XPS and STEM study of the interface formation between ultra-thin Ru and Ir OER catalyst layers and Perylene Red support whiskers

The interface formation between nano-structured Perylene Red (PR) whiskers and the oxygen evolution reaction (OER) catalysts ruthenium and iridium was studied systematically by XPS and STEM. The OER catalyst overlayers with thicknesses ranging from ≈0.1 to ≈50 nm were vapor deposited onto PR ex situ. STEM images demonstrated that, with increasing thickness, Ru and Ir transform from amorphous clusters to crystalline nanoparticles, which agglomerate with increased over-layer thickness. XPS data showed 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 was in the reacted state while a small portion of the deposited Ir remained 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 bonds. Curve fitting analysis and the derived stoichiometry indicated the formation of metallo-organic bonds. The co-existence of oxide bonds was also apparent.