Research Group - Prof. Mehtap Özaslan

Dealloying of alloy nanoparticles (NPs) has emerged as promising route to prepare highly active and durable catalysts for heterogeneous and electrochemical reactions, for example the methanol oxidation reaction (MOR).  Porous NPs show high surface area-to-volume ratios and enable to tune its pore confinement and surface curvature probably leading to an improvement of the reaction kinetics.

The particle diameter as well as the chemical composition of the pristine alloy NPs play a very critical role in the design of nanoporous noble metal-rich NPs with advanced functionality. In particular, small bimetallic NPs form core-shell structures during the dealloying process, while bigger NPs generate a sponge-like porous structure. The final structure of the dealloyed NPs can also be tuned by the dealloying conditions (electrolyte, potential, temperature, etc.). Therefore, the questions arise what critical particle size and chemical composition lead to the formation of nanoporous NPs and can the dealloying parameters control the lattice strain and chemical distribution inside these porous particles.

Within this sub-project, all these fundamental questions will be investigated. Our goal is to design porous Au-rich NPs with controlled particle size, pore size and content of less noble metal. These NPs will be prepared from Ag-Au and Cu-Au alloys nanoparticles by applying different (electro)chemical dealloying conditions. We will clarify the formation mechanisms of the porous Au-rich NPs as the function of the particle size and chemical composition of the pristine alloy NPs. The strain and the chemical distribution of Au and Ag/Cu atoms inside the dealloyed Au-based NPs will be analyzed by synchrotron-based X-ray absorption spectroscopy (XAS) and high-angle annular dark-field scanning transmission electron spectroscopy (HAADF-STEM). The HAADF-STEM analysis will be performed in collaboration with sub-project SP6 in the group of A. Rosenauer.

In order to gain insight on the catalytic activity of Au-rich NPs of different sizes and shapes (core-shell, hollow and porous nanoparticles) they will be tested for the electrochemical methanol oxidation reaction (MOR). The MOR results will be compared not only between the different NPs but also with the results obtained for porous bulk electrodes in the group of Prof. Wittstock in SP4.