46
C. Juhong et al.
The detailed preparation method of the Ag/AgCl electrode is a thermal decomposition method and an electroplating method, wherein the electroplating method is
simple, and the process is as follows: First, the silver wire is taken and the surface
oil is first washed with acetone, and if silver is plated on the silver wire, it is required
first elute with ammonia water and then rinse carefully with distilled water. Then, the
silver electrode was used as the anode, the platinum wire was used as the cathode, and
a layer of silver chloride was electroplated in a 1 mol·L
−1 hydrochloric acid solution
for 30 min (current density of 2 mA.cm
−2 ), and finally rinsed with distilled water.
The electrode produced is purple-brown and this electrode can be applied directly
without a liquid junction.
If platinum wire is used as the substrate, silver plating should first be applied
to the platinum wire. Platinum wire silver plating method: First, prepare a silver
plating solution (AgNO 3 3 g, KCl 60 g, concentrated ammonia water 7 mL, add
water to make 100 mL solution), then a platinum wire to be plated as a cathode,
another platinum wire as an anode, and a series of about 2000 variable resistor,
voltage is set to 4 V, electroplate at 0.5 mA.cm
−2 current density for 0.5 h. Wash the
silver-plated electrode and then plate a layer of silver chloride in the same manner
as above.
In 0.1 mol·L
−1 KCl solution, the electrode potential of Ag/AgCl electrode is equal
to 0.2880 V (SHE, 25 °C). The electrode potential of silver–silver chloride electrode
is stable, reproducible, simple in structure and convenient to use. It is also relatively
stable in seawater, so it is widely used for ship cathodic protection in addition to its
application in the laboratory.
The calomel electrode is one of the most widely used reference electrodes in
the laboratory. It consists of metallic mercury and mercurous chloride (Hg 2 Cl 2 ) and
potassium chloride solution.
Hg | Hg 2 Cl 2 (saturated), KCl (X mol·L
−1) (X represents the molar concentration
of KCl in solution.)
HgCls + 2 e
−
2Hgl + 2 Cl
−
(3.31)
E = E
θ
Hg 2 Cl 2 /Hg −
2.303RT
F
log a Cl
−
(3.32)
A platinum wire is sealed in the inner glass tube, the platinum wire is inserted into
pure mercury (thickness 0.5 to 1 cm), a paste of mercurous chloride and mercury
is placed underneath, and potassium chloride is placed in the outer glass tube. The
solution constitutes the calomel electrode. The contact portion of the lower end of the
electrode with the solution to be tested is a porous substance such as a sintered ceramic
core or a glass sand core or a capillary channel. When the temperature is fixed, the
electrode potential of the calomel electrode is determined by the chloride ion activity.
When the chloride ion activity is constant, the electrode potential is also constant,
regardless of the pH of the solution to be tested. Different concentrations of potassium
chloride solution can make its potential have different constant values. At 25 °C,
different concentrations of potassium chloride solution can have different potentials
C. Juhong et al.
The detailed preparation method of the Ag/AgCl electrode is a thermal decomposition method and an electroplating method, wherein the electroplating method is
simple, and the process is as follows: First, the silver wire is taken and the surface
oil is first washed with acetone, and if silver is plated on the silver wire, it is required
first elute with ammonia water and then rinse carefully with distilled water. Then, the
silver electrode was used as the anode, the platinum wire was used as the cathode, and
a layer of silver chloride was electroplated in a 1 mol·L
−1 hydrochloric acid solution
for 30 min (current density of 2 mA.cm
−2 ), and finally rinsed with distilled water.
The electrode produced is purple-brown and this electrode can be applied directly
without a liquid junction.
If platinum wire is used as the substrate, silver plating should first be applied
to the platinum wire. Platinum wire silver plating method: First, prepare a silver
plating solution (AgNO 3 3 g, KCl 60 g, concentrated ammonia water 7 mL, add
water to make 100 mL solution), then a platinum wire to be plated as a cathode,
another platinum wire as an anode, and a series of about 2000 variable resistor,
voltage is set to 4 V, electroplate at 0.5 mA.cm
−2 current density for 0.5 h. Wash the
silver-plated electrode and then plate a layer of silver chloride in the same manner
as above.
In 0.1 mol·L
−1 KCl solution, the electrode potential of Ag/AgCl electrode is equal
to 0.2880 V (SHE, 25 °C). The electrode potential of silver–silver chloride electrode
is stable, reproducible, simple in structure and convenient to use. It is also relatively
stable in seawater, so it is widely used for ship cathodic protection in addition to its
application in the laboratory.
The calomel electrode is one of the most widely used reference electrodes in
the laboratory. It consists of metallic mercury and mercurous chloride (Hg 2 Cl 2 ) and
potassium chloride solution.
Hg | Hg 2 Cl 2 (saturated), KCl (X mol·L
−1) (X represents the molar concentration
of KCl in solution.)
HgCls + 2 e
−
2Hgl + 2 Cl
−
(3.31)
E = E
θ
Hg 2 Cl 2 /Hg −
2.303RT
F
log a Cl
−
(3.32)
A platinum wire is sealed in the inner glass tube, the platinum wire is inserted into
pure mercury (thickness 0.5 to 1 cm), a paste of mercurous chloride and mercury
is placed underneath, and potassium chloride is placed in the outer glass tube. The
solution constitutes the calomel electrode. The contact portion of the lower end of the
electrode with the solution to be tested is a porous substance such as a sintered ceramic
core or a glass sand core or a capillary channel. When the temperature is fixed, the
electrode potential of the calomel electrode is determined by the chloride ion activity.
When the chloride ion activity is constant, the electrode potential is also constant,
regardless of the pH of the solution to be tested. Different concentrations of potassium
chloride solution can make its potential have different constant values. At 25 °C,
different concentrations of potassium chloride solution can have different potentials