In-Situ Laser Diagnostics of Metal Nanoparticles during Their Flame Synthesis in the Reactive Spray Deposition Technology

EVANGELOS K. STEFANIDIS, Thomas A Ebaugh, Stoyan Bliznakov, Leonard Bonville, Radenka Maric, Francesco Carbone, University of Connecticut

     Abstract Number: 453
     Working Group: Nanoparticles and Materials Synthesis

Abstract
The development of proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) requires enhanced techniques for manufacturing highly active and durable catalysts and Membrane Electrode Assemblies (MEAs). Reactive Spray Deposition Technology (RSDT) is an atmospheric pressure flame-assisted MEA fabrication methodology that combines catalyst synthesis and MEA manufacturing in one step. In RSDT, the properties of metal nanoparticles with high catalytic activity are tailored via control of the flame boundary conditions, and the synthesized catalyst nanoparticles are deposited directly on the proton conductive membrane. Currently, the RSDT process parametrization is based on the post-deposition ex-situ analysis of the fabricated catalysts. Laser diagnostics can expedite the parameters optimization significantly by measuring some characteristics of the synthesized nanoparticles in-situ in the flame during their synthesis.

In this work, we demonstrate the capabilities of the laser diagnostic system for the in-situ characterization of nanoparticles synthesized by the RSDT using three different flames. Specifically, two flames are fueled by a solution mixture of xylene, acetone, propane, and platinum acetylacetonate but differ in the reactant flow rates, whereas the third flame relies on a solution mixture of xylene, ethanol, diethylene glycol monoethyl ether (DGME), propane, and iridium acetylacetonate. Laser-Induced Incandescence (LII) is used to characterize the dilution and the change in optical properties of the synthesized nanoparticles, whereas Laser Light Scattering (LLS) is used to measure their size as they travel and age downstream of the flame. The in-situ results from both LII and LLS techniques are compared with ex-situ results obtained by analyzing thermophoretic samples of the nanoparticles acquired by High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM). We found that the laser measurements of LII and LLS agree with the HAADF-STEM results. Finally, we measured the Raman scattering spectra of the iridium nanoparticles synthesized in the third flame to identify possible chemical functional groups on the nanoparticles’ surface.