Dr. Young-Uk Kwon
Professor, School of Material Science and Engineering, Tianjin Polytechnic University, China.

Speech title: Syntheses and characterization of transition metal core and platinum shell nanoparticles for electrocatalysts

Abstract: One of the most urgent issues to be addressed for the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) to be realized is the high cost of and low stability of the electrocatalysts. Until present time, Pt is the most heavily used element for PEMFC electrocatalysts for its superiority in efficiency and durability to other elements, hence the high cost problem of electrocatalyst. Alloying with a transition metal has been predicted to enhance the catalysis performance of Pt theoretically, which has been proven by many experimental data. It also is an effective way to reduce the use of expensive Pt. M@Pt core-shell nanoparticles (NPs) with a transition metal (M) in the core and Pt in the shell is expected to be even better because they allow the most efficient way to utilize Pt, which point also has been supported by experiments. Despite all these advantages, the complexity involved in forming core-shell NPs hinders the further progress in this direction. In this regard, our group has developed a simple one-step synthesis procedure to form M@Pt NPs with various transition metals such as Mn, Fe, Co, and Ni. The product NPs are uniform in size of 2-3 nm. The core-shell structure of these NPs was proven by a number of means, including the structural refinement in which the coordinate of each atom of the model NP can be determined. In certain systems such as M = Mn and Fe, the Pt shell thickness was controlled from 1 monolayer (ML) to 2 ML. This method could be extended to ternary systems such as (Pd,Co)@Pt and Fe@(Pt,Ru). All of the core-shell NPs mentioned show improved catalytic performance and durability from those of commercial Pt/C electrocatalyst. The syntheses are achieved by sonochemical reactions in a polyol medium, ethylene glycol being the most efficient, on metal acetylacetonate complexes as the reagents (M(acac)n, n = 2 or 3; Pt(acac)2). The effects of a number of synthesis parameters such as the reagent composition, type of solvent, temperature, and others were systematically varied. Based on the results we propose a mechanism for the formation of M@Pt core-shell NPs.