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[Display omitted] • CoSe@NC nanofiber membrane was synthesized by electrospinning and thermal annealing method. • CoSe nanoparticles have strong adsorption and catalytic capability for polysulfides. • Li-S battery with CoSe@NC nanofiber membrane as interlayer shows excellent electrochemical performance. Lithium sulfur (Li-S) batteries have attracted tremendous attention due to their low cost and high theoretical capacity. However, the serious polysulfides shuttle and slow redox reaction kinetics hinder their large-scale commercial applications. Various attempts have been made to solve the problems. Herein, a CoSe@NC nanofiber membrane was prepared by electrospinning method and used as independent functional interlayer for the Li-S batteries. The visualized adsorption experiments show that the CoSe@NC nanofiber exhibits strong adsorption capability for polysulfides; In addition, CoSe nanoparticles with strong catalytic activity can accelerate the conversion of polysulfides. The adsorption-catalysis synergy of CoSe@NC can therefore effectively enhance the rate performance and cycling stability of Li-S batteries. The cell assembled with CoSe@NC functional interlayer delivers a high initial reversible discharge capacity of 1317 mAh g−1 at 0.1 C rate. After 200 cycles at 1.0 C, the capacity decay rate is only 0.16% per cycle. This work provides a feasible way to promote the electrochemical performance of Li-S batteries [ABSTRACT FROM AUTHOR]