Single-atom catalyst with a hollow rod/plate-like structure for enhanced oxygen reduction reaction performance in zinc–air batteries†

Abstract

The development of efficient and stable catalysts is critical for various energy and environmental applications. In the present study, transition metal single-atom catalysts (TM SACs) with hollow shell morphology were prepared. Our approach of self-templating with in situ polymerization involves the precise encapsulation of transition metal single-atoms within a nitrogen-doped carbon shell, forming a robust hollow architecture. The developed synthesis strategy is applicable for the synthesis of a variety of transition metal single-atom catalysts such as Fe–N–C SACs, Co–N–C SACs, Mn–N–C SACs, and Ni–N–C SACs. Among these, Fe–N–C SACs showed the best ORR activity in both acidic and basic media, with a half wave potential (E_1/2) of 0.81 V and 0.91 V and a limiting current density (J_L) of 5.96 mA cm⁻² and 5.12 mA cm⁻², respectively, which are higher than those of the state-of-the-art 20% Pt/C catalyst. Theoretical calculation illustrated that the Fe–N–C SAC exhibits the lowest d-band center (−2.364 eV), indicating that adsorption of oxygen-containing intermediates on the catalyst is easier, further validating its excellent catalytic properties compared with Co-, Mn- and Ni-based catalysts. The high ORR performance was further confirmed by assembling a homemade zinc–air battery (ZAB) using the Fe–N–C SAC as a cathode, showing a high power density of 185 mW cm⁻². The enhanced performance is accredited to the novel hollow design, which provides a favorable environment for active sites, prevents agglomeration of metal atoms, and ensures high electron conductivity. This work not only introduces a novel approach for designing advanced single-atom catalysts but also confirms their possible applications in energy transformation and storage devices.