Study On Construction Of High-efficiency Platinum-based Catalyst And Their Application In Oxygen Reduction Reaction

In order to alleviate the environmental degradation and energy crisis caused by excessive consumption of fossil fuels,modern industry has an urgent demand for the supply of new generation of renewable energy.In this regard,the proton exchange membrane fuel cells（PEMFCs）is considered one of the most promising energy conversion systems in the next generation of energy technology revolution because of its high-efficiency,zero-carbon emissions.However,due to the lack of effective and durable electrocatalysts,the advances of PEMFCs technology are still severely hampered by the slow kinetics of the oxygen reduction reaction（ORR）at the cathode.Among numerous viable catalysts,Pt-based catalysts have long been regarded as the most promising catalysts to boost the ORR,yet the scarcity,high cost and poor durability of Pt further hinder their scale-up applications.Therefore,the development of Pt-based catalysts that can fully improve the utilization efficiency,catalytic activity and long-term durability of Pt for ORR is crucial to the commercial viability of PEMFCs.In order to improve the catalytic performance and utilization of Pt,this paper focuses on the design and synthesis of new and efficient Pt-based composite catalyst.On the one hand,we mainly start with rational selection and controlled preparation of the catalyst supports for Pt nanoparticles.By precisely controlling the morphology of catalyst support material and the contact facet between the catalyst support material and Pt,the significance of facet-coupling effects on ORR is elaborated combining experimental observation with DFT theoretical calculation.On the other hand,the urchin-like peapoded core-shell-structured Ni Co₂@Pt/C composite catalyst is synthesized by means of morphology optimization and surface control.The active materials encapsulated in porous carbon films present a good dispersibility,which can effectively avoid the migration and agglomeration of active nanoparticles during the catalytic process.Thus,the catalytic activity and stability of the prepared Ni Co₂@Pt/C catalyst are significantly improved.The specific research contents of this topic are as follows:1)First,we synthesized Sc-Li Ti O₂ nanooctahedra by a simple one-step hydrothermal method.As demonstrated by scanning electron microscopy and high-resolution transmission electron microscopy,the synthesized Sc-Li Ti O₂ has regular octahedral structure and smooth surface,as well as good single crystal properties and{111}facet exposure.Then,the Pt NPs are deposited on the Sc-Li Ti O₂ surfaces using the thermal reduction method,followed by annealing treatment at a low temperature.The results show that the Pt{111}crystal facets can achieve atomic-level contact with the highly the lattice-matched Sc-Li Ti O₂{111}crystal facets to form a specific facet-coupling heterostructure,leading to strong cooperative effects between the Sc-Li Ti O₂ and the Pt as well as the epitaxial growth and favorable exposed facets of Pt on the surface of Sc-Li Ti O₂.These key features endow Pt NPs/Sc-Li Ti O₂ with a mass activity of 1.44 A mg_Pt^-1 and specific activity of 1.78 m A cm^-2,which are 8.0 and7.1-fold higher than those of the state-of-the-art Pt/C,respectively.Meanwhile,it can undergo 20000 sweep cycles with negligible activity decay and no obvious changes in morphology or composition,showing excellent ORR durability.Thus,this work well addresses the common problems of low activity and poor stability of Pt/support composite catalysts.2)The urchin-like peapoded core-shell-structured Ni Co₂@Pt/C composite catalyst is prepared by simple wet-chemical method and two-step annealing method,in which the Ni Co₂ alloy is as the core while Pt layer as the shell to form the Ni Co₂@Pt nanoparticles encapsulated in porous carbon film.This unique structure endows Ni Co₂@Pt/C catalyst with many merits,such as porous structure,high electrical conductivity,abundant active sites and large specific surface area.More importantly,by combining the synergistic interaction between Ni Co₂ core and Pt layer with the advantages of embedded structure,the Ni Co₂@Pt/C catalyst exhibits much higher ORR activity and durability than commercial Pt/C.