| Although the traditional gasoline-fueled cars bring convenience to human,they affect the quality of people's life due to the pollution of exhaust gas.Therefore,the development of clean and environmentally new energy vehicles has become an inevitable trend.The"Made in China 2025"plan issued by the State Council clearly states that"Continue to support the development of electric vehicles and fuel cell vehicles".At the same time,the research institutions and enterprises related to new energy vehicles all over the world have placed the content related to new energy vehicles in an important position.Proton exchange membrane fuel cell(PEMFCs)is a kind of device that transform the chemical energy directly into electric power.Characterized by high energy conversion efficiency and no pollution of reaction products,it has gradually become the first choice technical routes of new energy vehicles.However,the cathode oxygen reduction reaction(ORR)rate of PEMFC is very slow,and platinum,which is scarce and expensive,is needed to improve the reaction rate.As a result,the cost of proton exchange membrane fuel cells is extremely high,which seriously restricts the commercialization process.Therefore,the preparation of high activity,high stability and low-cost oxygen reduction reaction catalysts,which can effectively reduce the cost of catalysts in fuel cells,and has been a research hotspot in recent decades.Based on the platinum cobalt catalyst system,this thesis developed a simple approach for a series of novel platinum-based catalysts.The composition,morphology and crystal structure of nanomaterials have been fully analyzed,and the formation mechanism of carried out detailed analysis and discussion,and the study of the electrocatalytic properties are sufficient.The main research contents of this thesis are summarized as follows:(1)By taking the advantage of grain boundary vulnerability to corrosion,a solvothermal method was proposed to control the synthesis of Pt Co nanorod assemblies with a high activity ratio and a large surface area.In the solvothermal treatment,the Pt Co nanorod assemblies,with ultrafine rounded end short nanorods and high index facets(HIFs),were prepared by selective dissolution of nanoscale grain boundaries of Pt Co nanowire assemblies.This method has a high yield and repeatability,and can be used to synthesize 1 g carbon-supported Pt Co nanorod assemblies in a single batch by simple amplification.The electrochemical specific surface area of Pt Co nanorod assemblies was 48.32 m2/g Pt,and the half-wave potential was 0.924 V.The mass and specific activities of the prepared carbon-supported Pt Co nanorod assemblies were 0.914 A/mg Pt and 1.854 m A/cm2,2.4 and 1.9 times higher than that of Pt Co nanowire assemblies(0.377 A/mgPtand 0.967 m A/cm2),5.7 and 6.2 times higher than that of commercial Pt/C(0.161 A/mgPtand 0.300 m A/cm2),5.9 and 3.6 times higher than that of Pt nanowire assemblies(0.155 A/mgPtand 0.508 m A/cm2).The mass activity of the Pt Co nanorod assemblies at 0.9 V has exceeded the 2020 target(0.44 A/mg Pt)of the United States Department of Energy.Notably,the Pt Co nanorod assemblies exhibited high stability with a loss of mass activity of 25.6%after 10,000 cycles,whereas only 22.3%were lost after 10,000 to 50,000 cycles of accelerated durability test.The ultrahigh durability is attributed to the jagged surfaces of Pt Co nanorod assemblies resulting from surface reconstruction during electrochemical processes.This self-optimization phenomenon may lead to a new type of electrocatalyst with high efficiency and long life.(2)Ultrafine Co(OH)2 nanoparticles with particle size distribution of 3?5 nm were synthesized by the solvothermal method.The prepared ultrafine Co(OH)2 nanoparticles were dispersed on the surface of 3D graphene and annealed at 300?H2/Ar(5%H2)to form Co3O4-Co core-shell nanostructures.Co(OH)2is easily thermolysis into Co3O4,and the surface and the near-surface layer of Co3O4nanoparticles are reduced to metal Co in a reducing atmosphere.Co3O4-Co core-shell nanoparticles were rapidly replaced in a small amount of low concentration H2Pt Cl6 solution to form Co3O4-Pt core-shell nanoparticles.Co3O4-Pt has a diameter distribution of 3.67±1.03 nm,and contains only a small number of atomic Pt shells and presents a nanostructure with high platinum utilization.In addition,3D graphene,as an open structure catalyst carrier,has three-dimensional molecular accessibility and is conducive to mass transfer.The electrochemical specific surface area of Co3O4-Pt@3DG was 46.89m2/g Pt,and the half-wave potential was0.896 V.The mass activity and specific activity of Co3O4-Pt@3DG were 1.018A/mg Pt and 2.170 m A/cm2,respectively,which were 7.6 and 8.1 times higher than that of TKK-Pt/C(0.136 A/mgPt and 0.266 m A/cm2).In addition,Co3O4-Pt@3DG has a high stability,with an initial value loss of about 12.97%after 10,000cycles.The high activity is mainly attributed to the ultrathin core-shell structure and ultrahigh Pt utilization rate,as well as the tensile strain generated by the interaction between the near-surface Co3O4 and the surface Pt shell with appropriate thickness,and the electron transfer between Co and Pt.(3)Ultrafine Co(OH)2 nanoparticles with particle size distribution of 5?7 nm were prepared by increasing the reaction temperature and reaction time of the solvothermal method.The prepared Co(OH)2 were dispersed on the surface of3D graphene and annealed at 400?under a gas mixture(H2/Ar,5%H2).Co(OH)2is easily converted into Co3O4,and the surface and near-surface atomic layers of Co3O4 nanoparticles are reduced to metal Co in the reducing atmosphere,forming a Co3O4-Co core-shell structure.Co3O4-Pt core-shell nanoparticles were prepared by rapid displacement reaction in low concentration H2Pt Cl6 solution.Finally,Co3O4-Pt core-shell nanoparticles were transformed into porous Pt spheres through a slow displacement reaction process.The P-Pt@3DG showed a high ORR activity in acidic electrolytes.The electrochemical specific surface area of Co3O4-Pt@3DG was 55.56 m2/g Pt,and the half-wave potential was 0.922 V.The mass activity and specific activity of P-Pt@3DG were 0.542 A/mg Pt and 0.976 m A/cm2,respectively,which were 4.0 times and 3.7 times higher than that of TKK-Pt/C.In addition,the P-Pt@3DG has high stability,with an initial value loss of only about 5.35%after 10,000 cycles.The porous platinum nanoparticle with an open structure is a kind of ultrahigh Pt utilization rate nanostructure.In addition,the catalyst carrier,3D graphene,exposes 3D transparent nanostructure and graphene-like phases,and provides rapid ion channels to facilitate mass transfer processes,and excellent electrical conductivity and electrochemical stability. |
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