Selection of oxygen reduction catalysts for rechargeable lithium–air batteries—Metal or oxide?

Carbon-supported Pd and PdO nanocatalysts were synthesised using either chemical reduction or thermal synthesis procedures and were used as model metal and oxide catalysts for oxygen reduction in rechargeable lithium–air batteries. The Pd metal catalyst showed excellent initial performance, e.g. a discharge capacity of 855 mAh (g solids)−1. However, the PdO catalyst displayed superior capacity retention to the Pd catalyst, producing a discharge capacity of 336 mAh (g solids)−1 after 10 cycles, i.e. the capacity retention was 6% per cycle. The activity and stability of Pd metal and oxide catalysts were found to be closely related to their intrinsic catalytic properties and structural changes during charge/discharge cycles in Li–air batteries. The implication of such a difference is discussed. Model Pd/C and PdO/C catalysts were compared with other widely used carbon-supported metal and oxide catalysts, including Pt/C, Ru/C, RuO2/C and MnO2/C.

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► Carbon-supported Pd and PdO as model electrocatalysts.
► Catalysts for oxygen reduction in rechargeable Li–air batteries.
► Model catalysts compare with Pt/C, Ru/C, RuO2/C and MnO2/C.
► Oxides are better cathode catalysts than their metal counterparts.
► Changes in property and structure affect the catalyst activity and stability.