Doping hafnium with a high ligand field to modulate the electronic structure of Fe/NC for achieving remarkable ORR activity in Zn–air and Mg–air batteries

Doping high-ligand-field Hf atoms can optimize the binding energy of oxygen-containing intermediates at Fe–N x sites. The Hf–Fe/NC electrocatalyst exhibited potential for practical applications in Zn–air and Mg–air batteries.