6 Application of Oxygen Reduction Catalysts
219
6.1.2 Half-Wave Potential (E 1/2 )
The half-wave potential of oxygen reduction is the potential corresponding to the
half of the limiting diffusion current. Half-wave potential is an important parameter
of oxygen reduction performance of catalyst material, which can be directly obtained
from oxygen reduction curve, and it is a direct reflection of electrocatalytic activity of
oxygen reduction catalyst. From catalyst (Pt catalysts, for example), the calculation
[formula (6.1) ~ (6.3)] of quality activity and specific activity can be seen that
different catalyst with moderate thickness (the limiting current of oxygen reduction
test will not change obviously due to the thickness of catalyst layer) and the same test
conditions (such as the same temperature, the same electrolyte solution, the same
speed and the same electrochemical scanning speed), when the quality of the catalyst
active substances (Pt) and specific surface area are constant, and oxygen reduction
limiting current phase is the same, the higher the half-wave potential of oxygen
reduction, the better the mass activity and specific activity of the catalyst at the same
potential.
i k = i d i/(i d − i)
(6.1)
i m (mA mg
−1
Pt ) =
i k (m A)
Pt Loading (mg)
(6.2)
i = n F D 0
a
0
O − a
s
O
δ
(6.3)
i k is the kinetic current, and i d is the limiting current; i is the measured current under
any potential; i m is the mass activity of catalyst; i s is the specific activity of catalyst;
Q H-adsorption is electricity of hydrogen adsorption, L Pt is Pt loading mass.
The half-wave potential is mainly dependent on the oxygen reduction catalyst
material, and it is also affected by the supporting electrolyte solution and the test
temperature. The catalyst material, supporting electrolyte and test temperature are
discussed.
It can be seen that the treatment of nanoporous pni alloy with ionic liquid
([MTBD][beti]) significantly improved the half-wave potential of oxygen reduction [about 0.4 V vs. (RHE)], mainly because the solubility and diffusion coefficient
of oxygen in ionic liquid ([MTBD][beti]] were significantly improved in perchloric
acid solution.
As shown in Fig. 6.1, the half-wave potential of oxygen reduction reaction
polarization curve of commercial Pt/C catalyst (Japan TKK, 47.6%Pt) in various
oxygen saturated electrolyte solutions (perchloric acid, sulfuric acid, nitric acid and
hydrochloric acid) is also different, commercial Pt/C catalysts with the same amount
showed the highest oxygen reduction half-wave potential in perchloric acid solution,
and the second is in solutions of nitric and sulfuric acid, while in hydrochloric acid
solution, the half-wave potential of oxygen reduction in catalyst oxygen reduction
219
6.1.2 Half-Wave Potential (E 1/2 )
The half-wave potential of oxygen reduction is the potential corresponding to the
half of the limiting diffusion current. Half-wave potential is an important parameter
of oxygen reduction performance of catalyst material, which can be directly obtained
from oxygen reduction curve, and it is a direct reflection of electrocatalytic activity of
oxygen reduction catalyst. From catalyst (Pt catalysts, for example), the calculation
[formula (6.1) ~ (6.3)] of quality activity and specific activity can be seen that
different catalyst with moderate thickness (the limiting current of oxygen reduction
test will not change obviously due to the thickness of catalyst layer) and the same test
conditions (such as the same temperature, the same electrolyte solution, the same
speed and the same electrochemical scanning speed), when the quality of the catalyst
active substances (Pt) and specific surface area are constant, and oxygen reduction
limiting current phase is the same, the higher the half-wave potential of oxygen
reduction, the better the mass activity and specific activity of the catalyst at the same
potential.
i k = i d i/(i d − i)
(6.1)
i m (mA mg
−1
Pt ) =
i k (m A)
Pt Loading (mg)
(6.2)
i = n F D 0
a
0
O − a
s
O
δ
(6.3)
i k is the kinetic current, and i d is the limiting current; i is the measured current under
any potential; i m is the mass activity of catalyst; i s is the specific activity of catalyst;
Q H-adsorption is electricity of hydrogen adsorption, L Pt is Pt loading mass.
The half-wave potential is mainly dependent on the oxygen reduction catalyst
material, and it is also affected by the supporting electrolyte solution and the test
temperature. The catalyst material, supporting electrolyte and test temperature are
discussed.
It can be seen that the treatment of nanoporous pni alloy with ionic liquid
([MTBD][beti]) significantly improved the half-wave potential of oxygen reduction [about 0.4 V vs. (RHE)], mainly because the solubility and diffusion coefficient
of oxygen in ionic liquid ([MTBD][beti]] were significantly improved in perchloric
acid solution.
As shown in Fig. 6.1, the half-wave potential of oxygen reduction reaction
polarization curve of commercial Pt/C catalyst (Japan TKK, 47.6%Pt) in various
oxygen saturated electrolyte solutions (perchloric acid, sulfuric acid, nitric acid and
hydrochloric acid) is also different, commercial Pt/C catalysts with the same amount
showed the highest oxygen reduction half-wave potential in perchloric acid solution,
and the second is in solutions of nitric and sulfuric acid, while in hydrochloric acid
solution, the half-wave potential of oxygen reduction in catalyst oxygen reduction