Characterization Of MXene And Heterostructures Electrochemical Energy Storage Materials

In recent years,the problems of energy shortage and environmental pollution have become increasingly prominent.Electrochemical energy storage can effectively alleviate global energy and environmental problems.Secondary ion battery energy storage devices have high energy density,small size and easy to carry,high operating voltage,high safety performance and clean and pollution-free,etc.,which are widely studied and applied by people.Lithium ion battery is the most common secondary ion battery.However,lithium resources are scarce and expensive,which is not conducive to large-scale energy storage equipment.Therefore,the most effective solution is to develop a new type of secondary ion battery instead of lithium ion battery.Because Na and Li are in the same main group,have similar electrochemical properties,and because Na is widely distributed in the earth’s crust at low cost,sodium ion batteries(NIBs)have become an important object of research.Electrode material is one of the important factors affecting the electrochemical performance of batteries,so it is particularly important to study appropriate electrode materials to improve the electrochemical performance of batteries.In recent years,two-dimensional materials have been considered ideal as anode materials for secondary ion batteries due to their unique structure.Two-dimensional transition metal carbon-nitride(MXene)with a large specific surface area,which not only provides a large spatial specific surface area for ion storage,but also provides a channel for ion diffusion,thus enabling high capacity and fast charge/discharge functions.Therefore,MXene materials have been studied by many researchers as anode materials for secondary ion batteries.However,two-dimensional MXene materials also have their shortcomings,for example,the conductivity of single-layer MXene structures is not very good and the stacking effect between layers tends to occur.To overcome this disadvantage,we composite MXene and graphene layers to form Graphene/MXene heterostructure.Although our theoretical analysis shows that the G/MXene heterostructure outperforms the monolayer MXene structure,the exact results need to be confirmed by theoretical calculations.Therefore,Ti2CO2 as the representative of MXene,through the first principle calculation method,we systematically studied the electron,adsorption,diffusion,open circuit voltage,Na storage capacity,mechanical properties of Ti2CO2 and G/Ti2CO2 heterostructure.The calculation results show that,for Ti2CO2,the band structure have the characteristics of semiconductor.The Hc site is the most stable adsorption site for Na,the adsorption energy is-1.4eV,the diffusion barrier is 0.21eV,the maximum sodium storage capacity is 478mAh/g,the average open circuit voltage is 0.68V,and the in-plane Young’s modulus is 161.40GPa.As for the G/Ti2CO2 heterostructure,its energy band structure has the characteristics of a conductor,Na is most stably adsorbed at the HC-I position with an adsorption energy of-1.26eV,the diffusion potential barrier is 0.14eV,the maximum Na storage capacity is 528mAh/g,the average open circuit voltage is 0.51V and the in-plane Young’s modulus is 364.82GPa.Compared to the monolayer Ti2CO2 structure,the G/Ti2CO2 heterostructure has a lower diffusion potential barrier and a faster diffusion rate,a smaller open circuit voltage and provides a larger output voltage,a greater Na storage capacity.However,the adsorption energy is slightly smaller than that of Ti2CO2 due to the fact that there is a partial charge transfer from the graphene layer to the Ti2CO2 layer in the G/Ti2CO2 heterostructure,resulting in a weaker adsorption capacity.Therefore,G/Ti2CO2 heterostructure is a potential electrode material for sodium ion batteries.In addition to Na ion energy storage,we also studied the energy storage characteristics of hydrogen production from water electrolysis catalyzed by Fe and Co doped graphene.Hydrogen production from electrolytic water is a clean energy storage methon,which uses H2O as raw material and is realized through oxidation and reduction reaction.Hydrogen energy is considered as one of the ideal candidate energy sources on account of its rich resources,high energy and environmental friendliness.Hydrogen production by electrolysis of water is a clean energy solution.Its principle is to store the hydrogen from electrolytic water,and convert the stored hydrogen into electric energy through fuel cells or other ways when electric energy is needed.In this paper,two common metal elements,Fe and Co,are selected as catalysts,study the oxygen evolution reaction of Fe and Co on three kinds of substrate anodes(OER)that may be formed by graphene/MOF heterostructure materials after high temperature heat treatment and the research shows that Fe has good catalytic performance on defective graphene.