Electrodeposition and Characterization of Ultra-Thin Films As Model Systems for Electrocatalysis

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. This catalytic 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, enabling their use as model surfaces in synchrotron light experiments (performed at the BM-08 line of 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, with this novel set-up we just sampled the topmost catalytic layer, thus greatly enhancing the capability to study small modifications of the surface.