On the morphological stability of supported Pt nanoparticle ensembles in electrochemical environments

提出的研究旨在为在氧氧化还原电极的高腐蚀性电化学条件下控制负载Pt纳米颗粒系综形态稳定性的化学和结构参数提供基本见解。负载纳米颗粒的形态稳定性反映在其抗脱落、抗生长或抗颗粒团聚或成熟导致的粗化。具体而言，在铂稳定性方面，该项目将研究i)初始粒径分布（PSD）， ii)电催化剂支撑材料的化学性质，iii)平均粒径和iv)应用电化学电位循环方案对电催化剂稳定性的作用。在电催化剂载体方面，将特别强调Pt纳米颗粒在新型非碳氧化高表面积载体上的结构行为。该项目首先假设，如果初始PSD较窄，并且Pt颗粒与载体之间的化学相互作用较强，则可以提高Pt纳米颗粒的稳定性。新的见解将导致对基本Pt颗粒降解机制的更深入的基本理解，并将开创在燃料电池中使用电化学稳定且成本有效的非碳质电催化剂载体。因此，这两项公开将导致设计用于pefc的改进Pt电极，这对燃料电池技术的商业化具有重要意义。本项目采用的实验方法包括溶剂热合成由无机氧化物（如二氧化钛、铈、氧化锡等）制成的非碳载体。利用电子显微镜和x射线散射技术，如电化学广角x射线散射和小角x射线散射（SAXS），在电化学电位循环方案之前、期间和之后监测电催化活性和形态稳定性。电子结构和几何结构对电催化活性的影响将通过原位x射线吸收光谱（XAS）研究来检验。XAS提供了同时检测Pt/C电子和几何参数变化的能力；光谱的近边缘部分（XANES）提供了Pt 5d带空位/原子的直接测量，而光谱的后边缘部分（EXAFS）监测了Pt的最近邻相互作用（键距和配位数）的变化。循环伏安图以及BET测量、能量色散x射线光谱（EDX）、透射电子显微镜（TEM）测量将提供有关新型氧化载体的Pt负载和粒径及其ECA损失的详细信息。

The proposed research aims to provide fundamental insight in the chemical and structural parameters that control the morphological (in)stability of supported Pt nanoparticle ensembles under the highly corrosive electrochemical conditions of oxygen redox electrodes. Morphological stability of supported nanoparticles is reflected on the resistance to detachment, growth or coarsening due to particle agglomeration or ripening. Specifically, in the case of Pt stability, the project will investigate the role of i) the initial particle size distribution (PSD), ii) the chemical nature of the electrocatalyst support material, iii) the mean size and iv) the applied electrochemical potential cycling protocols on electrocatalyst stability. On the electrocatalyst support front, special emphasis will be placed on the structural behavior of Pt nanoparticles when supported on novel non-carbonous, oxidic high surface area supports. The project starts with the hypothesis that the stability of Pt nanoparticles can be improved if the initial PSD is narrow and the chemical interaction between Pt particles and support is strong. The new insights will lead to a deeper basic understanding of the fundamental Pt particle degradation mechanisms and will pioneer the use of electrochemically stable and cost effective non-carbonaceous electrocatalyst supports in fuel cells. Thus, both disclosures will lead to the design of improved Pt electrodes for PEFCs which is of great importance for the commercialization of the fuel cell technology.Experimental methods employed in this project comprise solvothermal synthesis of non-carbon supports made of inorganic oxides (such as titania, ceria, tin oxide and others). Electrocatalytic activity and morphological stability will be monitored before, during, and after electrochemical potential cycling protocols using electron microscopy and X-ray scattering techniques such as electrochemical wide angel X-ray scattering and small angle x-ray scattering (SAXS). The effect of electronic and geometric structure on electrocatalytic activity will be examined by in-situ X-ray absorption spectroscopy (XAS) studies. XAS offers the ability to detect simultaneously changes in the electronic and geometric parameters of Pt/C; the near-edge part of the spectra (XANES) provides a direct measure of Pt 5d-band vacancies/atom while the post-edge part of the spectra (EXAFS) monitors the changes in the nearest neighbor interactions of Pt (bond distance and coordination number). Cyclic voltammograms as well as BET measurements, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) measurements will provide detailed information regarding Pt loading and particle size of the new oxidic supports as well as their ECA losses.