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于未来的能量转换和存储应用非常重要。质子交换膜（PEM）燃料电池作为用于移动的和固定装置的清洁电源正吸引特别的兴趣。特别重要的是减少燃料电池中作为催化剂材料的稀有且昂贵的Pt的量，而不损害活性和长期稳定性。八面体形状的Pt-Ni纳米颗粒作为PEM燃料电池的催化剂已经显示出优异的性能。然而，通常，这种成型催化剂缺乏长期稳定性，例如由于形状损失。它们的电化学活性和稳定性与它们的原子级结构密切相关，所述原子级结构由纳米颗粒的合成和合成后处理提供。因此，理解生长和降解的原子机制以调节催化剂纳米颗粒的性能是非常重要的。在该项目的第一个资助期内，我们合成了具有可控尺寸和表面组成的八面体Pt纳米颗粒，使用不同的合成后方法优化其表面结构，研究其电化学活性和稳定性，并通过分析电子显微镜监测整个过程中催化剂的结构演变。其目的是将原子尺度的微观结构演变与其电催化活性和长期稳定性相关联，最终有助于生产更稳定的催化剂的策略。特别地，我们已经举例说明了用铑进行表面掺杂可以显著增加八面体催化剂的形状稳定性并保持高活性。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，并更深入地了解其表面化学和表面掺杂的形状PtNi纳米颗粒在操作电催化条件下的结构演变。我们将实现这一总体目标，探索具体的合成方法的影响，在日益现实的“原位”和最终的“操作”条件下的化学和结构转变的形状合金电催化剂。更具体地说，我们将集中i）对结构/组成稳定性的表面掺杂效应的系统调查，ii）在原位化学和热合成后处理及其对形态，结构和组成的影响，iii）在原位研究的反应性气体与电催化剂表面的相互作用，最后iv）在电化学液体电池中电催化剂的原位和operando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.