Porous carbon nanofibers confined NiFe alloy nanoparticles as efficient bifunctional electrocatalysts for Zn-air batteries

Zn-air batteries (ZABs) present attractive applications for next-generation sustainable energy storage owing to their low cost and intrinsic safety; however, the power density and durability of ZABs are often limited by the poor ion/mass transfer at triple-interfaces. Here, we propose efficient structural engineering to significantly promote the O-2 adsorption/transfer and OH- diffusion. By confining NiFe alloy nanoparticles into porous carbon nanofibers, the as-designed bifunctional catalysts (H-NiFe/CNF) feature abundant hierarchical pores and a high specific surface area. The finite element method and oxygen adsorption-desorption measurement convincingly confirm that this ingenious structural design dramatically enlarges the adsorption capacity, diffusion efficiency and transport scale of OH-/oxygen. These charming characteristics allow the H-NiFe/CNF to exhibit remarkable bifunctional activity, delivering an indicator delta E of 0.67 V, which is superior to most previous reports and noble -metal-based Pt/C+IrO2 benchmark. Accordingly, long-term stability (over 800 cycles at 5 mA cm(-2)) and excellent rate performances are achieved in liquid ZABs. Correspondingly, the flexible ZABs also exhibit high power density and long-cycling durability. This work highlights ion/mass transfer regulation to design bifunc-tional oxygen electrocatalysis for the metal-air battery.