Interfacical Engineering Of MXenes Composites And Applications In Energy Storage Batteries And Water Splitting

MXenes refer to a novel two-dimensional transition metal carbides and nitrides.In this paper,three kinds of MXenes,such as Ti₃C₂,Ti₂N,Ti₃CN and Nb₂C,were prepared.A variety of electrode materials were prepared by interfacial engineering methods like element doping,self-assembly and heterojunction structure,which were applied to the anode of lithium-ion batteries,the electrodes of overall water splitting,the cathode of lithium-sulfur batteries and the cathode of zinc-air batteries.In this paper,Common isues such as electrode material preparation,electrode interface design and electrode catalytic performance are studied in this paper.It is an important symbol to help achieve carbon neutrality by green energy development.MXene-based nanocomposites can explore some light for the material design of green energy.The specific contents of the disseration are as follows:（1）In this work,we present an interfacial superassembly by engineering the Mo Se₂nanoflowers coupled with ribbon-like Ti₂N MXene frameworks（Mo Se₂@Ti₂N MXene）.The Mo Se₂@Ti₂N MXene hybrids have excellent electrochemical performance and are used as the anodes for lithium-ion batteries（LIBs）.Electrochemical analysis indicates that the ribbon-like Ti₂N MXene frameworks not only help to avoid side reactions on carbides in LIBs,but also contribute to outstanding rate capacity and superior specific capacity,thus achieving ultra-stable long-life cycle performance.The Mo Se₂@Ti₂N MXene electrode reveals a reversible specific capacity of 806 m Ah·g^-1 at 0.1 A·g^-1 after 200 cycles.It maintains the capacity of 486.2 m Ah·g^-1 after 2000 cycles at 1.0 A·g^-1,indicating satisfactory cycle stability.The new-type interfacial superassembly can provide a novel synthesis strategy for anode electrodes to improve the LIBs performance.（2）Metal-organic frameworks-derived Co P anchored on MXene toward an efficient bifunctional electrode with enhanced lithium storage.Herein,we have prepared the metal-organic frameworks-derived Co P anchored on Ti₃C₂ MXene（MOFs-Co P@MXene）and fully explored its synergy as an efficient bifunctional electrode for enhanced lithium storage for the first time.It is gratifying that the prepared MOFs-Co P@MXene provides a high capacity of 706.5 m Ah·g^-1 after 200 cycles at 0.2A·g^-1,as the anode for LIBs.It can provide 585.8 m Ah·g^-1 after 1000 cycles with 0.5A·g^-1.The MOFs-Co P@MXene anode has robust lithium-ion storage capacity,indicating that it can increase the charge transfer rate and improve Li⁺diffusion kinetics with enhanced electrochemical activity.As lithium-sulfur batteries（LSBs）cathode,MOFs-Co P@MXene/S shows 796.9 m Ah·g^-1 after 300 cycles at 0.2 C.MOFs-derived Co P coupling with MXene exhibits enhanced capture capacity of sulfur,facilitating the conversion of polysulfides.The results show that the MOFs-Co P@MXene composite are feasible as both the anode of LIBs and the cathode of LSBs.（3）Ti₂NT_x MXene composites were used for overall water splitting based on the experience of the interfacial design of Ti₂NT_x MXene.This research compared with two systems between Ni-Mo Se₂/Ti₂NT_x and Ti₂NT_x@MOF-Co P.In the first work,we prepaered heterostructure nanohybrids of Ni-doped Mo Se₂ coupled with Ti₂NT_x toward enhancing overall water splitting.In short,Ni-Mo Se₂/Ti₂NT_x exhibits a low overpotential（η=92 m V）at a current density of 10 m A·cm^-2 and Tafel slope(79.7m V·dec^-1)for HER performance in 1 M KOH.In terms of OER performance,Ni-Mo Se₂/Ti₂NT_x displays remarkable overpotential(270 m V at 50 m A·cm^-2)and Tafel slope(81.1 m V·dec^-1).In the overall water splitting configuration,Ni-Mo Se₂/Ti₂NT_xelectrodes used as bifunctional electrocatalysts only need 1.59 V at 10 m