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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]

An efficient, robust and low-cost bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential to high-performance zinc-air batteries (ZABs). Metal-nitrogen-carbon (M-N-C) systems have attracted considerable attention recently. Herein, a novel Co-N x -enriched electrospun porous carbon nanofibrous bifunctional electrocatalyst (Co-N x /EPCF) is prepared by electrospinning with cobalt nitrate and SiO 2 , followed by carbonization and acid etching. The catalyst displays an outstanding electrocatalytic activity of reversible oxygen overpotential (ΔE = E j = 10 - E 1/2 = 0.87 V), as well as a high stability. The first-principal calculation reveals that the Co–N–C structure has better ORR paths than that of Co cluster. Furthermore, based on the electrocatalyst, the assembled flexible ZABs possess a power density of 81 mW cm−2, a capacity of 807 mAh g zn −1, and 111 stability cycles. The study provides a novel strategy to prepare high-performance bifunctional catalysts for wearable power sources. [Display omitted] • Electrospun porous carbon nanofibers are prepared by hard template method. • Co-N x -enriched catalyst drives energy-efficient ORR/OER kinetics with ΔE = 0.87 V. • Flexible ZABs achieve a power density of 81 mW cm−2 and a cycle time of 37 h. [ABSTRACT FROM AUTHOR]

The in-situ immobilization of Co/MnO hetero-nanoparticles onto N,S co-doped carbon nanotubes/nanofiber-integrated hierarchical branched superstructures demonstrates excellent oxygen reduction electrocatalytic activity, stability and performs robust cycling stability. [Display omitted] • The Co/MnO hetero-nanoparticles were immobilized onto carbon nanofibers. • The heterojunctions cause electronic redistribution and create more active sites. • The "branches"/"trunk"-structure could accelerate electrolyte and mass transport. • The Co/MnO@N,S-C NT/NFs-equipped Zn-air battery shows superior cycling stability. Electronic regulation via interfacial formation is identified as a versatile strategy to improve the electrocatalytic activity. Herein, we report a feasible electrospinning-pyrolysis approach for the in-situ immobilization of Co/MnO hetero-nanoparticles onto N,S co-doped carbon nanotubes/nanofiber-integrated hierarchical branched superstructures (abbreviated as Co/MnO@N,S-C NT/CNFs hereafter). The simultaneous realization of interfacial engineering and nanocarbon hybridization renders the fabricated Co/MnO@N,S-C NT/CNFs with abundant firmly anchored active sites, modified electronic configuration, improved electric conductivity, efficient mass transport pathways, and significantly reinforced stability. Profiting from the compositional synergy and architectural advantages, the Co/MnO@N,S-C NT/CNFs exhibit outstanding ORR activity, superior tolerance to methanol, and excellent long-term stability in KOH electrolyte. More encouragingly, as a proof-of-concept demonstration, the rechargeable aqueous and flexible all-solid-state Zn-air batteries using Co/MnO@N,S-C NT/NFs + RuO 2 as the air-cathode afford higher power densities, larger specific capacities and superb cycling stability, outperforming the state-of-the-art Pt/C + RuO 2 counterparts. This work demonstrates the great contribution of heterointerfaces for oxygen electrocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed a new type of Fe 3 C-N-C nanofibers as oxygen reduction catalyst. • Dicyandiamide can increase specific surface area and generate active sites for ORR. • Synergistic effect between N-doped carbon and Fe 3 C can enhance the ORR performance. • Zn-air battery with Fe 3 C-N-C-0.5 delivers high power density and cycling stability. Slow oxygen reduction reaction (ORR) kinetic at the cathode side of Zn-air batteries seriously hinder its large-scale applications. Here, dicyandiamide (DCD) was used to synthesis high specific surface area ORR electrocatalysts by electrospun. The as-synthesized Fe 3 C nanoparticles decorated N-doped carbon nanofibers exhibit comparable performance to commercial Pt/C catalysts. Rechargeable Zn–air batteries with the catalyst exhibits higher power density and cycling stability compared to the commercial Pt/C catalyst. This work has demonstrated a new way to prepare highly efficient and stable ORR electrocatalysts for rechargeable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Developing transition-metal based bifunctional electrocatalysts to efficiently drive oxygen evolution reaction and oxygen reduction reaction is an urgent demand for the implementation of rechargeable Zn-air batteries. Transition-metal sulfides are emerging as alternatives to precious metal-based electrocatalysts, however, their bifunctional activities are usually restricted by inferior electrical conductivities and limited electrochemical active sites. Herein, we highlight a novel metal-organic frameworks derived nitrogen-doped carbon nanofiber coupled FeS 2 –CoS 2 (FeS 2 –CoS 2 /NCFs) by a combination of electrospinning and atomic-layer-deposition approach. Benefiting from the large exposed surface active sites of hierarchical structure and the abundant interfacial vacancies in FeS 2 –CoS 2 heterointerface, the FeS 2 –CoS 2 /NCFs integrated electrocatalyst delivers a high bifunctional activity together with a good durability in alkaline medium. Notably, the liquid Zn-air battery assembled with this FeS 2 –CoS 2 /NCFs electrode displays a considerable peak power density of 257 mW cm−2, a high specific capacity of 814 mA h g−1 and a long cycling life of 250 h, superior to precious metal based Zn-air batteries. Moreover, the flexible solid-state Zn-air battery using such FeS 2 –CoS 2 /NCFs electrode can stably power LED panels even under twisting state, demonstrating practical potentials in wearable and portable electrochemical devices. Image 1 • Hierarchical FeS 2 –CoS 2 /NCFs with core-shell structure was designed. • FeS 2 –CoS 2 /NCFs displayed efficient bifunctional catalytic activities. • The interfacial vacancies and hierarchical structure increased its activities. • FeS 2 –CoS 2 /NCFs-based batteries exhibited excellent power density and cycling durability. [ABSTRACT FROM AUTHOR]