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Rational design of highly effective and low-cost oxygen reduction reaction (ORR) electrocatalysts to replace Pt-based catalysts is still a significant challenge for rechargeable zinc-air batteries. Hence, Fe, N co-doped one-dimensional carbon nanofibers with Fe 4 N species (Fe/N-CNFs) are synthesized through the electrospun technique combining with the "rapid calcination under vacuum" method. Benefitting from the one-dimensional structure obtained by the electrospun technique, the as-synthesized Fe/N-CNFs electrocatalyst with mesoporous exhibits a relatively large specific surface area of 624.12 m2 g−1. Notably, the intrinsic activity of Fe 4 N species as well as the large specific surface area can endow the resulting Fe/N-CNFs with a positive half-wave potential of 0.88 V compared with 20 wt% Pt/C (0.86 V) for ORR. The Fe/N-CNFs also exhibits better long-term stability than 20 wt% Pt/C. Furthermore, the rechargeable zinc-air battery constructed with Fe/N-CNFs as the cathode shows a high open-circuit voltage of 1.51 V, a peak power density of 135 mW cm−2 and an excellent cycle life for 55 h. The as-synthesized electrocatalyst is promising to replace the precious metal catalysts for rechargeable zinc-air batteries. Unlabelled Image • Fe, N co-doped carbon nanofibers (Fe/N-CNFs) with Fe 4 N species were synthesized. • The "rapid calcination under vacuum" was reported for the preparation of Fe/N-CNFs. • The one-dimensional structure of Fe/N-CNFs provides a large specific surface area. • The Fe/N-CNFs exhibits more excellent ORR activity than commercial 20 wt% Pt/C. • The Fe/N-CNFs endows zinc-air batteries with comparable performances to 20 wt% Pt/C. [ABSTRACT FROM AUTHOR]

Abstract Rechargeable Zn-air battery (ZAB) still relies on the precious metal-based catalysts, whose high cost, supply scarcity and inferior durability largely hamper the large-scale application of ZAB. Herein, a non-noble-metal catalyst towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is successfully constructed by carbonizing metal-organic frameworks (MOFs) functionalized electrospun nanofibers. The obtained bifunctional electrocatalyst shows good catalytic performance with comparable limiting diffusion current to Pt/C and comparable potential to RuO 2 , in particular, superior stability to both Pt/C and RuO 2 towards ORR and OER. In view of the efficient bifunctional catalyst activity for ORR and OER, the obtained catalyst in ZAB displays high charge/discharge performance and long cycling stability, demonstrating great potential in grid-scale energy storage. Graphical abstract A non-noble-metal catalyst towards both oxygen reduction reaction and oxygen evolution reaction is successfully constructed by carbonizing MOF functionalized electrospun nanofibers, which shows high charge/discharge performance, larger power density and long cycling stability in rechargeable Zn-air battery. Unlabelled Image Highlights • Co nanoparticles are homogenously encapsulated into N-doped carbon nanofibers. • The material is prepared by carbonizing MOF functionalized electrospun nanofibers. • This material could be used as a non-noble-metal bifunctional oxygen catalyst. • The catalyst in Zn-air battery displays high performance and long cycling stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The B, N, F tri-doped lignin-derived carbon nanofibers (BNF-LCFs) have been prepared by electrospinning and pyrolysis. • The specific synergistic effects between B, N and F dopants are essential for the super performance of the BNF-LCF catalyst. • The BNF-LCF catalyst exhibits superior ORR and OER bifunctional catalytic performance. • The BNF-LCF catalyst shows great potential in liquid/solid-state Zn-air batteries. The exploitation of cost-effective and high-efficiency bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is vital for the development of rechargeable metal-air batteries. Herein, B, N and F tri-doped lignin-based carbon porous nanofibers (BNF-LCFs) were prepared