A·cm^-2.In the second work,we prepaered ultrathin Ti₂NT_x MXene-wrapped MOF-derived Co P frameworks towards hydrogen evolution and water oxidation.The Ti₂NT_x@MOF-Co P electrode shows competitive hydrogen evolution performance in a wide p H-range(current density of 10 m A·cm^-2)and has a low overpotential of 112 m V in p H=14especially.The Ti₂NT_x@MOF-Co P electrode for OER also has a lowη=241 m V at 50m A·cm^-2.Based on the bifunctional activity of Ti₂NT_x@MOF-Co P in alkaline,we set a dual-electrode configuration for HER and OER.It has a bias of 1.61 V at 10 m A·cm^-2,with impressive catalytic stability during a 20-hour measurement.The results show that the two catalysts have advantages and disadvantages;The former has better HER performance and the latter has better OER performance;There is still to be enhanced for improvement in the bifunctional water splitting.（4）Ni-Doped Ti₃CNT_x coated nanoporous covalent organic frameworks（COFs）were prepared to accelerate hydrogen diffusion for efficient HER,based on the research of Ti₃C₂ andd Ti₂N MXene.The reason for the slow HER is mainly that the accumulation of generated hydrogen near the active site hinders the efficient progress of HER.In this work,Ni-doped Ti₃CNT_x coated with nanoporous COFs（Ni-Ti₃CNT_x/COF,abbreviated as NMXC）was prepared to improve the diffusion concentration gradient of hydrogen,so that the HER can be carried out efficiently.The doped nickel can improve the catalytic activity of the conductive Ti₃CNT_x MXene.The results show that the Tafel slope of Ni-Ti₃CNT_x/COF(the concentration of Ni in Ti₃CNT_x is 0.3%,abbreviated as N_0.3MXC)is as low as 46.2 m V·dec^-1 at a current density of 10 m A·cm^-2 in 0.5 M H₂SO₄.In the long-term stability test of solar power supply,the current density decreased by only 7.8%after 18 hours.The first-principles calculations show that the introduction of Ni significantly improves the catalytic activity(|ΔG_H*|can be as low as 0.06 e V).At the same time,the calculation of hydrogen adsorption energy and molecular dynamics simulation show that there is a significant difference in hydrogen concentration gradient on the surface of NMXC composite,which is beneficial to the diffusion of generated hydrogen molecules.This kind of structural engineering can provide some enlightening significance for the study of gas catalyst interface in HER.（5）Oxygen-terminated Nb₂CO₂ MXene with interfacial self-assembled COF can be used as bifunctional catalysts for durable zinc-air batteries（ZABs）.The desirable air cathode in ZABs,which can effectively balance oxygen evolution and oxygen reduction reactions not only needs to adjust the electronic structure of the catalyst,but also needs a unique physical structure to cope with the complex gas-liquid environment.In this work,COF-LZU1 was self-assembled on the interface of Nb₂CO₂ MXene（Nb₂CO₂@COF）for the first time.The Nb₂CO₂@COF electrode has excellent OER/ORR overpotentials with the potential difference（ΔE）of 0.79 V.When applied to the configuration of ZABs,Nb₂CO₂@COF shows a power density of 75 m W·cm^-2 and favorable long-term charge/discharge stability,so it can be used as a potential candidate cathode for noble metal-based catalysts.first-principles calculations are carried out to prove that oxygen-terminated Nb₂CO₂ MXene plays an active role in enhancing the sluggish reaction of oxygen intermediates.Nb₂CO₂ MXene can also stimulate the spatial accumulation of discharge products,which is beneficial to improve the stability of secondary ZABs.Molecular dynamics simulation is used to show that the confinement effect of COF can effectively regulate the concentration of O₂ on the surface of Nb₂CO₂@COF,which is conducive to the efficient and durable reaction.This idea of combining MXenes and COFs sheds some light on the design of ZABs.