Rational design of hierarchically sulfide and MXene-reinforced porous carbon nanofibers as advanced electrode for high energy density flexible supercapacitors

In this study, in-situ carbon coating technology was used to embed the sulfide-loaded MXene in the carbon nanofibers through electrospinning to improve the sulfide conductivity and ion transfer rate. Polyacrylonitrile (PAN) with a high carbon conversion rate was used as carbon nanofiber, while polyvinylpyrrolidone (PVP) with a low carbon conversion rate was used as a pore-forming sacrificial agent. PAN–PVP-based porous carbon nanofibers (PCNF) with good meso/macropore structure were prepared via a thermally induced phase separation process. FeCo2S4 nanoparticles and ultra-thin Ti3C2Tx MXene were uniformly fixed in PCNF in situ, and a flexible hybrid film was prepared as the electrode material of supercapacitors (FeCo2S4/MXene/PCNF). The FeCo2S4/MXene/PCNF hybrid membrane inherits a three-dimensional pore structure and hierarchical PCNF nanostructure. It can provide continuous channels for the rapid electrolyte diffusion, thereby obtaining electrochemically active FeCo2S4 nanoparticles. Moreover, carbon nanofibers can act as a conductive core for providing effective electron transport for the rapid Faraday redox reaction of the FeCo2S4 sheath or as a buffer matrix for reducing local volume expansion/contraction during long-term cycling. Therefore, the optimized FeCo2S4/MXene/PCNF hybrid membrane has excellent cyclic stability, which fundamentally solves the problems of poor sulfide conductivity and cyclic stability.