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

这项研究的目的是在氧氧化还原电极高度腐蚀性的电化学条件下，为控制负载型铂纳米粒子系综的形态(In)稳定性的化学和结构参数提供基本的见解。负载型纳米粒子的形态稳定性反映在其抗颗粒团聚或成熟引起的脱落、长大或粗化的能力上。具体地说，在铂稳定性的情况下，该项目将调查i)初始颗粒尺寸分布(PSD)，ii)电催化剂载体材料的化学性质，iii)平均尺寸和iv)施加的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，将特别强调铂纳米颗粒在新型非碳、氧化性高比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，且铂颗粒与载体之间的化学作用较强，则可以提高铂纳米颗粒的稳定性。这些新的见解将加深对铂颗粒降解基本机理的基本理解，并将开创在燃料电池中使用电化学稳定且成本效益高的非碳电催化剂载体的先河。因此，这两项公开将导致PEFC的改进的铂电极的设计，这对于燃料电池技术的商业化非常重要。本项目采用的实验方法包括由无机氧化物(如二氧化钛、二氧化铈、氧化锡等)制成的非碳载体的溶剂热合成。使用电子显微镜和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)，将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提供了同时检测铂/碳的电子参数和几何参数的变化的能力；光谱的近边缘部分(XANES)提供了对铂5d带空位/原子的直接测量，而光谱的后边缘部分(EXAFS)监测了铂的最近邻相互作用(键距和配位数)的变化。循环伏安图以及BET测量、能量色散X射线能谱(EDX)、透射电子显微镜(TEM)测量将提供有关新氧化物载体的铂负载量和颗粒大小以及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.