Palladium Baced Catalysts Supported By Nonmetal-doped MXene For Ethanol Electrooxidation

With the continuous development of science and society,the increasing demand for energy,coupled with the concern about the destruction of the ecosystem and the increase in the consumption of non-renewable fossil energy,people have put forward a huge demand for clean and efficient energy.In recent years,direct ethanol fuel cells（DEFC）has the advantages of high energy conversion rate and environmentally friendly products,and has attracted the attention of scholars from various countries.However,in practical applications,it faces many challenges.The ethanol oxidation reaction（EOR）at the direct anode of ethanol fuel cells has the disadvantages of slow kinetics and incomplete oxidation.At present,metal Pd-based catalysts can effectively promote EOR and improve the utilization rate of ethanol fuel,but the by-products（such as CO）generated during the EOR process will occupy the active sites of Pd,reducing the activity and stability of the catalysts.At the same time,the Pd-based catalysts also have problems such as easy agglomeration of metal particles and few active sites.Therefore,how to obtain a new Pd-based catalyst with good catalytic activity,strong anti-poisoning ability and high stability is still a challenging task.It has scientific significance and application value for the preparation of high-performance fuel cell catalysts.Therefore,in this work,a heteroatom-doped two-dimensional MXene material（Ti₃C₂）was used as a support to synthesize a Pd-based composite catalyst with high electrocatalytic activity and stability.By changing the type and method of heteroatom doping,the microscopic morphology and electronic structure of Pd particles on the support were regulated.Through relevant characterization,electrochemical tests and theoretical calculations,the working mechanism of the catalyst was analyzed and explored,and the relationship between the catalyst composition,structure and catalytic performance for ethanol electrooxidation was clarified.The main research contents are as follows:（1）Application research on high-performance Pd-based nanocatalysts supported by N-doped Ti₃C₂In this work,a new type of Pd-based catalyst（Pd/N-Ti₃C₂-28 h）with obvious layered structure and uniform metal distribution was synthesized through hydrofluoric acid etching,NH₃·H₂O doping and metal Pd loading.The special layered structure of the Ti₃C₂support and the synergistic effect of NH₃·H₂O doping make the metal Pd and Ti₃C₂have higher binding energy and more abundant electron transfer.When Pd/N-Ti₃C₂-28 h catalyzed the electrooxidation of ethanol under alkaline conditions,it exhibited a current density of 36.71 m A·cm^-2,which was higher than that of Pd/Ti₃C₂-28 h and commercial Pd/C(12.73 m A·cm^-2).And Pd/N-Ti₃C₂-28 h has the advantages of high metal loading rate,large electrochemical active surface area and high electrochemical stability.After 200 redox cycles,the current density still has78.3%retention.Therefore,Pd/N-Ti₃C₂-28 h has a good application prospect as an anode catalyst for ethanol electrooxidation under alkaline conditions.（2）Changing the co-doping sequence of B and N,adjusting the electronic structure of Pd/MXene interface to enhance the catalytic performance of ethanol electrooxidationIn this work,the electrocatalytic performance of supported metals is enhanced by tuning the surface electronic structure.Based on two novel catalysts,Pd/B-N-Ti₃C₂and Pd/N-B-Ti₃C₂,the effects of the co-doping sequence of B and N elements on the electronic structure of the metal surface and the electrocatalytic performance of ethanol oxidation were explored.In the process of electrocatalytic ethanol oxidation reaction,the Pd/B-N-Ti₃C₂catalyst has the largest electrochemically active surface area,the highest peak current density and the strongest anti-toxicity compared with similar catalysts.Ddifferent doping sequences have different effects on the surface electronic structure and dispersion of supported metal Pd.Density functional theory（DFT）calculations show that the doping site of B on the support can absorb the H atoms that CH₃CH₂OH falls off,making the EOR proceed to a favorable path.This study provides new ideas for the synthesis of high-performance anode catalysts for ethanol fuel cells.（3）Dimethylamine borane-assisted one-step synthesis of B,N co-doped MXene-supported Pd catalystsIn this work,the co-doping of B and N atoms and the deposition of metal Pd on Ti₃C₂were achieved by a rapid one-step hydrothermal method,using dimethylamine borane as a heteroatom dopant and a metal reducing agent simultaneously.By exploring the electrocatalytic properties of ethanol oxidation,Pd/DMAB-Ti₃C₂exhibited higher electrochemically active surface area,ethanol oxidation current density,and electrochemical stability in electrocatalyzed ethanol than single-doped and undoped catalysts.The current density after 350 redox cycles can maintain 74.6%of the maximum current density.The B and N introduced when dimethylamine borane doped Ti₃C₂affected the electronic structure and d-band center of the supported metal Pd,thereby changing the adsorption strength of the catalyst to the EOR intermediates,improving the catalytic activity.This work provides a new idea for the rapid synthesis of high-performance element co-doped supported metal catalysts.