76
C. Juhong et al.
3.6.1 Overview of Commonly Used Electrochemical
Measurements of Specific Surface Area
The electrochemical methods currently used to measure the electrochemical specific
surface area of catalysts having a high specific surface area include measuring the
integrated charge of the hydrogen desorption zone, the desorption of the saturated
adsorbed CO, and the desorption of the underlying potential of the single layer of
Cu.
Measuring the desorption amount of saturated adsorbed CO The basic principle
of determining the active area is to use CO as a detection molecule, which can occupy
all active sites of electrocatalytic activity of the catalyst, and obtain the active area of
the catalyst by monitoring the change of the oxidative desorption electric quantity.
For organic electrochemical reactions, CO is very easy to achieve CO adsorption
because it is an intermediate substance for many reactions. As early as 1962, Gilman
began to study the adsorption behavior of CO on the electrode [22], and found that
the adsorption of CO is controlled by diffusion and there are at least two bonding
states on the polycrystalline platinum electrode. Adsorption of CO can be used to
measure the active area of a metal or alloy, but the bonding mode of adsorbed CO is
very complicated, such as linear adsorption, bridge adsorption and flat adsorption,
and the bonding mode is closely related to metal surface state and defect density. At
lower potentials, CO adsorbs strongly on the surface of Pt and other metals. When
the adsorption of CO on the surface of the electrode reaches saturated adsorption,
it is electrochemically oxidatively desorbed. In this process, oxidative desorption is
complete with a single layer of CO. The amount of active point exchanged between
the molecule and the electrode is calculated. This part of the oxidative desorption is
usually included in the cyclic voltammetry curve, the amount of electricity required
for oxidation of the CO, the charge of the electric double layer, the oxidation of the
active material, and the oxidation of the remaining adsorbed ions. In the calculation,
it is necessary to deduct the electric charge of the electric double layer, the oxidation
of the active material, and the oxidation amount of the remaining adsorbed ions,
and extract the desorption amount purely for CO oxidation. The electric charge
deduction of the electric double layer is generally considered to be the same as that
of the electric double layer in the CO oxidation desorption region and the electric
double layer region, thereby simplifying the calculation. A more rigorous subtraction
method can be found in the literature 23, which proposes two CO double-layer electric
charge deduction models, which respectively compare or exclude the influence of
the electric quantity caused by the Pt(111) surface special adsorption state on the
coverage calculation. The deduction of the oxidative charge of the active material
and the remaining adsorbed ions are complicated, which also limits the application
of CO in determining the active area. In addition to the complex background current
subtraction, the saturated adsorption state of CO is difficult to determine, and there
is also a CO coverage problem, such as incomplete coverage or lamination coverage,
and measurement results may have large errors. It is generally believed that the
C. Juhong et al.
3.6.1 Overview of Commonly Used Electrochemical
Measurements of Specific Surface Area
The electrochemical methods currently used to measure the electrochemical specific
surface area of catalysts having a high specific surface area include measuring the
integrated charge of the hydrogen desorption zone, the desorption of the saturated
adsorbed CO, and the desorption of the underlying potential of the single layer of
Cu.
Measuring the desorption amount of saturated adsorbed CO The basic principle
of determining the active area is to use CO as a detection molecule, which can occupy
all active sites of electrocatalytic activity of the catalyst, and obtain the active area of
the catalyst by monitoring the change of the oxidative desorption electric quantity.
For organic electrochemical reactions, CO is very easy to achieve CO adsorption
because it is an intermediate substance for many reactions. As early as 1962, Gilman
began to study the adsorption behavior of CO on the electrode [22], and found that
the adsorption of CO is controlled by diffusion and there are at least two bonding
states on the polycrystalline platinum electrode. Adsorption of CO can be used to
measure the active area of a metal or alloy, but the bonding mode of adsorbed CO is
very complicated, such as linear adsorption, bridge adsorption and flat adsorption,
and the bonding mode is closely related to metal surface state and defect density. At
lower potentials, CO adsorbs strongly on the surface of Pt and other metals. When
the adsorption of CO on the surface of the electrode reaches saturated adsorption,
it is electrochemically oxidatively desorbed. In this process, oxidative desorption is
complete with a single layer of CO. The amount of active point exchanged between
the molecule and the electrode is calculated. This part of the oxidative desorption is
usually included in the cyclic voltammetry curve, the amount of electricity required
for oxidation of the CO, the charge of the electric double layer, the oxidation of the
active material, and the oxidation of the remaining adsorbed ions. In the calculation,
it is necessary to deduct the electric charge of the electric double layer, the oxidation
of the active material, and the oxidation amount of the remaining adsorbed ions,
and extract the desorption amount purely for CO oxidation. The electric charge
deduction of the electric double layer is generally considered to be the same as that
of the electric double layer in the CO oxidation desorption region and the electric
double layer region, thereby simplifying the calculation. A more rigorous subtraction
method can be found in the literature 23, which proposes two CO double-layer electric
charge deduction models, which respectively compare or exclude the influence of
the electric quantity caused by the Pt(111) surface special adsorption state on the
coverage calculation. The deduction of the oxidative charge of the active material
and the remaining adsorbed ions are complicated, which also limits the application
of CO in determining the active area. In addition to the complex background current
subtraction, the saturated adsorption state of CO is difficult to determine, and there
is also a CO coverage problem, such as incomplete coverage or lamination coverage,
and measurement results may have large errors. It is generally believed that the