Controllable Fabrication Of Two-dimensional Metallic Materials And Their Electrocatalytic Properties

In heterocatalysis,high-performed catalysts are expected to have hight density as well as activity of catalytic sites.These requirements can be exactly met by two-dimensional(2D)materials which have ultra-high surface area and distinctive electronic structure.Therefore,developing 2D materials as catalysts becomes one of the most promising research directions in the field of 2D materials.Considering the irreplaceable roles of metal elements(especially noble metals)in heterocatalysis,2D metallic materials gain more attention of researchers rather than other catalytic 2D materials.In this thesis,the synthetic approaches,compositional and structural optimization strategies and the structure-property relationships in catalytic reaction of 2D metallic materials are all involved.We focused on several 2D metallic materials with varied surficial composition,surficial structures and dimension,and investigated their electrocatalytic performance in the electrode reactions of fuel cells.Summarize all of the research projects,the main results are listed as follows:(1)We developed a synthetic method for multimetallic Pd@PtM(M=Ni,Rh,Ru)nanoplates including Pd@Pt nanoplates,in which Pt or Pt alloy shells with controlled thickness epitaxially grow on plate-like Pd seeds.The key to achieve high-quality Pt-based multimetallic nanoplates is in situ generation of trace amount of CO tIhrough interfacial catalytic reactions associated with Pd nanoplates and benzyl alcohol.The Pd@PtNi nanoplates exhibited substantially improved activity and stability for methanol oxidation reaction compared to the Pd@Pt nanoplates and commercial Pt catalysts due to the advantages arising from plate-like,core-shell and surface alloyed structures.(2)We developed a controllable etching approach to tailor the fractal dimensions and edge sites of Pd nanosheets and investigated the edge sites in these 2D nanostructures from both structural and chemical aspects.The as-tailored 2D Pd nanostructures with extra edge sites exhibited substantially enhanced electrocatalytic performance for formic acid oxidation reaction,revealing that the specific activities for the edge sites in the 2D nanostructures far exceeded the activities for the low-index planes of Pd.(3)We developed a synthetic method for multimetallic Pd@PtM(M=Rli,Ni,Cu,Pd)nanorings with PtM alloys on surface.We investigated the crystal growth mechanism and found out that the key to achieve multimetallic core-shell nanorings is in situ generation of large amount of CO and benzoic acid through interfacial catalytic reactions associated with Pd nanoplates and benzaldehyde.The Pd@PtRh and Pd@PtNi nanorings exhibited substantially improved activity for ethanol and methanol oxidation reaction compared to the nanoplates with same surficial compositions and commercial Pt/C catalysts,respectively.(4)We developed a simple approach to assembly 2D metallic materials(e.g.Pd or Rh nanosheets)into three-dimensional(3D)aerogels with average size in centimeter scale and controllable shapes.The surficial wettability and mechanical property of these aerogel can be altered with the addition of different cements and reinforcing phases.In the oxygen reduction reaction test without intensified diffusion.Pd aerogels composed of nanosheets could work as both catalysts and gas diffusion electrodes,whose catalytic performance greatly exceeded the performance of Pd black and Pt black loaded on carbon cloth.