by electrospinning and pyrolysis without extra post-treatment using biomass lignin as carbon precursor, PVP as spinning additive, zinc borate as boron source, ammonium fluoride as fluorine source and partial nitrogen source. This method is simple, efficient, and environmentally friendly. Benefiting from the synergistic effect of B, N and F heteroatoms, large specific surface area and abundant defect sites, the BNF-LCF catalyst exhibits impressive bifunctional electrocatalytic performance towards ORR and OER with a small potential gap (ΔE) of 0.728 V. It outperforms the commercial Pt/C + RuO 2 and most recently-reported non-metal carbon-based electrocatalysts. The liquid Zn-air batteries (ZABs) assembled with BNF-LCFs present a high open circuit potential of 1.536 V, a large specific capacity of 791.5 mAh g−1 and satisfactory cycling stability, superior to Pt + RuO 2 -based ZABs. Furthermore, the solid-state ZABs assembled with BNF-LCFs not only deliver excellent electrochemical performance, but also exhibit admirable mechanical flexibility and cycling stability, indicating favorable application prospects in flexible and wearable electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient and stable bi-functional electrocatalyst is developed by a facile foaming-assisted electrospinning method. • FeCo alloy nanoparticles are uniformly embedded within N-doped mesoporous carbon nanofibers. • The FeCo@NCNF electrocatalyst exhibited excellent ORR and OER performances with a smaller potential gap (ΔE) of 0.749 V. • The as-constructed Zn-air battery exhibits a larger power density of 134.83 mW cm−2 and long-term cycling stability after 216 h tests. A low-cost, efficient and durable bi-functional electrocatalysts for bi-functional oxygen reduction/evolution reactions (ORR/OER) is vital for modern energy conversion devices. Here, we report the exploration of advanced OER/ORR bi-functional catalysts based on foaming-assisted electrospinning. The addition of foaming agent is beneficial to prevent the agglomeration of FeCo alloy nanoparticles decorated on the N-doped mesoporous carbon nanofibers (FeCo@NCNF). These rationally designed electrocatalysts exhibit an excellent bi-functional electrocatalytic activity with a low reversible overvoltage of 0.749 V. The as-constructed Zn-air battery delivers a power density of 134.83 mW cm−2 and long-term cycling stability with a slight increase of 0.02 V in potential gap over 216 h at 5 mA cm−2, surpassing to most bi-functional electrocatalysts ever reported. [ABSTRACT FROM AUTHOR]

• Few-layered MoS 2 nanosheets crosslinked with CNFs are fabricated. • Robust anodes are integrated with confined nanosize and expanded interlayers. • The contribution ratio of capacitive behavior is 72.7% at 1 mV s−1. A facile strategy has been designed for the synthesis of nanoflower-like MoS 2 /carbon nanofibers (CNFs) derived from bacterial cellulose. CNFs can well retain the fibrous structure with thickness of 21 nm. The formation of few-layered ultrathin MoS 2 nanosheets crosslinked with CNFs due to confined growth, leading to more active surface area. Among the varied compositions of MoS 2 /CNFs, the largest specific surface area is 35.1 m2 g−1. In addition, 3D porous architecture of CNFs can provide sufficient space to accommodate the volume change of MoS 2 during sodiation/desodiation, while the conductive network facilitates electron and ion transfer. The morphology evolution of MoS 2 /CNFs can be observed by tuning the amount of CNFs. The optimized MoS 2 /CNFs possesses expanded interlayer spacing of 0.71 nm, while the CNFs content is 10.24 wt%. As anodes for sodium ion batteries, it can deliver a capacity of 509 mA h g−1 at 0.1 A g−1, and maintains a high discharge capacity of 368 mA h g−1 after 400 cycles at 6.25 A g−1. Furthermore, reaction kinetics is analyzed, demonstrating the superior cycling stability and rate performance are rooted in the capacitive behavior. And the contribution ratio is calculated to be 72.7% at 1 mV s−1. [ABSTRACT FROM AUTHOR]