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

• Applicant: Professor Dr. Peter Strasser
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256186919

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.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Person: Professor Dr. Vijay Ramani