Preparation And Properties Of Platinum-based Catalysts

Developing clean energy and energy conversion devices is imminent due to energy crisis and environmental deterioration.Proton exchange membrane fuel cell（PEMFC）is considered as a potential energy conversion system with high efficiency and environmental friendliness.However,its performance is limited by the slow kinetics of cathodic oxygen reduction reaction（ORR）.This thesis is guided by basic electrochemistry,electrocatalysis,chemical kinetics and thermodynamics,aiming at the key scientific problems existing in Pt-based ORR catalysts.we used solid-state phase transition strategy and heat treatment（the main post-treatment）to design catalyst structure and interface.The structural and interfacial effect result from controlling experimental parameters have a beneficial impact on the preparation of Pt based catalysts with high activity and high stability.The main innovation research of this dissertation is as follows:（1）Carbon supported platinum tin oxide hybrid catalyst（Pt–Sn O₂/C）with strong coupling interface was prepared by simple dealloying phase separation method.A strong coupling effect existed in the catalyst interface with the Pt（111）and Sn O₂（200）planes overlap along the vertical direction.Electrochemical tests showed that the Pt–Sn O₂/C catalyst had excellent activity and stability for catalytic and good performance in MEA.The excellent performance was attributed to the strong coupling effect at the interface,which was not only conducive to enriching more electrons,but also had a better compressive strain effect on the Pt surface.Meanwhile,the stable Pt-Sn O₂-C three phase structure contributed to anchor Pt particle,strongly.In addition,the catalyst exhibited strong reactive oxygen species degradation ability.This phase separation method is expected to be applied to the preparation of other strongly coupled interface nanohybrid materials,and provides guidance for the high performance heterogeneous catalysts in low-cost energy conversion devices.（2）Based on the strategy of ordering and surface treatment,carbon-supported platinum iron alloy nanoparticles with small size were prepared by modified microwave-assisted alcohol reduction method.Subsequently,L1₀platinum iron intermetallic was obtained by phase transformation during the heat treatment.Further,carbon supported platinum-iron@platinum-bismuth intermetallic compound catalyst（Fe Pt@Pt Bi）with a core-shell structure and enhanced surface compressive strain was obtained by adopting the leaching-intercalating-rearrangement method.The Fe Pt@Pt Bi catalyst exhibited excellent ORR performance and good function in MEA,which attributed to the superimposed compressive strain of the Pt surface due to in-plane shearing resulting from the presence of the large Bi atoms in the surface structured Pt Bi overlayers.Furthermore,the surface treatment strategy resulted in a series of activity-enhanced catalysts,opening an exciting avenue for the synthesis of novel ORR catalysts with high stability and antitoxicity.（3）Based ont the second-phase-induced structural phase transition strategy,carbon supported platinum nanoparticles seeds were prepared by modified microwave-assisted alcohol reduction method.Subsequently,ordered L1₀platinum cobalt alloy catalyst（L1₀-Co Pt）was obtained during impregnation and heat treatment process.The L1₀-Co Pt catalyst showed excellent ORR activity and stability and good performance in MEA,which attributed to the enhanced strain effect brought by intermetallic compounds.In addition,the synthesis method relied on a mount of vacancies provided by the second phase Co₂P formed during the heat treatment process,which accelerated the diffusion of Pt into the orthogonal cobalt-rich skeleton,realizing the formation of L1₀structure.This second-phase-induced structural phase transition synthesis strategy has great significance for the developing more intermetallic material systems.