Nanoscale Pt Alloy electrocatalysts with well-defined shapes: Synthesis, Electrochemical Analysis, and ex-situ/in-situ TEM Studies

燃料电池技术的发展对未来的能量转换和存储应用具有重要意义。质子交换膜（PEM）燃料电池作为移动和固定设备的清洁能源正引起人们的特别关注。在不影响活性和长期稳定性的前提下，减少燃料电池中稀有且昂贵的铂作为催化剂材料的用量显得尤为重要。八面体Pt-Ni纳米颗粒作为PEM燃料电池的催化剂表现出优异的性能。然而，这种定型催化剂通常缺乏长期稳定性，例如由于定型损失。它们的电化学活性和稳定性与纳米粒子的合成和合成后处理提供的原子尺度结构密切相关。因此，了解纳米催化剂生长和降解的原子机制对于调整纳米催化剂的性能具有重要意义。在本项目第一期资助期内，我们合成了控制尺寸和表面组成的八面体Pt纳米粒子，并采用不同的合成后方法对其表面结构进行优化，研究了其电化学活性和稳定性，并通过分析电镜监测了催化剂在整个过程中的结构演变。目的是将原子尺度的微观结构演变与它们的电催化活性和长期稳定性联系起来，最终帮助生产更稳定的催化剂。特别是，我们已经举例说明，表面掺杂铑可以大大提高八面体催化剂的形状稳定性和保持较高的活性。我们后续项目提案的总体目标是在多金属电催化剂的微观结构分析和描述方面取得方法和概念上的进展，并结合对其表面化学和表面掺杂形状PtNi纳米颗粒在操作电催化条件下的结构演变的更深入了解。我们将通过探索特定的合成方法对异形合金电催化剂在越来越现实的“原位”和最终“operando”条件下的化学和结构转变的影响来实现这一总体目标。更具体地说，我们将专注于1)系统地研究表面掺杂对结构/组成稳定性的影响，2)原位化学和热合成后处理及其对形貌、结构和组成的影响，3)原位研究反应气体与电催化剂表面的相互作用，最后4)电化学液体电池中电催化剂的原位和操作研究。

Developments in fuel cell technology are of great importance for future energy conversion and storage applications. Proton exchange membrane (PEM) fuel cells are attracting particular interest as clean power sources for mobile and stationary devices. It is especially important to reduce the amount of rare and expensive Pt as catalyst material in the fuel cell without compromising the activity and long-term stability. Octahedral-shaped Pt-Ni nanoparticles have demonstrated an outstanding performance as catalysts for PEM fuel cells. Often, however, such shaped catalysts lack in long term stability, e.g. due to shape-loss. Their electrochemical activity and stability is crucially linked with their atomic-scale structure that is provided by the synthesis and post-synthesis treatment of the nanoparticles. Therefore, it is of high importance to understand the atomic mechanisms of growth and degradation in order to tune the performance of the catalyst nanoparticles. In the first funding period of this project, we synthesized octahedral Pt nanoparticles with controlled size and surface compositions, used different post-synthesis methods to optimize their surface structure, studied their electrochemical activity and stability, and monitored the structural evolution of the catalysts throughout the whole process by analytical electron microscopy. The aim was to correlate the atomic-scale microstructural evolution with their electrocatalytic activities and long term stabilities, ultimately aiding with strategies for producing more stable catalysts. In particular, we have exemplified that surface doping with Rhodium could substantially increase the shape stability and maintain a high activity of the octahedral catalysts. The overarching goal of our follow-up project proposal are methodological and conceptual advances in the microstructural analysis and description of multi-metallic electrocatalysts, combined with a deeper understanding of their surface chemistry and structural evolutions of surface-doped shaped PtNi nanoparticles under operating electrocatalytic conditions. We will achieve this general goal by exploring the effects of specific synthetic-methodological approaches on the chemical and structural transformations of shaped alloy electrocatalysts in increasingly realistic “in situ” and ultimately “operando” conditions. More specifically, we will focus i) on a systematic investigation of surface doping effects on structural/compositional stability, on ii) on in situ chemical and thermal post-synthesis treatments and their effect on morphology, structure and composition, iii) on in-situ studies of the interaction of reactive gases with the electrocatalyst surface and finally iv) on in-situ and operando studies of electrocatalysts in electrochemical liquid cells.