Synthesis and Electrocatalysis of ternary shape-controlled octahedral Pt alloy Nano catalysts for the Oxygen Reduction Reaction

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The electrocatalytic reduction of molecular oxygen (oxygen reduction reaction, ORR) is an electrode process of great significance for metal air batteries and hydrogen fuel cells. Even on Pt surfaces, the ORR is a sluggish interfacial reaction. New Low-Pt ORR catalyst concepts are needed with enhanced intrinsic reactivity and high stability. Pt alloy single crystal-based catalyst studies predicted PtNi bimetallic octahedrally-shaped nanocatalysts as a favorable group of nanostructured particle ORR catalysts. However, electrocatalyst research involving PtNi octahedral nanoparticles largely focused on small (5-9 nm edge length) and Pt-rich nano-octahedral catalysts, which unfolded only about a tenth of their predicted intrinsic reactivity in fuel cell membrane electrode assembles (MEAs). This project will address this challenge and will investigate new tunable synthetic strategies toward octahedral Pt alloy nanoparticles of a much wider size range than that accessible today. Following our underlying hypothesis, octahedrally shaped particles of this size range will fully unfold their theoretically predicted catalytic ORR reactivity in thick realistic electrode layers.The goal of this project is to establish previously inaccessible structure-size-reactivity relationships of multi-metallic Pt alloy octahedral nanocatalysts for the ORR. Specific objectives include the discovery of new synthetic pathways with precise and tunable control over the resulting alloy particle and facet size and overall composition. Of particular interest is the size regime above 30 nm that is predicted to show particularly high intrinsic catalytic reactivities, which will benefit the resulting oxygen electrode layer performance. The project work will cover previously described bimetallic PtNi reference catalysts, yet will focus on new synthetic procedures resulting in well-defined tri-metallic PtNi-M (M=Mo and other transition metals) octahedral nanocatalysts. Synthesis will be followed by physico-chemical and electrochemical characterizations to establish structure-function correlations. Promising ternary Pt nano-octahedra will be supported on porous carbon supports with varying pore structure enabling the controlled accommodation of the large nano octahedra both inside accessible pores and on the outside surface of the primary and secondary carbon structure. These supported octahedral catalysts will be subject to electrochemical activity testing in thin film as well as thick-film electrodes of Membrane Electrode Assemblies in single PEM fuel cells.