N, F and S doped carbon nanofibers generated from electrospun polymerized ionic liquids for metal-free bifunctional oxygen electrocatalysis

Abstract

• Electrospinning was used to prepare multiple heteroatom-doped metal-free nanofibrous material derived from PAN and polymerized ionic liquids • A simple method of producing a free-standing air cathode with high surface area and micro-mesoporous structures • Remarkably enhanced bifunctional electrocatalytic performance and durability of the electrocatalyst • DFT calculations confirm the N, S, F tri-doping can effectively promote the catalytic performance of carbon nanofibers • Highly efficient rechargeable Zn-air batteries without organic binder and supportive materials been successfully assembled The rational development of promising oxygen electrocatalysts with remarkable electrocatalytic activity, high stability and low cost is highly important for wide-scale application of sustainable energy technologies. Here, a novel free-standing metal-free carbon-based bifunctional electrocatalyst (NFS-CNF) with uniform multiple heteroatom (N, F and S) doping and large specific surface area (1450.7 m 2 g −1 ), was firstly synthesized by direct pyrolysis of electrospun polyacrylonitrile (PAN)/polymerized ionic liquid (PIL) nanofibers. The as-prepared NFS-CNF presents superior oxygen catalytic performance as well as excellent durability, exhibiting a positive half-wave potential (0.91 V) for oxygen reduction reaction (ORR) and a low overpotential (380 mV at 10 mA cm −2 ) for oxygen evolution reaction (OER) in alkaline medium. Notably, the outstanding bifunctional ORR/OER activity (ΔE=0.70 V) endows remarkable Zn-air battery performance with a peak power density of 127.5 mW cm −2 , a high specific capacity of 826.4 mAh g Zn −1 (corresponding to an energy density of ~991 Wh kg Zn −1 ), a stable cyclability after 600 cycles at 10 mA cm −2 with a voltage gap increase as small as 0.1 V. Density functional theory (DFT) calculations confirm that the N, F, S tri-doping contributes to the improvement in the electrochemical properties of our material. Our work firstly experimentally demonstrates a simple pathway of combining PIL precursor and electrospinning technology to achieve multiple heteroatom doping in metal-free nanofibrous bifunctional oxygen electrocatalysts with greatly enhanced electrochemical activity and durability. Additionally, the realization of efficient rechargeable Zn-air batteries suggests the promising future of our NFS-CNF pieces as robust free-standing air cathodes in various sustainable energy applications.