Nanoscale Pt Alloy electrocatalysts with well-defined shapes: Synthesis, Electrochemical Analysis, and ex-situ/in-situ TEM Studies

• Applicants: Dr. Marc Heggen; Professor Dr. Peter Strasser
• Subject Area: Synthesis and Properties of Functional Materials ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2014 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257727131

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.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partner: Professor Dr. David Muller