In-situ formation of isolated iron sites coordinated on nitrogen-doped carbon coated carbon cloth as self-supporting electrode for flexible aluminum-air battery

The demand for flexible energy storage systems with low-cost and high durability increases rapidly with the development of flexible electronics. Wherein, flexible metal-air batteries have been considered as potential candidates to meet the requirements of future power sources. However, the oxygen reduction reaction (ORR) performance at the air cathode is often restricted by inherent electrocatalytic activity and electrode configuration. To solve these problems, herein a novel approach utilizing the gas diffusion and subsequent pyrolysis process based on ferrocene and zinc-based metal–organic framework (Zn-MOF) is proposed to prepare nitrogen-doped carbon flakes modified with iron single atoms (Fe-SA) on carbon cloth (CC) as a self-supporting electrode (Fe-SA-NC@CC) for the aluminum-air battery. Benefitting from the excellent cooperation between the inherent ORR activity of Fe-SA and the rapid ion/electron transport of nitrogen-doped carbon flakes on CC, the resulting Fe-SA-NC@CC displays high ORR activity along with good flexibility and high durability. In a hydrogel-based solid-state aluminum-air battery, Fe-SA-NC@CC cathode reveals an impressive open-circuit voltage of 2.1 V even at a bending state, and it also shows a stable discharge voltage of ≈1.5 V over 8 h at 1 mA cm⁻². This study offers a promising method to construct self-supporting electrodes modified with single atoms for high-performance metal-air batteries.