6 Application of Oxygen Reduction Catalysts
247
observing the electrode material after discharge, it was found that more products
were deposited on the edges of graphene, because the carbon atoms on the edges
have higher oxygen reduction activity due to the presence of unsaturated bonds. They
also studied the performance of doped graphene, and found that after doping nitrogen,
the number of defect sites and surface functional groups in graphene increased, which
showed a certain electrocatalytic activity for the electrode reaction, further improving
the performance of the battery (Fig. 6.14).
Xiao et al. used a surfactant to functionalize graphene, and then built it into a threedimensional electrode with different pores. It was found that the mass transfer in the
electrode was accelerated, and the electrochemically active area was also greatly
increased, as shown in Fig. 6.15.
6.4.2 Metal Oxide Electrocatalyst
Manganese oxide is the most studied electrocatalyst material in the field of lithiumair batteries. Bruce et al. systematically compared manganese oxides with different
morphologies, sizes, compositions, and crystal forms, and found that nanowires
showed the best performance (Fig. 6.16).
In addition, a variety of other metal oxides such as Fe 2 O 3 , Fe 3 O 4 , Ni O, Cu O
and Co 3 O 4 are also used as electrocatalyst materials for lithium-air batteries. Because
they have different catalytic activities, the batteries exhibit different charge and
discharge properties. Among them, the Fe 2 O 3 material shows the highest discharge
capacity, and the Fe 3 O 4 and Cu O materials show a relatively high capacity retention
rate, and the Co 3 O 4 material has good performance on discharge capacity and cycle
life. Wen et al. used an ammonia-induced evaporation growth method to synthesize
directionally grown Co 3 O 4 nanorods on the surface of nickel foam and directly used
them as electrodes for lithium-air batteries (Fig. 6.17), which can be used both as
an electrode for discharge products to be deposited and an electrocatalyst which
promoted the electrode reaction.
6.4.3 Precious Metal Electrocatalyst
Shao-Horn et al. reported for the first time the use of PtAu/C electrocatalysts to show
good “dual-function” catalytic activity in lithium-air batteries, that is, the electrocatalyst is active for both oxygen reduction and oxygen evolution, thereby enabling
battery energy efficiency is greatly improved. As shown in Fig. 6.18, the use of alloy
electrocatalysts reduces the polarization voltage, especially the charging voltage is
reduced by about 900 mV compared to activated carbon.
Further research by the Shao-Horn group showed that among a variety of precious
metal electrocatalysts, palladium showed the highest activity for oxygen reduction
catalysis, and correspondingly it had the lowest overpotential during the discharge
247
observing the electrode material after discharge, it was found that more products
were deposited on the edges of graphene, because the carbon atoms on the edges
have higher oxygen reduction activity due to the presence of unsaturated bonds. They
also studied the performance of doped graphene, and found that after doping nitrogen,
the number of defect sites and surface functional groups in graphene increased, which
showed a certain electrocatalytic activity for the electrode reaction, further improving
the performance of the battery (Fig. 6.14).
Xiao et al. used a surfactant to functionalize graphene, and then built it into a threedimensional electrode with different pores. It was found that the mass transfer in the
electrode was accelerated, and the electrochemically active area was also greatly
increased, as shown in Fig. 6.15.
6.4.2 Metal Oxide Electrocatalyst
Manganese oxide is the most studied electrocatalyst material in the field of lithiumair batteries. Bruce et al. systematically compared manganese oxides with different
morphologies, sizes, compositions, and crystal forms, and found that nanowires
showed the best performance (Fig. 6.16).
In addition, a variety of other metal oxides such as Fe 2 O 3 , Fe 3 O 4 , Ni O, Cu O
and Co 3 O 4 are also used as electrocatalyst materials for lithium-air batteries. Because
they have different catalytic activities, the batteries exhibit different charge and
discharge properties. Among them, the Fe 2 O 3 material shows the highest discharge
capacity, and the Fe 3 O 4 and Cu O materials show a relatively high capacity retention
rate, and the Co 3 O 4 material has good performance on discharge capacity and cycle
life. Wen et al. used an ammonia-induced evaporation growth method to synthesize
directionally grown Co 3 O 4 nanorods on the surface of nickel foam and directly used
them as electrodes for lithium-air batteries (Fig. 6.17), which can be used both as
an electrode for discharge products to be deposited and an electrocatalyst which
promoted the electrode reaction.
6.4.3 Precious Metal Electrocatalyst
Shao-Horn et al. reported for the first time the use of PtAu/C electrocatalysts to show
good “dual-function” catalytic activity in lithium-air batteries, that is, the electrocatalyst is active for both oxygen reduction and oxygen evolution, thereby enabling
battery energy efficiency is greatly improved. As shown in Fig. 6.18, the use of alloy
electrocatalysts reduces the polarization voltage, especially the charging voltage is
reduced by about 900 mV compared to activated carbon.
Further research by the Shao-Horn group showed that among a variety of precious
metal electrocatalysts, palladium showed the highest activity for oxygen reduction
catalysis, and correspondingly it had the lowest overpotential during the discharge