291
Characterization and Diagnosis Techniques
the Fe(II)-N x species attached to the particles. The specific capacitances for
these two materials should be different because they provide double-layer
and pseudocapacitance capabilities, respectively. For carbon particles, the
double-layer charge is 2.90 × 10 –3 C in the potential range of 0.05 to 1.0V, and
the weight of carbon particles is 0.0000286 g according to the 95:5% weight
percentage ratio of the carbon and Fe active center in the electrode layer.
Therefore, its specific capacitance can be calculated to be 107 F.g –1
For the Fe(II)-Nx/Fe(III)-Nx redox wave that is electrochemically active in
the potential range of ~0.56 to 0.76 V (E 2 – E 1 = 0.20 V in this case), according
to the definition of pseudocapacitance provided in Chapter 3, the specific
capacitance of the electrochemical active material
Q
(C ) =
sp
,
pc sp
m E 2 − E 1
sp
where Q sp = 4.4 × 10 –4 C, m sp = 1.40 × 10–6 g, and |E 2 – E 1 | = 0.2 V] can be
calculated as 1570 F.g –1 , which is much higher than that of carbon particles
(107 F.g –1 ). However, due to both its low quantity in the electrode layer and
its limited reaction potential range, its contribution to the apparent specific
capacitance is still small.
Note that Equation (7.19) is for measurements using a three-electrode
electrochemical cell. For a two-electrode test cell based on Equation (7.14),
Equation (7.19) will become Equation (7.20) if the cell is symmetric:
Q + Q
dl
pc
C m = 2
(7.20)
V V
2 − 1
7.4 Charging–Discharging Curve
Characterization via the charging–discharging curve (CDC) is one of the
most reliable approaches to determine capacitance energy density, power
density, equivalent series resistance, and cycle life of a supercapacitor. In
recording charging–discharging curves, the conventional three-electrode or
two-electrode test cells can be employed, depending on availability, similar
to the procedure described above for CV characterization. Again, both symmetric and asymmetric supercapacitors can be characterized by this CDC
technique. However, for characterizing cycle life of a supercapacitor, twoelectrode test cells are favorable because they more closely resemble practical
operating conditions.
Characterization and Diagnosis Techniques
the Fe(II)-N x species attached to the particles. The specific capacitances for
these two materials should be different because they provide double-layer
and pseudocapacitance capabilities, respectively. For carbon particles, the
double-layer charge is 2.90 × 10 –3 C in the potential range of 0.05 to 1.0V, and
the weight of carbon particles is 0.0000286 g according to the 95:5% weight
percentage ratio of the carbon and Fe active center in the electrode layer.
Therefore, its specific capacitance can be calculated to be 107 F.g –1
For the Fe(II)-Nx/Fe(III)-Nx redox wave that is electrochemically active in
the potential range of ~0.56 to 0.76 V (E 2 – E 1 = 0.20 V in this case), according
to the definition of pseudocapacitance provided in Chapter 3, the specific
capacitance of the electrochemical active material
Q
(C ) =
sp
,
pc sp
m E 2 − E 1
sp
where Q sp = 4.4 × 10 –4 C, m sp = 1.40 × 10–6 g, and |E 2 – E 1 | = 0.2 V] can be
calculated as 1570 F.g –1 , which is much higher than that of carbon particles
(107 F.g –1 ). However, due to both its low quantity in the electrode layer and
its limited reaction potential range, its contribution to the apparent specific
capacitance is still small.
Note that Equation (7.19) is for measurements using a three-electrode
electrochemical cell. For a two-electrode test cell based on Equation (7.14),
Equation (7.19) will become Equation (7.20) if the cell is symmetric:
Q + Q
dl
pc
C m = 2
(7.20)
V V
2 − 1
7.4 Charging–Discharging Curve
Characterization via the charging–discharging curve (CDC) is one of the
most reliable approaches to determine capacitance energy density, power
density, equivalent series resistance, and cycle life of a supercapacitor. In
recording charging–discharging curves, the conventional three-electrode or
two-electrode test cells can be employed, depending on availability, similar
to the procedure described above for CV characterization. Again, both symmetric and asymmetric supercapacitors can be characterized by this CDC
technique. However, for characterizing cycle life of a supercapacitor, twoelectrode test cells are favorable because they more closely resemble practical
operating conditions.