6 Application of Oxygen Reduction Catalysts
225
thickness of the catalyst layer is 50 μm and the geometric area of the electrode is
0.2475 cm
2 (A geo = 0.2475 cm
2 ), then the real area of the catalyst layer (A real ) is the
sum of the geometric area of the electrode (A geo ) and the side area of the catalyst
layer (A side ). At present, it is impossible to measure the thickness of catalyst thin
layer accurately when measuring oxygen reduction with rotating disk electrode or
ring disk electrode. When calculating the limiting current density of catalyst oxygen
reduction reaction, it is still calculated according to the geometric area of electrode.
Thus, the calculated limiting current density is greater than 6 mA cm
−2 (as shown
in Eqs. 6.2.3–6.7, 6.2.3–6.8 and 6.2.3–6.9).
A real = A geo + A side = 0.2475cm
2
+ 0.005 ∗ 3.14 ∗ 0.56 cm
2
= 0.2563 cm
2
(6.10)
i d = 0.62nF D
2/3
0 ω
1/2 v
−1/6 C 0 A real = 6 ∗ 0.2563 = 1.538 mA
(6.11)
i d / A geo = 1.538 mA / 0.2475 cm
2
= 6.214 mA cm
−2
(6.12)
6.2 Application in Metal-Air Battery
6.2.1 Overview of Metal-Air Batteries
The so-called metal-air battery refers to a kind of “semi-fuel cell” with the characteristics of both primary cell and fuel cell. The negative electrode of the battery is
metal, the positive electrode of the battery is air electrode, and electrolyte is between
the positive and negative electrodes of the battery [37–39].
Electrolytes can be divided into three types according to the reaction characteristics of metal negative electrodes: aqueous, nonaqueous and aqueous–nonaqueous
mixed. Metal negative electrode of metal-air battery acts like fuel in fuel cell. Metalair battery is also called metal fuel cell. The biggest difference with primary battery
is that the positive active material of metal-air battery is air, the air electrode only
accounts for a small part of the battery volume, and the vacant position can carry a
large amount of active negative metal, so that the metal-air battery has a large energy
density. The biggest difference with fuel cells is that the metal fuel is built-in and the
negative electrode reaction is highly active, so expensive negative electrode catalyst
is not needed and thus the price is low. In terms of high energy density of metal-air
battery, Table 6.1 lists the comparison of actual performance parameters between
two metal-air batteries and other kinds of vehicle power batteries.
Although the metal-air battery has obvious advantages, due to the high activity of
the metal negative electrode, there are also some negative effects, for example, the
self-discharge of metal contact electrolyte and the adhesion of discharge products
on the metal surface reduce the discharge efficiency of the negative electrode, which
225
thickness of the catalyst layer is 50 μm and the geometric area of the electrode is
0.2475 cm
2 (A geo = 0.2475 cm
2 ), then the real area of the catalyst layer (A real ) is the
sum of the geometric area of the electrode (A geo ) and the side area of the catalyst
layer (A side ). At present, it is impossible to measure the thickness of catalyst thin
layer accurately when measuring oxygen reduction with rotating disk electrode or
ring disk electrode. When calculating the limiting current density of catalyst oxygen
reduction reaction, it is still calculated according to the geometric area of electrode.
Thus, the calculated limiting current density is greater than 6 mA cm
−2 (as shown
in Eqs. 6.2.3–6.7, 6.2.3–6.8 and 6.2.3–6.9).
A real = A geo + A side = 0.2475cm
2
+ 0.005 ∗ 3.14 ∗ 0.56 cm
2
= 0.2563 cm
2
(6.10)
i d = 0.62nF D
2/3
0 ω
1/2 v
−1/6 C 0 A real = 6 ∗ 0.2563 = 1.538 mA
(6.11)
i d / A geo = 1.538 mA / 0.2475 cm
2
= 6.214 mA cm
−2
(6.12)
6.2 Application in Metal-Air Battery
6.2.1 Overview of Metal-Air Batteries
The so-called metal-air battery refers to a kind of “semi-fuel cell” with the characteristics of both primary cell and fuel cell. The negative electrode of the battery is
metal, the positive electrode of the battery is air electrode, and electrolyte is between
the positive and negative electrodes of the battery [37–39].
Electrolytes can be divided into three types according to the reaction characteristics of metal negative electrodes: aqueous, nonaqueous and aqueous–nonaqueous
mixed. Metal negative electrode of metal-air battery acts like fuel in fuel cell. Metalair battery is also called metal fuel cell. The biggest difference with primary battery
is that the positive active material of metal-air battery is air, the air electrode only
accounts for a small part of the battery volume, and the vacant position can carry a
large amount of active negative metal, so that the metal-air battery has a large energy
density. The biggest difference with fuel cells is that the metal fuel is built-in and the
negative electrode reaction is highly active, so expensive negative electrode catalyst
is not needed and thus the price is low. In terms of high energy density of metal-air
battery, Table 6.1 lists the comparison of actual performance parameters between
two metal-air batteries and other kinds of vehicle power batteries.
Although the metal-air battery has obvious advantages, due to the high activity of
the metal negative electrode, there are also some negative effects, for example, the
self-discharge of metal contact electrolyte and the adhesion of discharge products
on the metal surface reduce the discharge efficiency of the negative electrode, which