Abstract
The oxidation of palladium nanoparticles causes the performance degradation of alkaline direct ethanol fuel cells. Quantifying this oxidation is a task of tremendous importance to design mitigation strategies that extend the service life of catalysts and devices. Here, we show that the Fixed Energy X-ray Absorption Voltammetry (FEXRAV) can provide this information with an in-situ approach. To do so, we have developed a quantification method that assumes the linear response at fixed energy. With this method, we have investigated the oxidation of carbon black-supported palladium electrocatalysts during cyclic voltammetry in the same solution employed as a fuel in the direct ethanol fuel cells. We have shown that up to 38% of the palladium is oxidised at 1.2 V vs RHE and that such oxidation also happens at lower potentials that the catalyst can experience in real direct ethanol fuel cells. The result of this study is a proof of concept of quantitative FEXRAV.
Highlights
Understanding electrocatalysts at work is a task of tremendous importance to design efficient fuel cells and electrolysers
We have successfully demonstrated the application of Fixed Energy X-ray Absorption Voltammetry (FEXRAV) to the quantification of the speciation of palladium in-situ, for a given sample with a defined particle distribution
We have built up a new cell design that allows the acquisition of X-ray Absorption Spectroscopy (XAS) data in Fluorescence mode and avoids the use of flow systems, overcoming two major limitations: (i) Flow systems are usually difficult to fit in the measurement XAS chamber and (ii) they cannot simulate the conditions that are commonly encountered in passive fuel cells
Summary
Understanding electrocatalysts at work is a task of tremendous importance to design efficient fuel cells and electrolysers. This can be done by methods that investigate materials in their working environment under the application of an electrical potential difference. Since the inception of high brilliance synchrotrons, in-situ XAS has unravelled surface and interphase phenomena in heterogeneous catalysis, electrocatalysis and more generally in materials science [6]. In these studies, chemical reactions and physical parameters such as temperature, pressure and, in the case of electrochemistry, potential, modify the surface composition and structure. Batteries and electrolyser efficiency and functionality largely depend on the surface of the electrocatalytic materials that can deactivate by oxidation or the adsorption of poisoning chemical species
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