6 Application of Oxygen Reduction Catalysts
235
(3) Electrolyte for Aluminum-Air Battery
As mentioned earlier, the electrolyte of aluminum-air battery mainly includes alkaline
electrolyte and neutral electrolyte. The alkaline electrolyte is mainly NaOH or KOH
aqueous solution, and the neutral salt electrolyte is mainly NaCl or NH 4 Cl aqueous
solution. In order to solve the defects of hydrogen evolution corrosion of aluminum
negative electrode in alkaline electrolyte and slow discharge speed of aluminum
negative electrode in neutral electrolyte, additives that inhibit hydrogen evolution
corrosion of aluminum and can activate aluminum negative electrode are generally
added to electrolyte [53–55]. The main additives are: (1) Inorganic ions, such as Cl
− ,
F
− , SO 4
2− , SnO 3
2− , Bi
3+ , In
3+ and Ga
3+ , etc. Cl
− and F
− can activate the negative
electrode of aluminum. Bi
3+ , In
3+ and Ga
3+ plasma will be deposited on the surface
of aluminum cathode, which will destroy the anode passivation film. SnO 3
2− can
not only play the role of anode activation, but also be reduced to Sn, forming a
porous precipitate on the aluminum surface to inhibit hydrogen evolution corrosion
of the cathode, and Sn(OH) 2 generated by SnO 3
2− hydrolysis can be used as crystal
nucleus of precipitated colloidal Al(OH) 3 to improve the conductivity of electrolyte;
(2) Organic additives such as ethylenediaminetetraacetic acid can form coordination
ions with aluminum ions to inhibit the formation of colloidal Al(OH) 3 ; Citrate can
inhibit the hydrogen evolution corrosion of aluminum and the generation of Al(OH) 3 ,
while ethanol can reduce the corrosion of aluminum cathode surface. (3) Composite
additives, compared with pure inorganic ions or organic additives, the improvement
mechanism of composite additives on electrolyte performance is relatively complex,
and various influencing factors interact with each other, so further research is needed.
Some scholars compound K 2 MnO 4 with citrate and stannate as electrode additives,
which improves the utilization rate of aluminum cathode from 28.5 to 81.0%, and
reduces the corrosion current density from 123.8 mA/cm
2 to 17. 87 mA/cm
2 .
The Al(OH) 3 accumulated in the electrolyte will be supersaturated, making the
electrolyte pasty or even semisolid, resulting in a decrease in the conductivity of
the electrolyte. Common solutions include replacing electrolyte regularly, circulating electrolyte or adding seed crystal to the electrolyte to precipitate Al(OH) 3 . For
example, one of the purposes of adding SnO 3
2− to the electrolyte is to serve as seed
crystal. The corresponding battery design also includes precipitation and filtration
devices, etc.
Some scholars believe that acidic H 2 SO 4 electrolyte is better than NaCl (Cl
− ion
is easy to induce pitting corrosion of aluminum alloy). Strengthening the research
of electrolyte is expected to make the aluminum air battery have a wider application
prospect. Other scholars try to replace aqueous solution with organic polymer solid
electrolyte [56]. Research shows that solid polymer electrolyte (SPEM) is prepared
by mixing (poly vinyl alcohol: PVA) and (polyacrylic acid: PAA) at a ratio of 10: 7.5
and compounding alkaline solution. When the solid electrolyte is used in aluminumair battery, the utilization rate of aluminum cathode of aluminum-air battery can
reach 90%.
Since the aluminum-air battery is mainly a mechanical rechargeable battery using
aqueous electrolyte, the air electrode requirement is lower than that of the secondary
235
(3) Electrolyte for Aluminum-Air Battery
As mentioned earlier, the electrolyte of aluminum-air battery mainly includes alkaline
electrolyte and neutral electrolyte. The alkaline electrolyte is mainly NaOH or KOH
aqueous solution, and the neutral salt electrolyte is mainly NaCl or NH 4 Cl aqueous
solution. In order to solve the defects of hydrogen evolution corrosion of aluminum
negative electrode in alkaline electrolyte and slow discharge speed of aluminum
negative electrode in neutral electrolyte, additives that inhibit hydrogen evolution
corrosion of aluminum and can activate aluminum negative electrode are generally
added to electrolyte [53–55]. The main additives are: (1) Inorganic ions, such as Cl
− ,
F
− , SO 4
2− , SnO 3
2− , Bi
3+ , In
3+ and Ga
3+ , etc. Cl
− and F
− can activate the negative
electrode of aluminum. Bi
3+ , In
3+ and Ga
3+ plasma will be deposited on the surface
of aluminum cathode, which will destroy the anode passivation film. SnO 3
2− can
not only play the role of anode activation, but also be reduced to Sn, forming a
porous precipitate on the aluminum surface to inhibit hydrogen evolution corrosion
of the cathode, and Sn(OH) 2 generated by SnO 3
2− hydrolysis can be used as crystal
nucleus of precipitated colloidal Al(OH) 3 to improve the conductivity of electrolyte;
(2) Organic additives such as ethylenediaminetetraacetic acid can form coordination
ions with aluminum ions to inhibit the formation of colloidal Al(OH) 3 ; Citrate can
inhibit the hydrogen evolution corrosion of aluminum and the generation of Al(OH) 3 ,
while ethanol can reduce the corrosion of aluminum cathode surface. (3) Composite
additives, compared with pure inorganic ions or organic additives, the improvement
mechanism of composite additives on electrolyte performance is relatively complex,
and various influencing factors interact with each other, so further research is needed.
Some scholars compound K 2 MnO 4 with citrate and stannate as electrode additives,
which improves the utilization rate of aluminum cathode from 28.5 to 81.0%, and
reduces the corrosion current density from 123.8 mA/cm
2 to 17. 87 mA/cm
2 .
The Al(OH) 3 accumulated in the electrolyte will be supersaturated, making the
electrolyte pasty or even semisolid, resulting in a decrease in the conductivity of
the electrolyte. Common solutions include replacing electrolyte regularly, circulating electrolyte or adding seed crystal to the electrolyte to precipitate Al(OH) 3 . For
example, one of the purposes of adding SnO 3
2− to the electrolyte is to serve as seed
crystal. The corresponding battery design also includes precipitation and filtration
devices, etc.
Some scholars believe that acidic H 2 SO 4 electrolyte is better than NaCl (Cl
− ion
is easy to induce pitting corrosion of aluminum alloy). Strengthening the research
of electrolyte is expected to make the aluminum air battery have a wider application
prospect. Other scholars try to replace aqueous solution with organic polymer solid
electrolyte [56]. Research shows that solid polymer electrolyte (SPEM) is prepared
by mixing (poly vinyl alcohol: PVA) and (polyacrylic acid: PAA) at a ratio of 10: 7.5
and compounding alkaline solution. When the solid electrolyte is used in aluminumair battery, the utilization rate of aluminum cathode of aluminum-air battery can
reach 90%.
Since the aluminum-air battery is mainly a mechanical rechargeable battery using
aqueous electrolyte, the air electrode requirement is lower than that of the secondary