158
6 Nanomaterials for Batteries
lead, and cadmium have a high hydrogen evolution overpotential to achieve a good
corrosion inhibition effect. However, these metals with toxicity are harmful to the
environment and the human body, it is limited to use.
6.4.3 Cathode Component and Its Influence
The air electrode reaction is performed at the three-phase interface of the gas–solid–
liquid. Because the diffusion rate of the sample in the aqueous solution is small and the
current density is small when the two-phase electrode is used, the three-phase electrode is used (Girishkumar 2010). The structure of the three-phase electrode consists
of an active layer (hydrophilic activation layer), a hydrophobic layer (hydrophobic
gas supply layer or waterproof gas-permeable layer), a conductive network (nickel
mesh or nickel-copper mesh), and whether the interior of the electrode can be formed
as much as possible. The effective three-phase interface will affect the utilization of
the catalyst and the mass transfer process of the electrode.
6.4.3.1 Catalyst
The development of metal-air batteries is mainly the continuous renewal of oxygen
electrode catalysts. In order to reduce the electrochemical polarization in the positive
electrode reaction process, people have conducted extensive research on the electrocatalysts for oxidation–reduction reactions. The earliest carbon used in redox electrocatalysts was its catalytic activity, but its catalytic activity is currently limited to
platinum and its alloys, silver, metal chelates, metal oxides (e.g., manganese oxides,
calcium titanium), mineral oxides, etc. several series (Cheng and Chen 2012).
(1) Precious metal catalysts. Platinum and silver are the mostly used catalysts,
although their catalytic performance is relatively high, few people use these
precious metals because of expensive price.
(2) Metal macrocyclic compound catalysts. Organometallic macrocycles have good
catalytic activity for oxygen reduction, especially when they are adsorbed on
large surface area carbons, the stability and catalytic activity of organometallic
macrocycles can be strikingly improved by heat treatment. Therefore, it is
expected to replace the noble metal oxygen reduction catalyst. Common
methods for synthesizing metal macrocyclic compounds include thermal
decomposition and precursor preparation. However, the heat treatment process
leads to the reaction of the metal macrocyclic compound with the carbon matrix,
and the catalyst prepared by the precursor method has poor activity, so there are
also some problems in the application.
(3) Perovskite-type oxide catalysts. Perovskite-type oxides not only have high
catalytic activity for the reduction and precipitation of oxygen, but also are
inexpensive. Therefore, Perovskite-type oxides are the promising materials
6 Nanomaterials for Batteries
lead, and cadmium have a high hydrogen evolution overpotential to achieve a good
corrosion inhibition effect. However, these metals with toxicity are harmful to the
environment and the human body, it is limited to use.
6.4.3 Cathode Component and Its Influence
The air electrode reaction is performed at the three-phase interface of the gas–solid–
liquid. Because the diffusion rate of the sample in the aqueous solution is small and the
current density is small when the two-phase electrode is used, the three-phase electrode is used (Girishkumar 2010). The structure of the three-phase electrode consists
of an active layer (hydrophilic activation layer), a hydrophobic layer (hydrophobic
gas supply layer or waterproof gas-permeable layer), a conductive network (nickel
mesh or nickel-copper mesh), and whether the interior of the electrode can be formed
as much as possible. The effective three-phase interface will affect the utilization of
the catalyst and the mass transfer process of the electrode.
6.4.3.1 Catalyst
The development of metal-air batteries is mainly the continuous renewal of oxygen
electrode catalysts. In order to reduce the electrochemical polarization in the positive
electrode reaction process, people have conducted extensive research on the electrocatalysts for oxidation–reduction reactions. The earliest carbon used in redox electrocatalysts was its catalytic activity, but its catalytic activity is currently limited to
platinum and its alloys, silver, metal chelates, metal oxides (e.g., manganese oxides,
calcium titanium), mineral oxides, etc. several series (Cheng and Chen 2012).
(1) Precious metal catalysts. Platinum and silver are the mostly used catalysts,
although their catalytic performance is relatively high, few people use these
precious metals because of expensive price.
(2) Metal macrocyclic compound catalysts. Organometallic macrocycles have good
catalytic activity for oxygen reduction, especially when they are adsorbed on
large surface area carbons, the stability and catalytic activity of organometallic
macrocycles can be strikingly improved by heat treatment. Therefore, it is
expected to replace the noble metal oxygen reduction catalyst. Common
methods for synthesizing metal macrocyclic compounds include thermal
decomposition and precursor preparation. However, the heat treatment process
leads to the reaction of the metal macrocyclic compound with the carbon matrix,
and the catalyst prepared by the precursor method has poor activity, so there are
also some problems in the application.
(3) Perovskite-type oxide catalysts. Perovskite-type oxides not only have high
catalytic activity for the reduction and precipitation of oxygen, but also are
inexpensive. Therefore, Perovskite-type oxides are the promising materials