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

Abstract

Highly efficient and stable and low-cost catalysts equipped with a 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 a 3D network structure, including heterojunction FeCu/FeF₃ active nanoparticles and enriched N, F co-doping (FeCu/FeF₃@HPCNFs), are prepared for the oxygen reduction/evolution reaction (ORR/OER). The hierarchically porous structure inside the nanofibers combined 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 heteroatom co-doping can reduce the charge transport resistance and accelerate the catalytic reaction rate. Thus, the FeCu/FeF₃@HPCNFs display exceedingly good electrocatalytic performance for ORR (E_ORR,1/2 = 0.87 V vs. RHE) and OER (η_OER,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 an outstanding maximum power density and excellent long-term cycling stability. In addition, the theoretical analysis reveals that the FeCu/FeF₃@HPCNF electrocatalyst can reasonably adjust the electron distribution, effectively lower the reaction barrier of the intermediate and greatly reduce the OER/ORR overpotential. All in all, this work will open new avenues for the facile construction of highly active, structurally stable and cost-effective bi-functional catalysts for ZABs.