Preparation And Properties Of Two-dimensional Polypyrrole Sheets And Three-dimensional Ti₃C₂T_x/Polypyrrole Based Composite Hydrogels

In order to meet the needs of sustainable development of society,various renewable energy production technologies have been developed in the past few decades.At the same time,due to the intermittent and unstable nature of some renewable energy sources such as solar and wind energy,energy storage devices play an indispensable role in building sustainable energy output systems.Batteries and supercapacitors are the two most promising materials for widespread application in energy storage devices.Among them,batteries can provide great energy density,but they still suffer from slow energy transfer or absorption.Supercapacitors,on the other hand,are energy storage devices with high power density and longer cycle life than batteries.Therefore,the development of high-performance supercapacitors as energy storage devices has great application value and development prospects.Polypyrrole（PPy）,as one of the most important conducting polymers,has been extensively studied due to its high conductivity,environmental stability,redox properties as well as its promising applications in many fields.The main findings of the paper are as follows:（1）A novel structure of PPy rectangular“sheet”made of double-layers nanoparticles has been prepared in the presence of cationic surfactant cetyltrimethylammonium bromide（CTAB）,high concentration of propionic acid（PA）and pyrrole（Py）,wherein ammonium persulfate（APS）was used as oxidant.The influences of experimental conditions,i.e.,concentration of PA,CTAB and pyrrole in the reaction system,on the morphology of the PPy rectangular“sheet”have been systematically investigated.In addition,PPy nano-ring and nano-clip were also prepared with appropriate reaction conditions.Subsequently,the electrochemical properties of CTAB/PA/PPy sample was investigated.（2）Herein,a new strategy for the synthesis of Ti₃C₂T_x/PPy based hydrogels is reported based on PPy generated by in-situ polymerization of Py on the surface of Ti₃C₂T_xsheets.3D porous network structure of Ti₃C₂T_x/PPy,Ti₃C₂T_x/PPy/SWCNT and Ti₃C₂T_x/PPy/SWCNT/Lig hydrogels were prepared by hydrothermal treatment of Ti₃C₂T_xand Py;Ti₃C₂T_x,Py and single-walled carbon nanotubes（SWCNT）;Ti₃C₂T_x,Py,SWCNT and sodium lignosulfonate（Lig）dispersions,respectively.As-prepared samples show the compressive strength of 0.97 k Pa for the Ti₃C₂T_x/PPy hydrogel,1.53k Pa for the Ti₃C₂T_x/PPy/SWCNT hydrogel,and 0.60 k Pa for the Ti₃C₂T_x/PPy/SWCNT/Lig hydrogel,respectively.The high mechanical strength of the Ti₃C₂T_x/PPy/SWCNT hydrogel indicates that the added SWCNT can strong interact with PPy on the surface of Ti₃C₂T_xsheets.Meanwhile,as-prepared Ti₃C₂T_x/PPy,Ti₃C₂T_x/PPy/SWCNT and Ti₃C₂T_x/PPy/SWCNT/Lig hydrogels were separately assembled into symmetric supercapacitors（SSCs）with PVA-H₂SO₄gel electrolyte,which exhibit excellent specific capacitance(246.2,260.6 and 272.8 F g^-1)and good energy densities(6.92,7.33 and 7.67 W h kg^-1respectively at a power density of 450 W kg^-1).The proposed innovative strategy of in-situ formation of polymers on the surface of Ti₃C₂T_xacted as a likely cross-linking agent to prepare Ti₃C₂T_x/PPy based hydrogels is expected to construct 3D network structures of other functional materials.