Synthesis,Transformation,and Performance Of Noble-Metal Tellurium-Based Nanomaterials

In the past decades,noble-metal chalcogenides,as an emerging class of nanomaterials possessing advantages of both noble-metal nanomaterials and traditional transition-metal chalcogenides,have achieved considerable progress in terms of material preparation and performance development,especially in the nanoscale electronic,optoelectronic,and sensor applications.However,the report of noble-metal chalcogenides in electrocatalytic applications is relatively rare.In addition,compared with more extensive research reports for noble-metal sulfide and noble-metal selenide,there is still a lot of room for improvement in the preparation methods and performance development of noble-metal tellurium-based nanomaterials.This is mainly due to the stronger semi-metal property of tellurium,leading to the relatively unique physical and chemical properties of noble-metal tellurium-based nanomaterials.Although the particularity makes this kind of nanomaterials difficult to be developed and prepared,they have great potential applications in many fields.This thesis focuses on the controlled preparation and performance development of noble-metal tellurium-based nanomaterials.Based on the liquid phase chemical reduction method,a series of platinum-tellurium（Pt-Te）and palladium-tellurium（Pd-Te）nanomaterials have been developed,and the corresponding electrocatalytic applications have been developed according to their structural characteristics.Based on the cation exchange method,we have creatively developed a simple and versatile preparation strategy for the direct synthesis of noble-metal tellurium-based nanomaterials.The research works are as follows:（1）An effective liquid phase chemical reduction method was developed to achieve the preparation of ultrathin PtTe₂ nanosheets with regular morphology through the synergistic regulation of carbon monoxide and formic acid.Subsequently,the Te component was etched by electrochemical method,and the porous ultrathin Pt nanosheets with highly distorted structure were successfully obtained.The porous ultrathin Pt nanosheet with distorted structure on the surface has a great promotion effect on the improvement of electrocatalytic oxygen reduction performance.Further theoretical calculations show that the nanosheets with surface distortion possess abundant Pt active sites with low coordination.These Pt active sites can act as electron consumption centers and effectively transfer electrons to oxygen species,thus greatly improving their electrocatalytic oxygen reduction performance.（2）An effective liquid-phase chemical reduction method was developed to prepare a new type of PtTex superstructure comprised of ultrathin nanosheets through the coordinated regulation of carbon monoxide and benzoin.The composition and crystal phase of the structure were highly controllable.Through further electrochemical etching,Pt superstructures with different distortion levels were systematically prepared.Due to the robustness of the superstructure,this nanomaterial not only shows high activity,but also shows excellent stability in electrocatalytic oxygen reduction reaction,methanol electrooxidation reaction and hydrogen evolution reaction.Further theoretical calculations show that there are surface compressive strains,surface defects and nano voids widely distributed on the porous Pt nanosheets after electrochemical etching.Under the synergistic effect of these distorted structures,the Pt superstructures can significantly improve the related electrocatalytic performance.（3）Te doped Pd nanocrystals（Te-Pd NCs）were prepared by a simple one-pot method.The surface of Pd nanocrystals was modified by doping a small amount of Te.The material exhibits high Faraday efficiencies of carbon monoxide（CO）and ammonia（NH3）in CO₂ electroreduction（CO₂RR）and nitrite electroreduction（NO₂RR）,respectively.Based on its catalytic properties,we further investigated the electrochemical performance for urea production in the CO₂RR and NO₂RR coupling reaction.The experimental results show that the Te-Pd NCs has high Faraday efficiency of urea and N atom utilization in coupling catalytic reaction.Through a series of controlled experiments and theoretical calculations,we found that in the Te doped structure,the synergistic effect between Te and Pd can significantly promote CO₂RR to produce^*CO,NO₂RR to^*NH₂,and the combination of^*CO and^*NH₂ to produce urea.（4）We have developed a general cation exchange（CE）strategy for the direct synthesis of noble-metal tellurium-based nanomaterials.2D Pd/Pt/Rh/Ru/Ag/Au-Te nanosheets were prepared by using 2D CuTe nanosheets as starting materials and exchanging with corresponding noble metal ions in suitable solvents.When ethylene glycol and dimethyl sulfoxide are used as solvents,2D Pd₂₀Te₇ and 2D PdTe nanosheets can be obtained,respectively.Further theoretical calculations show that this phenomenon is mainly contributed to the strong interaction between the acyl groups in solvent molecules and Pd cations in solution.Similarly,0D/1D/3D Pd₂₀Te₇ nanocrystals and 0D/1D/3D PdTe nanocrystals can also be prepared by using 0D/1D/3D CuTe nanocrystals with highly controllable morphology as template materials.In addition,based on 2D CuSe nanocrystals and 2D Cu₇S₄ nanocrystals as template materials,the CE strategy is also suitable for the preparation of Pd-Se and Pd-S nanocrystals.