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Electrochemical Supercapacitors for Energy Storage and Delivery
7.2 Electrochemical Cell Design and Fabrication
For supercapacitor characterization, testing, and diagnosis purposes, the
electrochemical cell designs are classified as the conventional three-electrode
cell and the two-electrode test cell. The former is used for fast screening and
characterization of electrode materials and their associated electrode layer
structure and optimization. The latter is used to validate supercapacitor performance under real operating conditions.
7.2.1 Conventional Three-Electrode Cell Design and Fabrication
Figure 7.1 shows the design for a conventional three-electrode electrochemical cell. The three electrodes are: (1) the electrode material-coated working
electrode made of a carbon material such as glassy carbon or a stable metal
such as Au or Pt, (2) the counter electrode (Pt foil or net), and (3) a reference
electrode such as a normal hydrogen electrode (NHE), reversible hydrogen
electrode (RHE), or saturated calomel electrode (SCE). Note that the NHE
uses large surface Pt black as the metal electrode and 1.0 M H + aqueous solution (such as 0.5 M H 2 SO 4 ) as the electrolyte. Its electrode potential is defined
as zero at 1.0 atm at any temperature.
The gas inlet and outlet shown in Figure 7.1 are used for gas purging. In
particular, to avoid possible oxygen interference from dissolved air during
surface CV measurements, N 2 gas is used to deaerate the electrolyte solution
for 30 to 60 min [1]. In addition, a thermometer port monitors the temperature of the electrolyte solution. For controlling the temperature, the whole
cell is emerged into a thermal bath that allows the temperature of the liquid
to be adjusted to the desired level.
To prepare the working electrode layer, the electrode active material such as
carbon or pseudocapacitive materials are mixed with conductive carbon and
isopropanol for 30 to 60 min to form an ink. A desired amount of this ink (several microliters for a small electrode surface area such as 0.2 to 0.5 cm 2 ) is pipetted gradually onto a prepolished electrode with a microsyringe. After drying,
several microliters of diluted Nafion solution is used to cover the coated electrode to form a uniform electrode layer for electrochemical measurements.
7.2.2 Two-Electrode Test Cell Design and Assembly
Figure 7.2 shows the two-electrode test cell reported by Tsay at al. [1]. It has
active electrode surfaces for both positive and negative electrodes. These two
electrodes are placed between two metal plates within Teflon plates. The
metal plates serve as the current collectors and at the same time as holders to
tighten the electrode separator, containing the electrolyte–electrode assembly (ESEA) together. One metal plate is fitted with three screws in a threepoint geometry that ensures a better pressure balance than a four-point
Electrochemical Supercapacitors for Energy Storage and Delivery
7.2 Electrochemical Cell Design and Fabrication
For supercapacitor characterization, testing, and diagnosis purposes, the
electrochemical cell designs are classified as the conventional three-electrode
cell and the two-electrode test cell. The former is used for fast screening and
characterization of electrode materials and their associated electrode layer
structure and optimization. The latter is used to validate supercapacitor performance under real operating conditions.
7.2.1 Conventional Three-Electrode Cell Design and Fabrication
Figure 7.1 shows the design for a conventional three-electrode electrochemical cell. The three electrodes are: (1) the electrode material-coated working
electrode made of a carbon material such as glassy carbon or a stable metal
such as Au or Pt, (2) the counter electrode (Pt foil or net), and (3) a reference
electrode such as a normal hydrogen electrode (NHE), reversible hydrogen
electrode (RHE), or saturated calomel electrode (SCE). Note that the NHE
uses large surface Pt black as the metal electrode and 1.0 M H + aqueous solution (such as 0.5 M H 2 SO 4 ) as the electrolyte. Its electrode potential is defined
as zero at 1.0 atm at any temperature.
The gas inlet and outlet shown in Figure 7.1 are used for gas purging. In
particular, to avoid possible oxygen interference from dissolved air during
surface CV measurements, N 2 gas is used to deaerate the electrolyte solution
for 30 to 60 min [1]. In addition, a thermometer port monitors the temperature of the electrolyte solution. For controlling the temperature, the whole
cell is emerged into a thermal bath that allows the temperature of the liquid
to be adjusted to the desired level.
To prepare the working electrode layer, the electrode active material such as
carbon or pseudocapacitive materials are mixed with conductive carbon and
isopropanol for 30 to 60 min to form an ink. A desired amount of this ink (several microliters for a small electrode surface area such as 0.2 to 0.5 cm 2 ) is pipetted gradually onto a prepolished electrode with a microsyringe. After drying,
several microliters of diluted Nafion solution is used to cover the coated electrode to form a uniform electrode layer for electrochemical measurements.
7.2.2 Two-Electrode Test Cell Design and Assembly
Figure 7.2 shows the two-electrode test cell reported by Tsay at al. [1]. It has
active electrode surfaces for both positive and negative electrodes. These two
electrodes are placed between two metal plates within Teflon plates. The
metal plates serve as the current collectors and at the same time as holders to
tighten the electrode separator, containing the electrolyte–electrode assembly (ESEA) together. One metal plate is fitted with three screws in a threepoint geometry that ensures a better pressure balance than a four-point