The paper provides an overview of transition metal macrocyclic (TMM) complex-based electrocatalysts used in ORRs in PEMFCs.
Performances of TMM catalysts, including both ORR activity rates and stabilities, are discussed.
The effects of different types and natures of metals, macrocyclic ligands, and so on are analyzed and reviewed.
Required improvements of TMM catalysts in ORR activity, stability and commercial viability are identified.
Potential research directions to overcome current challenges are suggested.