| With its good mechanical properties,excellent electrical conductivity,hydrophilicity and tunable surface chemical activity,MXene has great application potential in the field of energy storage.However,due to the effect of interlayer van der Waals forces,MXene nanosheets tend to restack and aggregate during assembly,which greatly reduces the specific surface area and limits the accessibility of electrolyte ions or electrons,thus affecting their electrochemical performance.Design and construction of three-dimensional（3D）porous MXene macro-structure with abundant pore structure is conducive to exposing its active surface and significantly improving its electrochemical performance,which is a hot topic in the field of electrode construction and energy storage mechanism research.Recently,researchers have proposed a variety of construction strategies for 3D porous MXene structures,but there are still shortcomings in the control of pore size and number,electron transport mechanism with tunable pore structure,and improvement of electrochemical performance.To solve these problems,it is of great significance to construct 3D porous MXene structures with matching pore size and adjustable porosity,and to explore the relationship between structure（pore structure,composition,surface properties）and the electrochemical performance.In this paper,focusing on the exploring and optimizing the pore structure and properties,three kinds of macro-3D MXene films supported by different templates with adjustable microstructure were designed and constructed.Meanwhile,the transfer mechanism of electrons and electrolyte ions in porous electrodes was deeply understanded,then the relationship between structure（pore structure,composition,surface properties）and the electrochemical performance was studied systematically.The main contents are as follows:（1）Flexible 3D porous MXene films were successfully constructed by using natural rubber latex（NRL）with a uniformly distributed sub-macroparticle as a sacrifice template instead of high-cost artificial template.The abundant pores between layers effectively alleviate the stacking of MXene nanosheets and accelerate the transfer of electrons and electrolyte ions between layers.By varying the loading amount of NRL,a controllable change in the porous size in the range of 100-500 nm was achieved.When the NRL load reaches 70%,the porous MXene electrode（MXF-70%）exhibits an optimal specific capacitance of 480 F g-1(scan rate of 2 mV s-1),good rate performance(202 F g-1specific capacitance at 1 V s-1),lowest ion diffusion resistance,and excellent cycle stability(capacitance retention of 97.1%after 10,000 cycles at a scan rate of 50 mV s-1).（2）Three kinds of 3D porous MXene films with significantly different pore size structures were prepared using polystyrene（PS）microspheres with different diameters（80,310 and 570 nm,respectively）.MXene nanosheets are coated on the surface of PS microspheres by electrostatic action,and the prepared porous film provides a high gravimetric capacitance of 474 F g-1at a scanning rate of 2 mV s-1.By adjusting the mass ratio between MXene and PS microspheres,the degree of interlayer pore accumulation can be accurately regulated,thereby affecting the internal resistance of the porous electrode.After further introduction of carbon nanotubes（CNTs）to improve the conductivity,the prepared composite porous film provided a high specific capacitance(2 mV s-1)of 462 F g-1,and effectively improved the contact resistance of the electrode,achieving a good capacitance retention rate of 44.3%(1 V s-1).In addition,the assembled flexible symmetrical supercapacitor provides a maximum energy density of 10.82 Wh kg-1at a power density of 102.9 W kg-1,and still has a capacitance retention rate of 98.6%after 5000 cycles,showing excellent cycle stability.（3）Three mesoporous hollow carbon spheres with different surface pore sizes（6.40,7.83and 12.7 nm,respectively）were prepared,and a method to construct a 3D porous MXene structure without removing the template process was proposed using mesoporous hollow carbon spheres（MHCS）as a template.While alleviating MXene nanosheet stacking,the pores on the surface of MHCS can also accelerate electrolyte penetration.The prepared composite film exhibits a high specific capacitance of 397 F g-1(2 mV s-1),excellent cycle life（capacity can still maintain 91.5%after 10,000 cycles）,and excellent rate performance(capacitance retention rate of 60.7%at 1 V s-1),which was further increased to 68.3%when CNT was introduced.The symmetrical supercapacitor assembled with this composite film provides a maximum energy density of 14.48 Wh kg-1at a power density of 267.32 W kg-1and exhibits good cycling stability（after 10,000 cycles,it still provides 86.7%of the initial capacitance）. |
PDF Full Text Request