Controllable Synthesis Of Pt-Based Nanocrystalline Electro-Catalytst And Catalytic Performance

Energy and environmental issues are major problems faced by the current human society,because of the limited reserves,the excessive exploitation of fossil fuels and the unilateral pursuing on the economic development but ignoring many of the environmental protection problems in the past hundred years,which has brought serious impact to the environment and hindered the development of society seriously.Therefore,developing environmental-friendly new energy and improving energy efficiency has become a hot topic about sustainable development.As the most important of a new energy,fuel cell have been wildly used due to its high energy efficiency,low operating temperature and portable pollution-free battery appeared in people's field of vision.Especially,the direct methanol fuel cell(DMFC)has attracted much attention due to its small size and easy to carry,high conversion efficiency,cheap raw materials and product almost green pollution-free advantages.Since the advent of direct methanol fuel cell technology,it keeps the research heat until now,it is widely believed that this technology has good application prospect,over time,it can be widely used.A large number of studies show,platinum is a precious metal with excellent catalytic and electrical properties,and it has been widely employed in chemical,petrochemical,pharmaceutical,electronic and automotive industries.Pt-based catalysts are the main catalysts in direct methanol fuel cells(DMFCs)currently,it has been used in DMFC anode methanol oxidation and cathodic oxygen reduction reaction.However,Pt metal is not only a small amount of reserves,expensive,and Pt anode catalyst CO poisoning and other surface adsorption problems,affecting the catalyst activity and stability.At the same time,its internal electrochemistry and mass transfer mechanism is not clear and other factors have restricted its development.Therefore,developing Pt catalyst replacement and preparation of Pt-based catalyst with low content of platinum,improving the activity stability of the catalytic materials is a priority,in order to get more excellent Pt catalysts,transition metal is indispensable,such as Ni,Co,Sn,Cu,Fe,etc.to reduce the cost,so as to promote the large-scale commercialization of fuel cells.Based on the above research background,the controllability structure of Pt-transition metal Cu and Fe alloy nanocrystalline fuel cell catalyst and its electrocatalytic performance for methanol oxidation and oxygen reduction were studied in this paper.The first chapter is introduction.In this chapter,we summarizes the development history,classification and basic principle of fuel cell firstly,and then elaborates from the advantages,principles,development status and bottleneck of development of DMFC.Finally,The classification of anodic electrocatalyst is discussed.Based on the advantages of Pt-based alloy catalyst,we have developed the research direction and focus,and designed the experimental scheme.In the second chapter,DMF was used as the solvent,PVP and NaBr as the morphological control agent,and Pt(acac)2 and Cu(acac)2 were used as precursors,by changing the reducing agent of glycine,formaldehyde,hydrazine hydrate,ascorbic acid and sodium borohydride,a series of well-dispersed bimetallic PtCu and Cu@PtCu core-shell bimetallic nanocrystalline catalysts with different sizes and topography were fabricated by a simple solvent thermal method.The phase,structure,size,morphology and surface properties of PtCu and Cu@PtCu bimetallic catalysts were investigated by controlling the ratio of precursors,reducing agent type,reaction time and temperature,solvent type and surfactant type.These catalysts with spherical and tetrahedral,octahedral,twig-like and core-shell structures were prepared and we have systematically studied the catalytic performance of PtCu and Cu@PtCu alloy nanocrystalline catalysts for the electrocatalytic oxidation of methanol.The experiments confirmed that the electrocatalytic properties of PtCu and Cu@PtCu nanocrystalline catalysts have a great dependence on their structure,morphology,size and surface properties.Among them,Cu@PtCu bimetallic alloy nanocrystalline catalyst has a unique core-shell structure,so that the Cu core can effectively transfer electrons to the PtCu shell,and because DMF and PVP contain N elements,in the synthesis process in situ to achieve Cu@PtCu bimetallic alloy nanocrystalline surface of the highly active N species of doping,and thus greatly enhance the catalytic activity of Cu@PtCu bimetallic alloy nanocrystalline catalyst for the methanol oxidation reaction.What's more,its electrochemical activity is up to 1568 fmA cm-2,which is 7.1 times(221 mA cm-2)of commercial Pt/C catalyst,which shows excellent methanol oxidation activity and stability.In the third chapter,based on the research of PtCu and Cu @ PtCu bimetallic alloy nanocrystalline catalysts,we preparated a three metal alloy nanocrystalline catalysts by the incorporation of the third metal in order to further enhance the catalytic activity and stability of the catalyst for the methanol oxidation and oxygen reduction reaction,and to achieve a catalyst with excellent dual-function catalytic properties for the methanol oxidation reaction and oxygen reduction reaction at the same time.Based on the synthesis conditions of PtCu and Cu@PtCu bimetallic alloy nanocrystalline catalysts,Pt(acac)2,Cu(acac)2 and Fe(acac)3 were used as precursors.By adjusting the reactant precursor the PtFeCu three metal alloy nanocrystalline catalyst was successfully prepared and the bifunctional catalytic properties of the methanol oxidation reaction and oxygen reduction reaction were studied in detail.The results show that compared with PtCu and Cu @ PtCu bimetallic alloy nanocrystalline catalyst,the catalytic performance of PtFeCu three metal alloy nanocrystalline catalyst on the methanol oxidation reaction is improved.This is mainly due to the synergistic effect of Pt-Fe in the catalyst,which reduces the Pt-CO bond binding energy and leads to the oxidation of CO more easily,thus improving the stability and activity of the catalyst.At the same time,the catalyst also has a better catalytic activity for oxygen reduction,and its half-wave potential reaches 0.83V in 0.5M H2SO4 solution,which is superior to most of the similar catalysts reported in the literature,and successfully achieves bifunctional catalytic properties.Although there are many electrocatalysts with high catalytic activity for methanol oxidation or oxygen reduction reactions,it is rare to report on bifunctional catalysts with high catalytic activity for both catalytic reactions.Therefore,the PtFeCu three metal alloy nanocrystalline catalyst will have a good application prospect in the field of fuel cell.The fourth charpter is the summary and prospect of the thesis,and the unfinished research work and future research was discussed to provide guidance for future research.