Research On Controllable Preparation,physical Properties Regulation And Field Effect Of Platinum-Based Multi-element Nanoalloys

To actively respond to severe challenges such as increasing energy scarcity and environmental pollution,developing more advanced technologies to achieve carbon neutrality is the only way to sustainable development.The research shows that electrochemistry has higher energy conversion efficiency than traditional chemical industry.Green renewable energy based on electrochemistry provides a vast platform for realizing the new industrial technology innovation of low carbon and energy consumption.Due to their high-efficiency energy conversion rate,environmental friendliness,and portability,direct methanol fuel cells(DMFC)have emerged as one of the most absorbing and promising fuel cells with noble metaldominated catalysts at their core,such as commercial platinum-carbon(Pt/C)and platinum-ruthenium-black(PtRu/C).However,the existing Pt-based catalysts still face huge development bottlenecks,such as low energy efficiency,high cost,resource shortage,and ease of poisoning by CO-like intermediates.Therefore,improving the activity of Pt-based catalysts and reducing the cost are the key tasks in the development of DMFC.Using external fields such as magnetic,thermal,and electric fields to regulate electrocatalytic behavior is a promising method to expand the theory,design and synthesis of existing catalysts and fuel cells.Herein,this thesis takes low-dimensional magnetic Pt-based multi-element alloy nanomaterials as the research object,and the research is conducted from three aspects(material synthesis,structure characterization and performance characterization)to explore the phenomena and potential mechanism of multi-field(magnetic field,thermal field)enhancement for methanol oxidation reaction(MOR).The specific research content and innovation results are summarized as follows:(1)CoPt truncated octahedral nanoparticles(CoPt TONPs)with adjustable components were synthesized by hydrothermal method.The effects of external magnetic field and thermal field on MOR properties of room-temperature ferromagnetic CoPt nanoparticles were systematically studied by combining experimental and theoretical calculations.For Co42Pt58 TONPs,the catalytic performance in MOR is greatly increased to the maximum of 14.1%by applying a magnetic field up to 3000 Oe,and it shows a monotonical increase with increasing working temperature.The magnetic enhanced effect is closely related to the Co content of CoxPt100-x TONPs.In addition,the catalytic enhancement effect of CoPtAnnealed annealed at 650℃ was more obvious under the action of the magnetic field,with the highest increase of 25.1%.First-principles calculation points out that the magnetic fields can facilitate the dehydrogenation of both methanol and water by suppression of entropy of the electron spin and lowering of the activation barrier,where OHad intermediates on Co sites plays a more important role.The application of magnetic fields together with thermal fields in MOR provides a new approach to manipulate the performance of DMFC,which will accelerate their potential applications.(2)The effects of applied magnetic field and thermal field on MOR properties of magnetic NiPt polyhedral nano-catalysts were systematically studied for the asprepared and annealed NiPt alloy nanomaterials without room temperature ferromagnetism.The results showed that the MOR activity of NixPt100-x-Annealed annealed at 500℃ could be significantly improved by applying a magnetic field.When the magnetic field intensity varies from 0 Oe to 5000 Oe,the peak current density of Ni68Pt32-Annealed can be enhanced by up to 36.4%.The MOR effect of magnetic enhancement is closely related to the Ni content of NixP100-x-Annealed.However,the magnetic field has no obvious catalytic enhancement effect on the asprepared NixPt100-x nanoparticles.In addition,the MOR activity of NixPt100-x and NixPt100-x-Annealed increased monotonically with the increase in operating temperature.This work provides a new inspiration for the rational design of highly efficient DMFC electrocatalytic systems with magnetic adjustable Pt-based nanocatalysts.(3)Alloy nanomaterials used as efficient fuel cell catalysts have raised significant concern and research because of the particular configurable superiorities and the electronic effects triggered by alloying different metals at the nanoscale.Ternary CuCoPt nanoparticles with tunable composition assembled from polyhedra were synthesized by a simple one-pot solvothermal method and used as highefficient anode electrocatalysts for MOR.The magnetic properties of the CuCoPt nanoparticles were attenuated by increasing Cu content in the alloy.At room temperature and in acidic media,Cu37CO3Pt60 exhibited the best MOR catalytic performance with specific activity and mass activity of 1.26 mA cm-2pt and 4.00 A mg-1Pt,respectively,which were 15.75 and 3.67 times higher than those of commercial Pt/C.The durability test showed that the catalyst was highly stable.Structural characterization indicates that the enhanced MOR catalytic performance of the ternary CuCoPt nanoparticles is mainly due to a combination of a high density of surface active sites,downshifting of the d-band center of the metal Pt,interatomic ligand effects,strain effects,and synergistic effects.This work provides a new idea for the development of multicomponent Pt-based nanoalloy catalysts with adjustable magnetic and structure.