Development and STM Study of Hydrogen based Deposition of Pt on Pd Thin Films
Authors: Vasiljevic Natasa , Rawlings Ben Cyril 
Published: February 2020

The key technological challenge for fuel-cells commercialization is design of nanomaterials with low-content of Pt and Pt-group noble-metals exhibiting high activity, improved selectivity and stability. New Pt-bi and tri-metallic catalysts of different shape, composition as well as geometrical configurations have been actively explored in recent years.1 Among different methods for design of Pt films, the surface limited redox replacement (SLRR) has an important place.2 This method is unique because it enables epitaxial deposition of: Pt films, monolayers and clusters, onto other noble metal surfaces with the atomic scale control. This has been achieved by utilization of underpotentially deposited (UPD) metal layer as sacrificial, in the galvanic replacement by more noble Pt.
Several research groups demonstrated successful SLRR deposition of epitaxial Pt films using Cu UPD and Pb UPD for the design of nanopraticles as well as 2D-model surfaces.3-6 Our recent work demonstrated that using the SLRR protocol, a H-UPD layer can be exploited for homoepitaxial grow of Pt. 7

We extend further the concept of H mediated growth utilizing SLRR approach, onto Pd-thin film system. Pt thin films on Au are well studied and well known for their unique H-sorption behavior, and catalytic properties.8 Moreover, recent studies on the Pt-on-Pd9 and Pt-Pd-Au10 showed that this system is of interest for its electrocatalysis as well as H- storage potential.11

Here in this talk we will present the electrochemical and the in-situ STM study of Pt electrodeposition in the SLRR configuration. Our substrates were epitaxial Pd films (2-10 ML) electrodeposited on Au(111) films evaporated on mica or glass.8 High quality of the deposited epitaxial Pd films was confirmed electrochemically and by the in-situ STM. Surface morphology evolution of Pt films was studied in solution and conducted in the environmentally isolated STM system using custom designed set up for the solutions exchange.
Furthermore, the Electrochemical Quartz Crystal Microbalance study of the growth kinetics showed that Pt structure and thickness can be controlled by the amount of absorbed hydrogen, solution pH, and Pt concentration. Electrochemical behavior of Pt films on 2ML and 10 ML Pd-Au show distinctly different H-sorption characteristics. Films on 2ML Pd/Au have characteristics of typical Pt surface, while films on the Pt-10ML Pd/Au showed uninhibited H absorption with more reversible behavior than on corresponding 10ML Pd/Au substrate.

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