WEB A model system to investigate palladium ultra-thin films electrooxidation by X-ray Absorption SpectroscopyWednesday (01.01.2020) 00:30 - 00:45 Part of:
Platinum is nowadays considered the best catalyst for many anodic and cathodic reactions in fuel cells. However, its low abundance poses a limit for its usage in such devices. In recent years, much effort has been done to substitute this metal whit more abundant ones, in particular concerning the alcohol electrooxidation process in direct alkaline alcohol fuel cells (DAFC).
In this respect, palladium (which shares with platinum a similar catalytic activity towards alcohol electrooxidation) may represent a viable substitute for the anodic compartment in DAFC, but its main limit resides in the deactivation process (oxidation of the metal) that occurs during the cell duty cycle.
Aiming to study this phenomenon, different catalytically active bimetallic Au-Pd electrodes were prepared by combined Under-Potential Deposition (UPD) of copper and Surface Limited Redox Replacement (SLRR) with Pd, exploiting homemade Au (111) polycrystalline surfaces. The obtained catalytical ultra-thin layers (with different Pd coverages above Au) proved to be robust and reproducible, both morphologically and electrochemically. Moreover, this method enabled the preparation of large, flat and homogeneous surfaces, permitting their use as model surfaces during synchrotron light experiments (performed at the ESRF in Grenoble), where a blend between the Grazing Incidence X-ray Absorption Spectroscopy (GIXAS) and the Fixed Energy X-Ray Absorption Spectroscopy (FEXRAV) was exploited. This novel experimental set-up, a grazing Incidence FEXRAV technique (GI-FEXRAV), allowed to follow in operando changes in the speciation of the Pd during voltammetric scans, and thus to disclose its deactivation/dissolution in systems with a very low catalytical load. Finally, the novel set-up permitted the sampling of the topmost catalytical layer only, thus greatly enhancing the capability to study small modifications of the surface.