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

Abstract

The critical challenge restricting the large-scale commercialization of metal–air batteries is the delayed reaction rate of the cathodic oxygen reduction reaction (ORR). Herein, we introduced Hf atoms with a high ligand field into a Fe/NC system through a self-sacrificing template strategy to modulate its electronic configuration, thereby optimizing the binding energy of oxygen-bearing intermediates and boosting the activity and stability of the ORR. In addition, the doping of Hf atoms promoted the in situ growth of NCNTs, thereby facilitating electron transfer during the electrocatalytic process. Therefore, the Hf–Fe/NC electrocatalyst exhibited excellent ORR performance in contrast to those utilizing the Pt/C benchmark, and the constructed rechargeable Zn–air and Mg–air batteries exhibited excellent power densities of 160 and 48 mW cm⁻² and outstanding specific capacities of 811 mA h g_Zn⁻¹ and 1055 mA h g_Mg⁻¹, respectively. This study underscores the pivotal role of high-ligand-field Hf doping in significantly facilitating the ORR performance, accelerating the application of non-precious metal electrocatalysts within metal–air batteries.