Preparation And Design Of Ti₃C₂T_x MXene-Based Composites For High Performance Supercapacitors

MXenes,a new family of 2D layered transition metal carbides,nitrides or carbonnitrides,have been widely applied as pseudocapacitor electrodes in energy storage systems.Ti3C2Tx as one of the mostly studied MXenes possesses metallic conductivity,excellent hydrophilicity,outstanding stability and large interlayer spacing.Although Ti3C2Tx as supercapacitor electrodes possess high rate performance and excellent cycling stability,its capacity is relatively low.Using materials with high capacity to prepare composites with Ti3C2Tx is an effective route to solve the aforementioned problem.Moreover,Ti3C2Tx MXene will compensate for the unsatisfying rate performance and cycling stability of materials with high capacity(such as Fe3O4 and layered double hydroxides(LDHs)).Therefore,it is necessary to build Ti3C2Tx-based heterostructures.Herein,we constructed Ti3C2Tx MXene-based heterostructures and discuss its microstructures,phase formation,chemical compositions,supercapacitor performance and energy storage mechanisms in detail.The main contents are listed as followings:1.Laser crystallization strategy was applied to construct sandwich-like MXene/Fe3O4/MXene film electrodes on flexible Ni tapes.In 1 M Li2SO4 electrolyte,the areal capacitance(capacity)of MXene/Fe3O4/MXene reaches 46.4 mF cm-2(32.5 mC cm-2)at the current density of 0.5 mA cm-2,which is much larger compared to bare film electrodes(29.4 mF cm-2 or 20.6 mC cm-2).After 8000 charge-discharge cycles at the current density of 4 mA cm-2,the capacitance retention of MXene/Fe3O4/MXene is 96.3%.This work uses laser crystallization strategy to prepare MXene/TMOs films without causing severe oxidation of Ti3C2Tx.Thanks to the strong chemical interaction between MXene and Fe3O4 as well as the anchoring effect of MXene on Fe3O4,the electron transfer is greatly accelerated and the cycling stability is improved.2.To further improve the specific capacity of Ti3C2Tx-based composites,Ti3C2Tx/NiCoAl-LDH was prepared via hydrothermal method and then used for alkaline etching.Due to the increasing content of electroactive elements and the excellent conductivity of Ti3C2Tx,as-soaked composites exhbit battery-like behavior and possess a gravimetric capacity of 398 C g-1 at the current density of 1 A g-1.After 2000 charge-discharge cycles,76.6%gravietric capacity was maintained.3.In order to achieve the high loading mass and abundant exposure of active sites,we proposed the magneto-electrodeposition(MED)method to prepare Ti3C2Tx/NiCo-LDH composites with high loading mass.The microstructure of Ti3C2Tx/NiCo-LDH and the mass transport during electrodeposition process are tuned since of the magnetohydrodynamic(MHD)effect.An outstanding areal capacity of 3.12 C cm-2 was achieved at the current density of 1 mA cm-2,which is much higher than that of pristine NiCo-LDH(0.39 C cm-2).In summary,MED as a novel route to prepare Ti3C2Tx/NiCo-LDH greatly improves the electrochemical performance of Ti3C2Tx-based composites.4.MED strategy was used to incorporate different concentrations of Zn into NiCo-LDH in order to improve the cycling stability of Ti3C2Tx/NiCo-LDH.Since low magnetic fields are more favorable for manufacturing industry,the magnetic field of 1 T was used.The introduction of Zn greatly influences the microstructure,which improves the structural stability of samples.Moreover,Zn is able to protect electroactive mass from dissolution.With an optimal Zn concentration,Ti3C2Tx/NiCoZn-LDH exhibits an areal capacity of 1.34 C cm-2 at the current density of 1 mA cm-2.Moreover,composites preserve 94.0%of the areal capacity after 2000 charge-discharge cycles,which is superior to NiCo-LDH(63.6%).In summary,an appropriate incorporation of Zn via MED can achieve the preparation of Ti3C2Tx/NiCoZn-LDH with an excellent cycling stability.