FEXRAV (Fixed Energy X-ray Absorption Voltammetry) is an experimental method that couples cyclic voltammetry (CV), with X-ray Absorption Spectroscopy (XAS). The approach supply the conventional information that can be derived by the analysis of the cyclic voltammetry with the information on the chemical state of the elements provided by the pre-edge and edge analysis of the XAS spectra (XANES). In addition, short range structural data can be obtained by the analysis of the post edge region (EXAFS) at fixed potential. Accordingly, FEXRAV is a powerful tool to understand the chemical and structural modifications occurring at the electrode surface under the application of an external potential. This approach is extraordinary powerful we propose it as a new tool to understand the formation of oxide thin films on metals in electrochemical environment.
This contribution reviews the fundamental principles, the electrochemical cell design, and the synchrotron beamline set-up that enable the collection of FEXRAV data. As a case study, we report the investigation of palladium oxidation in alkaline media, a subject of extreme importance for fuel cell technology and generally for electrochemical energy conversion and storage. With our investigation we have discovered that palladium oxidation occurs at potential larger than 0.65 V (RHE), that such oxidation occurs even in presence of alcohols and that the passivation layer blocks out the capability of palladium to oxidize alcohols. Remarkably, these conditions happen in real systems and are responsible of the loss of efficiency of direct alcohol fuel cells. We have also found that the presence of promoting metal oxide in contact with Pd accelerate the oxidation and, ultimately, is detrimental for the stability of the devices.
|Category||Short file description||File description||File Size|