3 The Measurements of the Oxygen Reduction Reaction
45
contaminated by the electrolyte. Reference electrodes commonly used in electrochemical testing include standard hydrogen electrodes (SHE), saturated calomel electrodes (SCE), silver/silver chloride electrodes (Ag/AgCl), mercury/mercury oxide
electrodes (Hg/HgO), and Reversible hydrogen electrode (RHE).
The standard hydrogen electrode referred to as “SHE” is a hydrogen electrode
that is reversible under standard conditions. A primary standard reference electrode
for measuring the hydrogen electrode potential of various reversible electrodes. The
platinum-plated platinum sheet was immersed in a solution containing hydrogen ions,
and a platinum-plated platinum sheet was continuously impinged with a stream of
pure hydrogen, and the hydrogen gas escaped from the upper portion. The siphon and
other electrodes on one side can form a battery. The following reversible electrode
reactions were carried out when hydrogen was adsorbed on platinum black and
contacted with an aqueous solution:
1/2H 2 g H
+
a
+
H
+ e
−
(3.27)
According to the Nernst equation, the electrode potential (E H
+ /H 2 ) is related to
hydrogen ion activity (a H
+
) , hydrogen pressure, temperature, etc.
E H + ,H 2 = E
θ
H + ,H 2
+
RT
F
log
a H +
(P H 2 ) 1/2
(3.28)
If the temperature is constant, a H
+
= 1, P H 2 P H2 = 101.325 Pa, specify the electrode
potential of the hydrogen electrode
E H
+ ,H 2 = 0
This electrode is then referred to as a “standard hydrogen electrode.” The hydrogen
electrode is very sensitive when it is applied. To obtain a stable electrode potential,
it must meet strict experimental conditions. The reversible hydrogen electrode is
derived from a standard hydrogen electrode, the difference being that the electrolyte
solution of the reversible hydrogen electrode is identical to the electrolyte solution
of the test system.
If a silver chloride is plated on the silver wire and then immersed in a solution of
chloride, it is a silver–silver chloride electrode. Ag–AgCl electrode structure system
is Ag | AgCl(s) | KCl, the electrode reaction is.
AgCl (s) + e
−
Ag(s) + Cl
−
(l)
(3.29)
Like the calomel electrode, the electrode potential depends on the chloride ion
activity in the solution, i.e.,
E = E
θ
Ag/AgCl −
2.303RT
F
log a Cl
−
(3.30)
45
contaminated by the electrolyte. Reference electrodes commonly used in electrochemical testing include standard hydrogen electrodes (SHE), saturated calomel electrodes (SCE), silver/silver chloride electrodes (Ag/AgCl), mercury/mercury oxide
electrodes (Hg/HgO), and Reversible hydrogen electrode (RHE).
The standard hydrogen electrode referred to as “SHE” is a hydrogen electrode
that is reversible under standard conditions. A primary standard reference electrode
for measuring the hydrogen electrode potential of various reversible electrodes. The
platinum-plated platinum sheet was immersed in a solution containing hydrogen ions,
and a platinum-plated platinum sheet was continuously impinged with a stream of
pure hydrogen, and the hydrogen gas escaped from the upper portion. The siphon and
other electrodes on one side can form a battery. The following reversible electrode
reactions were carried out when hydrogen was adsorbed on platinum black and
contacted with an aqueous solution:
1/2H 2 g H
+
a
+
H
+ e
−
(3.27)
According to the Nernst equation, the electrode potential (E H
+ /H 2 ) is related to
hydrogen ion activity (a H
+
) , hydrogen pressure, temperature, etc.
E H + ,H 2 = E
θ
H + ,H 2
+
RT
F
log
a H +
(P H 2 ) 1/2
(3.28)
If the temperature is constant, a H
+
= 1, P H 2 P H2 = 101.325 Pa, specify the electrode
potential of the hydrogen electrode
E H
+ ,H 2 = 0
This electrode is then referred to as a “standard hydrogen electrode.” The hydrogen
electrode is very sensitive when it is applied. To obtain a stable electrode potential,
it must meet strict experimental conditions. The reversible hydrogen electrode is
derived from a standard hydrogen electrode, the difference being that the electrolyte
solution of the reversible hydrogen electrode is identical to the electrolyte solution
of the test system.
If a silver chloride is plated on the silver wire and then immersed in a solution of
chloride, it is a silver–silver chloride electrode. Ag–AgCl electrode structure system
is Ag | AgCl(s) | KCl, the electrode reaction is.
AgCl (s) + e
−
Ag(s) + Cl
−
(l)
(3.29)
Like the calomel electrode, the electrode potential depends on the chloride ion
activity in the solution, i.e.,
E = E
θ
Ag/AgCl −
2.303RT
F
log a Cl
−
(3.30)