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引起了人们的极大兴趣。在不影响燃料电池的活性和长期稳定性的情况下，减少稀有和昂贵的铂作为燃料电池中的催化剂材料的数量尤为重要。八面体形状的铂镍纳米粒子作为PEM燃料电池的催化剂表现出了优异的性能。然而，通常情况下，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其原子级结构密切相关，而原子级结构是由纳米颗粒的合成和合成后处理提供的。因此，了解纳米催化剂的生长和降解的原子机理，对于调整纳米催化剂的性能具有重要意义。在本项目的第一个资助期，我们合成了尺寸和表面组成可控的八面体铂纳米粒子，采用不同的合成后方法对其表面结构进行了优化，研究了其电化学活性和稳定性，并通过分析电子显微镜全程监测了催化剂的结构演变。其目的是将原子尺度的微结构演变与它们的电催化活性和长期稳定性联系起来，最终有助于生产更稳定的催化剂。特别是，我们已经举例说明了表面掺杂Rh可以显著提高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首要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学和概念性的进展，并更深入地了解它们的表面化学和表面掺杂成形PtNi纳米粒子在运行电催化条件下的结构演变。我们将通过探索特定的合成方法学方法对成型合金电催化剂在越来越现实的“原位”和最终“操作式”条件下的化学和结构转化的影响来实现这一总体目标。更具体地说，我们将集中于i)表面掺杂对结构/组成稳定性的影响的系统研究，ii)原位化学和热后合成处理及其对形态、结构和组成的影响，iii)反应气体与电催化剂表面相互作用的原位研究，以及iv)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.