Ti3C2Tx MXene as a growth template for amorphous RuOx in carbon nanofiber-based flexible electrodes for enhanced pseudocapacitive energy storage

A noble surface engineering method was developed to create a binder-free flexible electrode comprising Ti3C2Tx MXene/carbon nanofibers (MCNFs) covered by amorphous RuOx with a combined electrospinning and hydrothermal process. Utilizing the hydrophilicity of the MXene on/in the MCNFs, RuOx was easily coated on the surfaces of the MCNFs through oxygen-mediated chemical bonding between the functional groups of the MXene and Ru ions. A structural analysis revealed that the MXene acted as a growth template for RuOx and that the formed RuOx had an amorphous and disordered state in the composite electrode, which impacted the electrochemical performance. The electrochemical tests showed that these composite electrodes improved the electrochemical performance, with a two-fold increase in the gravimetric capacitance (279.4 F/g at 2 mV/s) relative to that of pristine MCNFs, a wide potential window (from 0.7 to 1 V) providing a superior energy density of 8.5 Wh/kg at a power density of 85.8 W/kg, as well as long-term cycling stability (99% after 10,000 cycles). The synergetic effect of the RuOx and MXene in the composite electrodes was attributed to an enhanced pseudocapacitive reaction. Our novel electrodes and fabrication method confirm the great potential of CNF-based composites for the development of high-performance binder-free electrodes for supercapacitors.