Development And Performance Characterization Of MXenes-based Supercapacitors

Supercapacitor,as a good performance,efficient energy storage equipment,has attracted much attention in recent years,because of its ultra-high power density,excellent cycle stability,super long service life,fast charging and discharging advantages to make it shine in the field of sustainable energy.The low energy density is the key problem that restricts the further application of supercapacitors.We can expand the working voltage of supercapacitors by assembling asymmetric supercapacitors,in turn,the energy density of the supercapacitor is increased.The performance of supercapacitors is closely related to the selected electrode material.The anode material selected for this work is Ti₃C₂T_X@Ni O heterostructure and V₄C₃T_X@Ni O heterostructure,and the cathode material selects the RGO material treated with defects（DRGO）.2D transition-metal carbides/nitrides/carbonitrides（MXenes）have emerged as viable materials for ASC electrodes.For instance,MXenes has attracted great attention for ASC anodes particularly owing to its high metallic conductivity,excellent hydrophilicity,adjustable layer spacing,and rich redox-active sites.In fact,MXenes electrodes have displayed a high-rate performance,high power density,excellent cycling stability,and high energy density.Nevertheless,there are two major challenges with pristine MXenes.First,the terminal functional groups and surface defects formed in sample preparation may limit the specific charge storage capacity.Second,the strong van der Waals interactions between delaminated MXenes nanosheets can result in aggregation,which vastly reduces the specific surface area and limits ionic dynamic diffusion.To mitigate these issues,one effective strategy is to fabricate MXenes based heterostructures that combine the advantages of MXenes and pseudocapacitve materials.The abundant surface functional groups/defects and unique 2D hierarchical structure of MXenes render it possible to construct desired synergetic heterostructures with excellent structural stability,high specific capacitance,and excellent electrical conductivity.For instance,low-cost,stable Ni O features an ultrahigh theoretical specific capacitance of 3750 F g^-1 and is viewed as an attractive option to form heterostructures with MXenes.To prevent self-stacking,one viable option is to integrate the hierarchical MXenes@Ni O heterostructures into a 3D interlinked framework,which can also produce abundant active sites and facile ion/electron transfer pathways to significantly enhance the electrochemical kinetics.One method is to take advantage of the self-gelation of reduced graphene oxide（RGO）into a 3D mesoporous hydrogel that can be composited with various active materials to produce SC electrodes.The cathode material we prepared is RGO hydrogel with defect structure.The experimental results show that the r GO material with defect treatment has a significant improvement in the capacitance and porosity compared with the previous treatment.In this paper,a comprehensive study is conducted on the preparation and performance of MXenes-based supercapacitors.The main research results are as follows:.First,the Ti₃C₂T_X@Ni O heterostructure and V₄C₃T_X@Ni O heterostructure were synthesized by chemical liquid deposition and thermal annealing and characterized as follows:TEM,SAED,Raman,XRD,XPS,EDX.It presents an obvious two-dimensional layered structure,Ni O uniformly attached to the surface of MXenes material,HRTEM test showed a very clear lattice stripe,lattice spacing of 0.21nm,the rest of the spectral measurements further confirmed the successful synthesis of our heterostructures.Second,the Ti₃C₂T_X@Ni O-RGO hydrogel and V₄C₃T_X@Ni O-RGO hydrogel were prepared by low-temperature hydrothermal method.This scheme solved the self-stacking phenomenon between Ti₃C₂T_X and V₄C₃T_X layers.The results showed that the layer spacing was significantly larger after preparing the three-dimensional hydrogel.Take the Ti₃C₂T_X@Ni O-RGO hydrogel as an example:increased from 1.32 nm to 1.73 nm.At the same time,its pore structure was also significantly improved,and the mesoporous structure increased significantly,and the specific surface area increased from 86 m² g^-1 to 331 m²g^-1.Both large layer spacing and large specific surface area are crucial to improve the performance of supercapacitors.Third,conduct electrochemical testing of anode materials,including:CV,GCD,EIS,cycle,etc.The electrochemical tests show that our prepared materials have excellent electrochemical performance,the CV curve has obvious REDOX peak,showing obvious false capacitive characteristics,the specific capacitance value is up to 972.5 F g^-1;the cycle stability is good,retaining 95.4%of the initial capacitance value after 10000 cycles;the GCD curve shows obvious symmetrical triangle,which further confirms the reversibility of Faraday reaction.Fourth,DRGO hydrogels were synthesized by low-temperature hydrothermal method and catalytic gasification by Co.The defective RGO material has high electrical conductivity,rich pore structure and large specific surface area.We made a comprehensive characterization of DRGO,and its surface showed a fold structure with a uniform pore distribution,an average pore diameter of about 25 nm and a specific surface area of about 198 m² g^-1,which is a significant improvement over the original RGO.Fifth,after electrochemical testing like the anode material,the CV curve is quasi-rectangular,and the integral area is larger than the untreated RGO,which indicates that it has larger capacitance value and faster charge and discharge capacity;its multiplier performance and cycle stability are greatly improved than the RGO,thanks to the introduction of defect structure to improve its charge storage performance.Lastly,assembly of asymmetric supercapacitor:anode and cathode with the two kinds of electrode materials,through the assembly of asymmetric supercapacitor to improve its working voltage,and improve the energy density of supercapacitor,after measuring its energy density up to 86.22 Wh kg^-1,79.02Wh kg^-1 respectively,optimal and previously reported Ni and Mxenes based asymmetric supercapacitor.