Preparation And Electrochemical Properties Of Colloidal Titanium Carbide Nanosheets With Nitrogen Doping

The unique physical and chemical properties of two-dimensional materials due to their nanometer thickness have attracted great interest of researchers.As a new two-dimensional material,transition metal carbide/nitride/carbonitride(MXene)are widely used in energy storage,catalysis and other fields due to their high conductivity and electrochemical activity.Heteroatom doping can adjust the electronic structure characteristics of materials and is one of the effective strategies to improve the properties of materials.Heteroatom doping is one of the effective strategies to improve the properties of materials,which can adjust the electronic structure characteristics of materials.Although nitrogen incorporation into MXene lattices has been reported,these methods are prone to cause problems such as difficult to delaminate bulk MXene,flocculation and oxidation of MXene nanosheets,which to some extent limits the improvement of MXene performance.Dispersed two-dimensional nanosheets colloid is of great significance for the application of two-dimensional materials in liquid phase technology,so it is urgent to develop a new strategy for effectively doping MXene lattices while forming colloidal solutions.In our work,the preparation of colloidal solution of nitrogen doped MXene nanosheets was realized by fine adjusting the annealing temperature and controlling the surface chemical characteristics of the materials,which avoided the problems of difficult delamination of bulk MXene,irreversible restacking of monolayer MXene and oxidation by traditional methods,and the obtained colloid had good dispersion and stability.Through a series of characterization and electrochemical tests,its structure and properties were studied in detail as follows:(1)Preparation of colloidal Ti3C2 nanosheets with nitrogen dopingA multilayer Ti3C2 was prepared by etching Al layer in Ti3AlC2 using HCl+NH4F as etching fluid.At the same time,NH4+ was spontaneously embedded between Ti3C2 layers;Then annealed in inert gas,NH4+binds to surface OH-and converts to NH3,incorporating nitrogen atoms into Ti3C2 lattice in situ.By fine adjustment of annealing temperature to control its effect on the surface chemical characteristics of the material,nitrogen incorporation into Ti3C2 lattice was achieved while maintaining the hydrophilic characteristics of the material surface,which is beneficial for further ion intercalation and exfoliation to obtain the hydrocolloid solution of nitrogen doped Ti3C2 nanosheets.In this paper,an effective strategy for the preparation of nitrogen doped MXene colloids is proposed,which facilitates the application of nitrogen doped MXene in liquid phase engineering and is of great significance for the development of a variety of device structures with high controllability and repeatability.(2)Characterization of colloidal Ti3C2 nanosheets with nitrogen dopingBenefiting from the retention of hydrophilic groups on the surface of the material,the obtained colloidal has excellent dispersion and stability,which is more conducive to the preservation of colloid.Ultraviolet absorption spectra show that the ultraviolet absorption of nitrogen doped Ti3C2 colloid shows a clear red shift relative to Ti3C2 colloidal,thus the nitrogen doped Ti3C2 colloid presents a gray black color different from that of Ti3C2 colloid.The thickness of nitrogen doped Ti3C2 nanosheets in colloid was determined as single or double layers using atomic force microscopy.Through density-of-state calculation and X-ray photoelectron spectroscopy characterization,the electron density of nitrogen doped Ti3C2 increased significantly and new nitrogen-containing structures such as pyrrolic nitrogen with electrochemical activity are formed,which endowed nitrogen doped Ti3C2 with higher conductivity and more reactive active sites,thus creating conditions for its electrochemical applications.(3)Electrochemical performance test and application of Ti3C2 nanosheets with nitrogen dopingThe electrochemical properties of nitrogen doped Ti3C2 were tested in acidic electrolyte.Based on the synergistic effect of nitrogen doping to improve the in plane conductivity of materials and new redox active sites,the electrodes prepared by nitrogen doped Ti3C2 dropwise coating on carbon cloth have high specific capacity(586 F g-1)and excellent rate performance,which maintain excellent electrochemical performance even after being prepared into thin film electrodes by vacuum suction filtration.In order to solve the problems of small operating voltage range and low energy density of symmetric capacitors,flexible asymmetric supercapacitors were constructed with polypyrrole/reduced graphene oxide,which have a working voltage interval of 1.4 V,and the highest energy density reached 32 W h kg-1 while maintaining power density of 821 W kg-1.The device can effectively provide energy for electronic equipment,and maintain its excellent performance even under bending conditions.Our approach presented a feasible strategy for achieving colloidal nitrogen doped MXene,which are promising building blocks for applications in versatile MXene-active fields.