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

分子氧的电催化还原（oxygen reduction reaction， ORR）是对金属空气电池和氢燃料电池具有重要意义的电极过程。即使在铂表面，ORR也是一个缓慢的界面反应。需要新的低铂ORR催化剂概念，以增强固有反应性和高稳定性。Pt合金单晶型催化剂的研究预测了PtNi双金属八面体纳米催化剂是一组有利的纳米结构颗粒ORR催化剂。然而，涉及PtNi八面体纳米粒子的电催化剂研究主要集中在小的（5- 9nm边长）和富含pt的纳米八面体催化剂上，这些催化剂在燃料电池膜电极组装（MEAs）中只展现了其预测的固有反应性的十分之一。该项目将解决这一挑战，并将研究新的可调合成策略，以实现比目前可获得的更大尺寸范围的八面体铂合金纳米颗粒。根据我们的基本假设，这种尺寸范围的八面体颗粒将在厚的现实电极层中充分展现其理论预测的催化ORR反应性。本项目的目标是建立多金属Pt合金八面体纳米催化剂的结构-尺寸-反应性关系。具体目标包括发现新的合成途径，对所得合金颗粒和facet尺寸以及整体成分进行精确和可调的控制。特别令人感兴趣的是30 nm以上的尺寸体系，预计会显示出特别高的内在催化反应活性，这将有利于得到的氧电极层性能。该项目工作将涵盖先前描述的双金属PtNi参考催化剂，但将重点放在新的合成方法上，从而产生定义良好的三金属PtNi-M （M=Mo和其他过渡金属）八面体纳米催化剂。合成之后将进行物理化学和电化学表征，以建立结构-功能的相关性。有前途的三元Pt纳米八面体将被支撑在具有不同孔隙结构的多孔碳载体上，使得大型纳米八面体既可以在可访问的孔隙内，也可以在伯碳结构和仲碳结构的外表面上可控地容纳。这些负载的八面体催化剂将在单个PEM燃料电池的膜电极组件的薄膜和厚膜电极上进行电化学活性测试。

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.