18
Z. Zhao and P. K. Shen
the intermediate product. So from the middle product ratio of the reaction and the
influencing factors, we know that they are methods of continuous two-electron reactions. Although there have been many studies on the mechanism of oxygen reduction,
and many convincing theories have been proposed, there are still many details on
the main reaction pathways for oxygen reduction which are not clear enough. The
oxygen reduction reaction produces a small amount of H 2 O 2 on the electrocatalysts single-crystal Pt and Pt particle for the outside H upd (hydrogen under potential
deposition) potential range, and this is evidence that the four-electron reaction is
considered to be the main reaction pathway for oxygen reduction. Some theories
suggest that the dissociated oxygen is adsorbed on the Pt electrode, and then the
adsorbed oxygen atoms are directly reduced. While some others believe that this
reaction process must undergo two-step continuous two-electron reaction process.
At the same time, whether the intermediate product H 2 O 2 during the oxygen reduction reaction produced by electrochemical reduction or chemical adsorption is also
inconclusive. Therefore, the control reaction theory of oxygen reduction reaction has
been in dispute. One theory that is currently widely accepted is that the process in
which O 2 first acquires electrons is a controlled reaction of the oxygen reduction reaction. However, there are many other theories that hold different views. The control
reaction is to destroy the O–O double bond by the double-site mechanism, or the
process of O 2 initial adsorption on the surface of the electrocatalyst, or the process of
desorbing O or OH from the surface of the electrocatalyst. Among them, Wang et al.
believe that OH ads desorption in the potential interval of OH ads adsorption is a control
step. While in the interval where Pt has no product adsorption, O 2 acquired electrons
is a control step. These theories all indicate that the multielectron oxygen reduction
is a complex multistep reaction, and there are many reaction paths depending on the
morphology of the electrode and the difference of electrode potential.
Studying the mechanism of the two-electron reaction need first considers the
formation and detection of H 2 O 2 products. At present, rotating ring plate electrode
and rotating disk electrode for detecting H 2 O 2 are commonly used. The third chapter
will introduce the oxygen reduction research technology in detail, which will be
briefly introduced here.
Usually, the current on the planar electrode is not uniform and the mass transfer rate
in the aqueous solution is also relatively small. Which these bring many problems
to electrochemical manufacture and electrochemical theoretical research. Uneven
current density distribution in electrochemical devices means that the production
potential of each part of the electrode surface cannot be fully utilized and may cause
uneven distribution of reaction products. When the electrode reaction is studied in
the laboratory, this means that the polarization of electrode surfaces is different
throughout, making data processing complicated. The most common is the rotating
electrode. The mathematical processing of the liquid phase mass transfer kinetics on
the surface of the rotating electrode is relatively simple, and the uniform current distribution on the electrode surface is the basic experimental method in electrochemical
research.
The electrode is a disk electrode and a ring disk electrode that rotates around
an axis perpendicular to the disk surface through its center. As shown in Fig. 2.7,
Z. Zhao and P. K. Shen
the intermediate product. So from the middle product ratio of the reaction and the
influencing factors, we know that they are methods of continuous two-electron reactions. Although there have been many studies on the mechanism of oxygen reduction,
and many convincing theories have been proposed, there are still many details on
the main reaction pathways for oxygen reduction which are not clear enough. The
oxygen reduction reaction produces a small amount of H 2 O 2 on the electrocatalysts single-crystal Pt and Pt particle for the outside H upd (hydrogen under potential
deposition) potential range, and this is evidence that the four-electron reaction is
considered to be the main reaction pathway for oxygen reduction. Some theories
suggest that the dissociated oxygen is adsorbed on the Pt electrode, and then the
adsorbed oxygen atoms are directly reduced. While some others believe that this
reaction process must undergo two-step continuous two-electron reaction process.
At the same time, whether the intermediate product H 2 O 2 during the oxygen reduction reaction produced by electrochemical reduction or chemical adsorption is also
inconclusive. Therefore, the control reaction theory of oxygen reduction reaction has
been in dispute. One theory that is currently widely accepted is that the process in
which O 2 first acquires electrons is a controlled reaction of the oxygen reduction reaction. However, there are many other theories that hold different views. The control
reaction is to destroy the O–O double bond by the double-site mechanism, or the
process of O 2 initial adsorption on the surface of the electrocatalyst, or the process of
desorbing O or OH from the surface of the electrocatalyst. Among them, Wang et al.
believe that OH ads desorption in the potential interval of OH ads adsorption is a control
step. While in the interval where Pt has no product adsorption, O 2 acquired electrons
is a control step. These theories all indicate that the multielectron oxygen reduction
is a complex multistep reaction, and there are many reaction paths depending on the
morphology of the electrode and the difference of electrode potential.
Studying the mechanism of the two-electron reaction need first considers the
formation and detection of H 2 O 2 products. At present, rotating ring plate electrode
and rotating disk electrode for detecting H 2 O 2 are commonly used. The third chapter
will introduce the oxygen reduction research technology in detail, which will be
briefly introduced here.
Usually, the current on the planar electrode is not uniform and the mass transfer rate
in the aqueous solution is also relatively small. Which these bring many problems
to electrochemical manufacture and electrochemical theoretical research. Uneven
current density distribution in electrochemical devices means that the production
potential of each part of the electrode surface cannot be fully utilized and may cause
uneven distribution of reaction products. When the electrode reaction is studied in
the laboratory, this means that the polarization of electrode surfaces is different
throughout, making data processing complicated. The most common is the rotating
electrode. The mathematical processing of the liquid phase mass transfer kinetics on
the surface of the rotating electrode is relatively simple, and the uniform current distribution on the electrode surface is the basic experimental method in electrochemical
research.
The electrode is a disk electrode and a ring disk electrode that rotates around
an axis perpendicular to the disk surface through its center. As shown in Fig. 2.7,