Droplet-based synthesis of metal nanoparticles at liquid/liquid interface for a biphasic catalytic synthesis of hydrogen peroxide

• Applicant: Shokoufeh Rastgar, Ph.D.
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457478500

This project deals with heterogeneous oxygen reduction reaction (ORR) at the interface between two immiscible electrolyte solutions which is optimally directed to formation of H2O2 by metallic nanoparticles (NPs) (electro)synthesized at such an interface. Metallization of the liquid-liquid (L/L) interface for instance with AuNPs effectively allows the soft interface to mimic neutral O2 reduction at a conventional solid gold electrode, with an organic-soluble electron donor species acting as the electron source and the potential at the soft “electrode” surface being adjustable by manipulating the Galvani potential difference ∆aq/o between the electrolyte solutions. The partition of ions between two phases can adjust ∆aq/o. Thus, characterization of NPs at interface is possible without the need for an external voltage source. These features make the system potentially more compatible and technically easier for further integration to characterization approaches, especially for study at miniaturized scales for instance, in a droplet reactor.First of all, the interfacial synthesis of a metal NP can be miniaturized in a droplet reactor and be then mass-produced in an array structure of micro-droplets. The same reactor can also be used to conduct the catalytic process. Those droplets will be localized in a combinatorial array at L/L interfaces for high-throughput characterization of both, structure and catalytic function of metal NPs. In such an arrangement, each droplet is a synthesis reactor of metallic NPs (at biphasic fluids) systematically varied with respect to the size, structure and composition. To construct such an array, a novel droplet-based inkjet printing will be applied in this project.Second, scanning electrochemical microscope (SECM) can be used as a characterization tool for catalytic reactions at L/L interfaces. Despite the unique features of L/L interface, the area has not been fairly progressed. This is due to a lack of tool for disentangling the complex transfer processes of electrons, ions and the neutral products. To address those issues, SECM configurations will be used in this project for a product detection (for example H2O2) during catalytic proton-coupled electron transfer (for example ORR) for following and optimizing the selectivity of the L/L system.Third, a novel electrochemical flow cell will be designed in this project utilizing L/L interfaces. This biphasic platform for catalytic chemical synthesis of H2O2 is very unique as it favors the collection of H2O2 by immediate extraction to the water phase and, thus overcomes the typical problems of such a synthesis for example, catalyst recovery, product separation and further side reactions. The designed cell will allow enhancing the efficiency of H2O2 collection and simultaneously generation of electricity. It then shapes one of the visions of this research for exergonic catalytic H2O2 synthesis.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Gunther Wittstock