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The combination of multiple electrode materials and their reasonable structural design are conducive to the preparation of composite electrodes with excellent performance. In this study, based on carbon nanofibers grown with Ni(OH)2 and NiO (CHO) prepared by electrospinning, hydrothermal growth, and low-temperature carbonization, five transition metal sulfides (MnS, CoS, FeS, CuS, and NiS) were hydrothermally grown on their surfaces, exhibiting that CHO/NiS had the optimal electrochemical properties. Subsequently, the effect of hydrothermal growth time on CHO/NiS revealed that the electrochemical performance of CHO/NiS-3h was optimal, with a specific capacitance of up to 1717 F g−1 (1 A g−1), due to its multistage core–shell structure. Moreover, the diffusion-controlled process of CHO/NiS-3h dominated its charge energy storage mechanism. Finally, the asymmetric supercapacitor assembled with CHO/NiS-3h as the positive electrode demonstrated an energy density of 27.76 Wh kg−1 at a maximum power density of 4000 W kg−1, and it still maintained a power density of 800 W kg−1 at a maximum energy density of 37.97 Wh kg−1, exhibiting the potential application of multistage core–shell composite materials in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti 3 C 2 T x MXene/carbon nanofiber electrodes are prepared by electrospinning. • The effects of Ti 3 C 2 T x MXene sheets size on the performances were investigated. • The electrodes (SMX/C) exhibit high-rate performance (90 F/g at 300 mV/s). • The electrodes have outstanding flexibility (98% retention after 500 bending). Increasing the capacitance and rate performance of the carbon-based electrodes used in flexible supercapacitors remains a key challenge for commercial viability. To meet these requirements, free-standing Ti 3 C 2 T x MXene/carbon nanofiber (CNF) electrodes were prepared by electrospinning of polyacrylonitrile (PAN) and carbonization for application as flexible supercapacitor electrodes. The effects of Ti 3 C 2 T x MXene size on fiber formation and electrochemical performance were investigated. Ti 3 C 2 T x MXene/CNF electrodes exhibited a specific capacitance of 90 F/g at a fast scan rate of 300 mV/s, which is almost 2.3 times higher than that of a pure PAN-derived CNF (38 F/g at 300 mV/s), while showing similar capacitance values of around 120 F/g at the slow scan rate of 2 mV/s. Due to the high degree of mechanical flexibility of CNFs, MXene/CNF based flexible supercapacitors also demonstrate long-term cycling stability (98% retention after 10 K charge-discharge cycles), and outstanding flexibility in dynamic bend tests. These results suggest that the MXene/CNFs have great potential for applications in flexible and versatile electronic devices. [ABSTRACT FROM AUTHOR]

Tailoring the chemical structures of a precursor polymer for carbon nanofibers (CNFs) produced by thermal treatment of electrospun nanofibers was studied to prepare the electrodes for electrochemical double layer capacitors (EDLCs). To improve energy storage performance of CNF electrodes, 6FDA-durene nanofibers were crosslinked by a vapor crosslinking method, and subsequently carbonized. Chemical modification via crosslinking was confirmed by FTIR spectra while the conversion of crosslinked 6FDA-durene into carbon was done by Raman spectroscopy. Electrochemical performance of these CNF electrodes was evaluated by assembling coin cells, and the CNFs derived from crosslinked 6FDA-durene nanofibers showed higher specific capacitances, energy densities and cycling stability than those from non-crosslinked ones. It was also shown that CNFs prepared using 1 min crosslinking exhibit the highest energy storage performances, a specific capacitance of 301 F g−1 (at 10 mV s−1), and the maximum energy density of 11.1 Wh kg−1 (at 0.5 A g−1) and power density of 1.8 kW kg−1 (at 6 A g−1). Surface area and porosity of CNFs, which is critical for the performance of EDLC electrodes, were studied by nitrogen adsorption/desorption measurements, and it was clearly seen that surface crosslinking of precursor polymers improved surface properties of the resultant CNFs. [ABSTRACT FROM AUTHOR]