Fe7Se8 nanoparticles encapsulated by CNT reinforced fibrous network with advanced sodium ion storage and hydrogen evolution reaction

•A rational strategy for constructing CNT reinforced fibrous network was developed.•The mechanism of electrochemical performance of the electrodes has been investigated.•Fe7Se8/CNT/C electrode exhibited excellent Na+ storage properties and HER activity. Sodium ion batteries (SIBs) has been regarded as one of the most promising large scale energy storage devices. Besides, hydrogen production by water splitting is the green, safe and low cost long-term energy conversion and storage technology. Rare studies have reported advanced electrode materials for both SIBs and HER. Herein, Fe7Se8 nanoparticles have been successfully encapsulated into CNT reinforced fibrous network (Fe7Se8/CNT/C) by electrospinning combined with in situ selenide process. When utilized as flexible anodes for SIB, the Fe7Se8/CNT/C delivers superior rate capabilities (524 mAh g−1 even at 5000 mA g−1) and cycling stability (610 mAh g−1 at 500 mA g−1 after 1000 cycles). Moreover, the Fe7Se8/CNT/C also delivers considerable hydrogen evolution reaction (HER) activity (an overpotential of 138 mV at a current density of 10 mA cm−2 and a Tafel slope of 114 mv dec−1). Ex-situ electrochemical mechanism studies including EIS, GITT, CV and ECSA reveal that the graphitized CNT reinforced fibers can accelerate the ions/electrons transportations and the robust fibrous network structure guarantees excellent structural stability, thereby, preventing the aggregations of Fe7Se8 nanoparticles, facilitating electrolyte penetration and creating numerous catalytic active sites. Therefore, the Fe7Se8/CNT/C is one of the most promising energy storage and conversion materials. The fabrication strategy in this work could give an insight in exploring advanced functional materials. [Display omitted]