Stabilizing iron single atoms with electrospun hollow carbon nanofibers as self-standing air-electrodes for long-time Zn - air batteries.

Developing iron-based single-atom catalysts (Fe SACs) with low cost, high activity and stability is vital for commercialising sustainable energy technologies. However, accurately controlling and identifying structure-activity relationships of Fe SACs remains a significant challenge. Herein, we report Fe/N co-doped carbon nanofiber membranes with highly exposed Fe-N sites (Fe/NCNFs), synthesized by electrospinning and pyrolysis. The three-dimensional (3D) hierarchical structure and atomically dispersed pyrrole-type Fe (III)-N active sites provide the as-prepared catalyst with a positive half-wave potential of 0.87 V and an ultralow Tafel slope of 53 mV dec. As an air cathode catalyst for liquid Zn - air batteries, it delivers a high open-circuit voltage (1.474 V), a large peak power density (190 mW cm) and a high durability of 2000 cycles at 5 mA cm. As a self-standing air cathode, the as-assembled solid-state Zn - air batteries also show stable cycling with a small discharge/charge voltage gap of 0.65 V, indicating great prospects for developing portable zinc - air batteries.