Controlled Synthesis Of Platinum-based Nanomaterials And Their Electrocatalytic Performances

Noble metal nanomaterials,as the most active branch in the field of nanoscience,exhibit excellent optical,electronic,and catalytic properties.Combining the unique physicochemical properties of noble metals with the special performances of nanomaterials,noble metal nanomaterials have bright application prospects in optics,electrics,biology,energy and catalysis fields,which have attracted high attentions and extensive studies of scientific workers.A large number of researches show that the unique properties of noble metal nanomaterials are closely related to many factors,such as size,composition,morphology,facet,dimensionality,surface structure and so on.While the practical applications of noble metal nanomaterials need to be based on the well-controlled syntheses of their microstructures and the accurate analyses of their growth mechanisms.Therefore,the rational design and development of synthetic methods and strategies for precisely controlling their morphologies and nanostructures,shall provide favourable theoretical guidances and experimental bases for the practical applications of noble metal nanomaterials,and these studies have very important value and significance.As an important member in the field of materials science,noble metal nanomaterials possess the features of large specific surface area,high surface atoms occupancy,highly unsaturated coordination of surface atoms and so forth.These features greatly improve the inherent catalytic activity and chemical reactivity of noble metal nanomaterials,enabling them with the unique catalytic performances that the corresponding bulk materials are not available.Among various noble metal nanomaterials with high catalytic performances,platinum?Pt?-based nanomaterials are undoubtedly the most dazzling pearls.Pt itself exhibits large ductility,highly thermal and electrical conductivity,superior chemical stability and excellent catalytic activity,and it is a very suitable metal material as the catalyst.Pt-based nanomaterials therefore become a class of high-performance electrocatalyst in fuel cells.This doctoral dissertation mainly focuses on exploring the synthetic strategy for precisely controlling the morphologies and nanostructures of noble metals,in order to obtain the Pt-based nanomaterials with clean surface,unique structure,and high catalytic performance.The microstructure,formation factor,and growth mechanism of the as-obtained Pt-based nanomaterials were systematically investigated and studied by us,and their catalytic performances in fuel cell reactions were emphatically studied with the aid of electrochemical technology.In addition,we analyzed the corresponding relationship between the structure and performance of Pt-based nanomaterials in depth by means of the density functional theory in quantum mechanics.The main research content and conclusions are summarized as follows:Chapter 1.We introduced the research background of noble metal nanomaterials in brief,and summarized the recent progresses in the properties,synthesis,and applications of Pt-based nanomaterials.The topic basis and main research project of this doctoral dissertation were also demonstrated.Chapter 2.We explored a novel and reliable synthesis strategy of wet chemical reduction.High quality Pt nanowires and Pt octahedra were selectively synthesized.They exhibit different shapes and dimensions,but the same exposed crystal facet of{111}.The research results showed that Pt nanowires with one-dimensional structure,minimized edges and corners nanostructure can be used as an excellent electrochemical catalyst.Chapter 3.Based on the novel synthesis method explored previously,we developed and synthesized a series of binary and ternary Pt-based alloy nanowires,including the Pt-Ni nanowires.This study not only successfully achieves the general production of one-dimensional multicomponent Pt-based alloy nanostructures,but also provides a powerful platform for the preparation and application of high-performance nanocatalysts.Due to the unique one-dimensional nanostructure and a high density of low-coordinate atomic steps,such as{211}and{311}steps,the as-prepared Pt₃Ni alloy nanowires with high yield exhibit excellent catalytic activity and stability in the oxygen reduction reaction,making them among the most active electrocatalysts ever achieved in PtNi-based nanocatalysts toward the oxygen reduction reaction reported to date.Chapter 4.We deeply studied the Pt-Co alloy nanowires with controllable hierarchy and periodic uneven surface.The detailed researches show that the surface of the single crystalline nanowires has a Pt-rich nanostructure and large-density high-index facets of{310}.Due to the comprehensive influences from high surface area,alloy effect,one-dimensional morphology,ordered intermetallic nanostructure,high-density high-index facets factors and so forth,the as-synthesized Pt-Co alloy nanowires exhibit super-high catalytic activity and excellent durability in the oxygen reduction and alcohol oxidation reactions,making this class of catalyst the most active and stable electrocatalyst ever achieved in PtCo-based alloy nanomaterials reported to date to the best of our knowledge.Pt-Co alloy nanowires are expected to apply as the high-performance nanocatalyst in the future practical proton exchange membrane fuel cells.This study shows extremely important value and significance for precisely controlling the surface structures of one-dimensional Pt-based nanomaterials,designing the high-index facets and ordered intermetallic nanostructures,and thus realizing the effective control for the catalytic performance of nanomaterials.Chapter 5.For the first time,we synthesized the high yield PtPb/Pt core/shell hexagonal nanoplates integrating the tensile strain and compressive strain by using a facile wet-chemical strategy.This study is the first report with large-scale synthesis of two-dimensional Pt-based core/shell nanomaterials up to now.The as-synthesized PtPb hexagonal nanoplates have unique nanostructure,that is,the core exhibits the ordered PtPb intermetallic nanostructure with a hexagonal phase,and the shell consists of four to six Pt atomic layers with a cubic phase.Owing to the very high tensile strain of Pt?110?planes located outside the nanoplates,thin two-dimensional morphology,and the ordered PtPb intermetallic phase,the as-prepared PtPb/Pt core/shell hexagonal nanoplates can deliver excellent catalytic activity and outstanding catalytic stability in the oxygen reduction and alcohol oxidation reactions,making the new class of nanomaterial among the high-performance nanocatalysts in fuel cells.This study not only addresses the difficulties in obtaining two-dimensional Pt-based nanomaterials due to the strong anisotropy existed in synthetic methods for a long time,but also opens up a new way for the preparation and application of high-performance two-dimensional Pt-based nanomaterials.