Pd-Sn金属间化合物纳米单晶的可控合成、氧气还原电催化性能及机理研究

The widespread deployment of low-temperature fuel cell technologies requires superior oxygen reduction catalysts. Ordered intermetallics of Pt-group metals with other cubic-closed packed metals have the best catalytic activity so far, but current synthetic routes require high temperature annealing (usually above 700 °C) to convert disordered alloy particles to ordered intermetallic structures. To attain highly active ORR catalysts, we need to develop a flexible method for preparing ordered intermetallic nanoparticles at low temperatures, which will allow us to control the size and shape. In this project, we propose that by utilizing a low melting point metal with a crystal structure that is not FCC, we can reproducibly prepare Pd-based ordered intermetallics in various reaction conditions. .To understand the nature of high catalytic performance we are interested in identifying the structure and composition of surface activated PdSn2. We will also propose a mechanistic pathway for ORR on PdSn2 by utilizing operando spectroscopic methods, and electro-kinetics. In addition to this we are exploring routes to control the size, shape, and crystal structure of ordered intermetallic nanoparticles, because it is well known that these parameters are critical for controlling the chemical reactivity and stability of a nanoparticle electrocatalyst. The plan laid out in this proposal provides a method for preparing ordered intermetallic catalysts with well-defined structure, allowing one to systematically interrogate structure-property relationships. The established research metrics can easily be extended to other reactions, setting the stage for a long-term program on understanding the influence of surface structure in electrochemical catalysis.

低温燃料电池的大规模应用需要性能更优异的氧气还原催化剂。铂族贵金属的金属间化合物是已知的活性最高的材料，但是目前需要通过高温退火制备。开发金属间化合物的低温制备方法可以实现对其形貌和尺寸的调控，具有重要的科学意义。在本项目中，我们首先利用低熔点、非立方晶格的非贵金属元素锡与钯合金化，可以实现一步液相低温合成PdSn2的单晶金属间化合物纳米颗粒。通过深入表征PdSn2的表面微观结构和活化过程，结合电动力学实验、热力学参数测定、实时实空间光谱表征和理论模拟计算，探讨氧气在PdSn2表面发生的一系列变化，理解氧气分子吸附活化的步骤和活性位点的分布，在分子或原子层面总结归纳材料性质与结构的关系，以此指导新材料的理性设计与合成，改善贵金属合金ORR催化剂易燃料中毒的问题，为制备性能优异的ORR催化剂用于新一代燃料电池的阴极材料提供新思路。

无机物纳米材料结构的理性设计和可控合成是确保其实际应用发挥最大性能的关键。在异相催化领域，催化剂表界面原子结构很大程度上决定了底物分子在表面的吸附能，从而直接确定了催化反应的最优路径，影响最终反应的活性和选择性。如何发展新的合成方法以实现对特定表界面结构的可控构建，是纳米异相催化剂制备的难题。在本项研究中，结合液相合成和固相合成技术，通过构建核壳结构、二维结构、非晶结构等特殊的表界面原子构型，深入研究了纳米催化剂在光催化染料降解、电催化吸氢、二氧化碳电催化还原、苯乙炔热催化加氢等多种异相催化反应中构效关系，证实了该研究思路的普适性，制备合成了一系列高活性高选择性兼具的催化剂，为异相催化活性材料设计提供了新的思路和方向。