Noble metal catalysts for metal-air batteries: From nano-level to atom-level

Benefiting from the ultra-high specific energy that is even comparable to gasoline, metal-air batteries (MABs) showcase great promising practical prospects in next-generation battery technologies that beyond the commercial Li-ion batteries. Even though the advances witnessed in MABs in the last decades, there are still numerous critical scientific challenges that need to be solved for their future practical applications. Especially, ascribed to the sluggish reaction kinetics and high overpotentials of air cathodes, the performances of MABs are less than ideal, which also makes its industrialization prospect unclear. Noble metal-based catalysts often show the superior catalytic activity in MABs, but the corresponding systematic review is still not given. Our review mainly focuses on the relationship between the MABs performances and the composite and structure of the noble metal catalysts regarding their size from nano to atom levels. In this review, we first introduced the synthesis strategies of the noble metal-based nano-catalysts followed up by discussing the influences of the size, morphology, and support of noble metal-based catalysts as well as their applications in a variety of MABs. In the following sections, the main advanced characterization techniques for single atom catalysts (SACs) and the roles and recent progress of the noble metal-based SACs were also discussed in detail. Finally, we provided personal outlook and perspectives towards the challenges and future development of MABs and noble metal-based catalysts.