Electronic Modulation of a Polymerized Iron-Phthalocyanine Catalyst via Ligand Engineering toward the Oxygen Reduction Reaction for Aluminum-Air Batteries

Aluminum-air batteries (AABs) are considered an advanced energy conversion system. However, the development of AABs is severely limited by slow kinetics of the oxygen reduction reaction (ORR) occurring at air cathodes. Although iron phthalocyanine (FePc) is considered a widely used ORR catalyst, rationally designing efficient and stable FePc-based electrocatalysts to replace commercial Pt/C is extremely challenging. Herein, ligand engineering is presented to achieve the electronic regulation of a polymerized FePc catalyst. Functionalized FePc-based catalysts were constructed based on 1,2,4,5-tetracyanobenzene (TCNB), 1,2-dicyanobenzene (1,2-DCB), and pyromellitic dianhydride (PMDA) as ligands. Benefiting from the conjugated polymer network and highly dispersed FeN_x sites, the FePc-TCNB catalyst demonstrates excellent ORR activity and durability, and the assembled Al-air battery delivers approved battery performance. Theoretical calculations further confirm the enhanced charge polarization and electron redistribution around Fe centers, which optimize the ORR process by decreasing the energy barrier and the adsorption energy of intermediates. This study develops a strategy for precise design of the FeN_x structure including the modulated microenvironment and electronic structure at the molecular level and also holds great promise for various applications of electrocatalysts and batteries.