Design,Synthesis And Electrocatalytic Performance Of 3D Porous Ti₃C₂T_x MXene Supported Metal Composite

Two-dimensional transition metal carbides,nitrides or carbonitrides(MXenes)have broad prospects in the field of electrocatalytic materials due to their large specific surface area,high metal conductivity,hydrophilicity,flexibility,and tunable structure.However,chemically exfoliated MXenes nanosheets are prone to self-restacking and lack of intrinsic catalytic active sites.Therefore,in-depth research on the rational design of MXenes is urgently needed to suppress the reduction of active area caused by selfstacking of MXenes,and increase the catalytic active sites to improve their intrinsic catalytic activity.In view of these problem,we make full use of the advantage of MXenes and metal materials to design and synthesize MXenes-supported metal composites.Design and synthesize functionalized MXene-supported Ir single atoms and MXene-supported CuFe alloy composites by gelationpyrolysis/pyrolysis method.and investigate their electrocatalytic hydrogen evolution and nitrate reduction performances,respectively.By controlling the amount of precursor,the material components can be quantitatively controlled to optimize the electrocatalytic performance of the material.Furthermore,combined with a variety of characterization and density functional theory(DFT)calculations to understand the source of the excellent catalytic performance.The main research contents are as follows:1.A novel catalyst consisting of Ir single atoms confined in porous heteroatom(N,S)co-doped Ti3C2Tx was successfully constructed through gelation-pyrolysis method,and used as hydrogen evolution reaction(HER)electrocatalyst.The optimal IrSA-2NS-Ti3C2Tx catalyst shows remarkable catalytic activity and stability towards HER in acidic and basic electrolytes.The IrSA-2NS-Ti3C2Tx shows a small overpotential of 57.7 mV and tafel slope of 25.1 mV/dec at a current density of 10 mA/cm2,maintains a long-term stability within 38 hours,and surpasses most of the recently reported MXenes based HER electrocatalysts.Meanwhile,S element plays a key role in the uniform dispersion of Ir single atoms is proved by X-Ray diffraction.In addition,X-ray photoelectron spectroscopy,X-ray Absorption Fine Structure(XAFS)combined with DFT calculations confirmed that the remarkable electrocatalytic performance of IrSA-2NS-Ti3C2Tx is due to the introduction of Ir single atoms and the N,S coordination;All results indicate that adjusting the N content can tune the oxidation state of the Ir single atom and the adsorption energy of the H*intermediate,achieving enhanced electrocatalytic HER performance within a certain range.2.A 3D porous Ti3C2Tx MXene-supported CuFe alloy nanoparticle composite(CuFe NP-Ti3C2Tx)was prepared by pyrolysis method and applied for electrocatalytic nitrate reduction reaction(NO3-RR)under neutral conditions.CuFe NP-Ti3C2Tx achieved high NRR activity,selectivity and stability in 0.1 M KNO3 solution,it achieved a 83.5%NH3 Faradic efficiency,a NH3 partial current density of 28.5 mA/cm2,and maintains a long-term stability within 16 hours;corresponding to a 20%increase in NH3 Faradic efficiency compared to 10Cu-ThC2Tx catalyst.The NO3-RR mechanism of CuFe NP-Ti3C2Tx was verified by material characterization and performance comparison test,in the NRR process,Cu acted as the active sites for nitrate adsorption and conversion.After forming CuFe alloy by adding Fe element,Fe adjusted the electronic structure of Cu,at the same time,H*adsorbed on Fe sites can promote nitrate deoxygenation and hydrogenation on Cu sites.The synergistic effect of the two elements resulted in excellent NO3-RR performance.In summary,IrSA-NS-Ti3C2Tx was successfully designed and synthesized for efficient hydrogen evolution electrocatalyst in this paper,and its sources of catalytic performance were explored,which provides an important reference for the systematic study of coordination interactions between single atoms and functionalized MXenes.Meanwhile,the Ti3C2Tx MXene supported CuFe alloy nanoparticle composite was successfully designed and synthesized for nitrate reduction reaction electrocatalyst,which confirmed the synergistic effect between Fe and Cu plays a key role in improvement of nitrate reduction activity and selectivity.It provides a new idea for rational design and in-depth study on the electrocatalytic mechanism of MXenes-supported metal composites.