High-Density Atomic Fe-N-4/C in Tubular, Biomass-Derived, Nitrogen-Rich Porous Carbon as Air-Electrodes for Flexible Zn-Air Batteries

Developing low-cost single-atom catalysts (SACs) with high-density active sites for oxygen reduction/evolution reactions (ORR/OER) are desirable to promote the performance and application of metal-air batteries. Herein, the Fe nanoparticles are precisely regulated to Fe single atoms supported on the waste biomass corn silk (CS) based porous carbon for ORR and OER. The distinct hierarchical porous structure and hollow tube morphology are critical for boosting ORR/OER performance through exposing more accessible active sites, providing facile electron conductivity, and facilitating the mass transfer of reactant. Moreover, the enhanced intrinsic activity is mainly ascribed to the high Fe single-atom (4.3 wt.%) loading content in the as-synthesized catalyst.Moreover, the ultra-high N doping (10 wt.%) can compensate the insufficient OER performance of conventional Fe-N-C catalysts. When as-prepared catalysts are assembled as air-electrodes in flexible Zn-air batteries, they perform a high peak power density of 101 mW cm(-2), a stable discharge-charge voltage gap of 0.73 V for >44 h, which shows a great potential for Zinc-air battery. This work provides an avenue to transform the renewable low-cost biomass materials into bifunctional electrocatalysts with high-density single-atom active sites and hierarchical porous structure.