In this paper, we provide an overview of several recent development activities towards improving the activity of nanoporous PtxNi1-x thin film electrocatalysts on the 3M Nanostructured Thin Film (NSTF) support. Significant improvements in electrocatalyst specific area and mass activity have been achieved through optimization of electrocatalyst fabrication parameters (deposition, annealing, and dealloying), which influence electrocatalyst composition and structure. Membrane electrode assemblies (MEAs) which incorporate improved NSTF PtxNi1-x cathode catalysts have demonstrated performances which approach or exceed several U.S. Department of Energy 2020 performance and PGM-content targets.
In this paper, we review our development activities of ultrathin film (UTF) PtNi and PtNiIr oxygen reduction reaction electrocatalysts on 3M Nanostructured Thin Film supports. Significant improvements in electrocatalyst mass and specific activities have been achieved through optimization of electrocatalyst bulk and surface compositions and structures. The compositional and structural factors influencing catalyst activity were investigated by high resolution electron microscopy and xray adsorption spectroscopy, and modeled by density functional theory. Membrane electrode assemblies which incorporate UTF PtNi and PtNiIr cathode catalysts have demonstrated performance and durability which approach or exceed several U.S. Department of Energy 2020 performance, durability, and platinum group metal content targets.
The interface formation between perylene red (PR) and ruthenium or iridium OER catalysts has been studied systematically by XPS and STEM. The OER catalyst over-layers with thicknesses ranging from ~0.1 to ~50 nm were vapor deposited onto PR ex-situ. As seen by STEM, Ru and Ir form into nanoparticles, which agglomerate with increased loading. XPS data show a strong interaction between Ru and PR. Ir also interacts with PR although not to the extent seen for Ru. At low coverages, the entire Ru deposit is in the reacted state while a small portion of the deposited Ir remains metallic. Ru and Ir bonding occur at the PR carbonyl sites as evidenced by the attenuation of carbonyl photoemission and the emergence of new peak assigned to C-O single bond. The curve fitting analysis and the derived stoichiometry indicates the formation of metallo-organic bonds. The co-existence of oxide bonds is also apparent.
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