of electroactive species are independent of time.
If this is not the case, the system is in a transient state and the concentrations
vary in time according to kinetic equations such as the Fick’s law for diffusion
and the equations for the heterogeneous kinetics of adsorption (see Appendix).
L Kinetic regimes
of charge transfer (or activation), diffusion, and adsorption-desorption. We
In solid-state electrochemistry, the most common kinetic regimes are the regimes