Facile construction of hierarchically porous carbon nanofibers modified by FeCu/FeF3 heterojunction for oxygen electrocatalysis in liquid and flexible Zn-air batteries

Highly efficiency, excellent stability and low-cost catalysts equipping with uniform distribution and enough active sites are rather important for zinc-air batteries (ZABs). In this study, inspired by hollow bubble structured carbon materials and heterostructure characteristics, the hierarchically porous carbon nanofibers with 3D network structure including heterojunction FeCu/FeF3 active nanoparticles and enriched N, F co-doping (FeCu/FeF3@HPCNFs) are prepared for oxygen reduction/evolution reaction (ORR/OER). The hierarchically porous structure inside the nanofibers combining with the hollow bubble structured carbon outside the nanofibers together can increase the specific surface area and carbon edge defects of the composite materials, thus effectively accelerating mass transfer at three-phase interfaces. Meanwhile, the heterojunction FeCu/FeF3 and unique heteroatoms co-doping can reduce charge transport resistance and accelerate catalytic reaction rate. Thus the FeCu/FeF3@HPCNFs display exceedingly good electrocatalytic performance for ORR (EORR, 1/2 = 0.87 V vs. RHE) and OER (ηOER, 10 = 377 mV at 10 mA cm−2). More importantly, both the aqueous rechargeable ZABs and flexible foldable solid-state ZABs assembled with the FeCu/FeF3@HPCNFs catalyst reveal a outstanding maximum power density and excellent long-term cycling stability. In addition, the theoretical analysis also reveals the FeCu/FeF3@HPCNFs electrocatalyst can reasonably adjust the electron distribution, effectively lower the reaction barrier of intermediate and greatly reduce OER/ORR overpotential. All in all, the work will open up a new avenue for facile construction of highly active, structurally stable and cost-effective bi-functional catalysts for ZABs.