Controlled Synthesis And Electrochemical Catalysis Performance Study Of Pt-based 1D Nanostructures

Due to increasingly severe environmental pollution and prominent energy crisis,the search for substitutes of new and environmentally-friendly fossil fuels cannot be delayed.As an energy conversion device,proton membrane fuel cells have been widely considered as the new energy substitution because of many advantages,such as efficiency,stability and safety.In fuel cells,the efficiency of oxygen reduction reaction at the negative pole determines the overall efficiency of cells.Currently,Pt nanocrystalline catalyst is generated by loading 2-5 nm Pt nano particles to substratum.Except for high price and scarcity of commercial catalysts,catalytic activity and durability are also less than satisfactory.Hence,it has become a key issue to design and generate catalysts with better chemical performance in this field.As for preparing Pt-based ORR nano catalysts,the following methods are adopted to enhance the rate of atom utilization:reducing catalyst particle volume,producing catalysts with base metal precious metal nucleus shell structures,and catalysts with hollow structures.In addition,another approach of optimizing the binding energy between oxygenous substance and catalyst surface is carried out through following steps:alloying,adjust catalyst surface stress and exposing crystal surfaces.Insufficient stability of Pt-based catalyst is mainly ascribed to the following reason:inherent structures,relied by high-quality chemical activity,cannot exist stably from the perspective of thermodynamics.For this reason,high-quality chemical activity and favorable stability cannot be achieved at the same time.In fact,it is also feasible to improve the long-term stability of Pt-based catalyst at negative pole,in order to reduce the cost of PEMFCs.For example,Pt nanowire with 1D structures shows better stability than OD contrast sample of ORR,which can be explained by asymmetrical structures suppressing the ripening process of nano materials.It is also related to increasing interaction by more contact area between nanowire and carbon loading.Based on the synthesis of colloidal nanoparticles,This dissertation proposes an improved,simple and efficient one-step synthesis method of producing 1D nanowire,and conducts systematic study on synthesis mechanism.Meanwhile,based on synthetic Pt nanowire,we also synthesized ORR catalyst with excellent performance.This dissertation mainly discusses the following aspects:1.We introduced a method of using long chain surfactant molecules as soft templates,effectively synthesizing and preparing Pt nanowires in Chap 2.As for this method,Pt nanowire is only 2 nm wide with ultrathin structures.Benefited by high atom utilization and electronic transmission,Pt nanowires shows more superior performance than commercial Pt/C catalyst in oxygen reduction.2.Based on Pt nanowire,we alloyed the nanowire and generated a different type of Pt-M nanowires in Chap 3 and Chap 4.For PtNi ultrathin nanowires,alloyed Ni elements enhanced binding energy between catalyst and oxygen.Besides,small atomic radius of Ni also increased the performance of catalyst.In Rh doped Pt ultrathin nanowires,small amount of Rh improved stability of catalyst.According to experiment and computational simulation of oxygen reduction reaction,Rh took the place of Pt in dissolving out catalyst,thus preventing the damage of catalyst structures.Meanwhile,Rh also enhanced the vacancy formation energy of Pt in this material.Thus,catalyst atoms could hardly be separated out during the catalytic process.3.Considering the above discussion and analysis,we designed a type of PtNiRh trimetallic nanowire catalyst with various advantages,such as the atomic-scale diameter,optimum elementary composition ratio,one-dimensional nano structures of anisotropy in Chap 5.Because of these advantages,compared with Pt/C catalyst,1 nm-thickness PtNiRh trimetallic nanowire/C catalyst demonstrated better chemical activity and stability in ORR.Favorable electronic structures are achieved by adding optimum compositions Ni and Rh with superb and activity {111} surface layer.Hence,geometric and ligand effects are combined to improve intrinsic activity of catalyst.In addition,by maximizing the utilization efficiency Pt atoms,atomic-scale diameter can enhance the mass activity.Besides,one-dimensional anisotropy structures and Rh atoms greatly enhance catalytic stability by improving catalyst structures and compositional stability.