Impact of Support Physicochemical Properties on the CO Oxidation and the Oxygen Reduction Reaction Activity of Pt/SnO₂ Electrocatalysts

The interaction between Pt catalysts for the electrochemical oxygen reduction reaction (ORR) and corrosion-resistant SnO₂ supports has been studied by varying the Pt morphology and the SnO₂ physicochemical properties in a model electrode study. Different Pt morphologies ranging from isolated particles to thin films have been deposited by magnetron sputtering on oxidized and reduced SnO₂ model film electrodes as well as on glassy carbon (GC). Furthermore, three different surface probe reactions, namely the hydrogen underpotential deposition (H_upd), the CO oxidation, and the ORR have been studied to investigate the support influence on the Pt electrocatalytic properties. A marked effect of the type of the support, that is, tin oxide versus carbon, on the Pt electrochemically active surface area calculated from the H_upd charge was observed. Furthermore, a pronounced CO oxidation activity of Pt deposited on SnO₂ supports was observed compared to that of Pt supported on GC. The intrinsic ORR activities of Pt/SnO₂ and Pt/GC catalysts varied with both the Pt morphology and the SnO₂ stoichiometry. While very similar ORR activities of all catalysts were found at high Pt loadings where an extended surface Pt morphology is expected, a strong support dependence was observed for isolated Pt particles at low Pt loadings. Pt nanoparticles supported on reduced SnO₂ and on GC showed very comparable ORR activities, about five times higher than that of Pt nanoparticles on oxidized SnO₂. Postmortem X-ray photoelectron spectroscopy investigations revealed that the reduced ORR activity of the latter catalysts can be explained with a stronger oxidation of Pt nanoparticles when supported on oxidized SnO₂. This finding highlights the fundamental importance of tailoring the oxide support properties to maximize the Pt electrocatalyst performance

Combining SAXS and XAS To Study the <i>Operando</i> Degradation of Carbon-Supported Pt-Nanoparticle Fuel Cell Catalysts

In the last two decades, small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) have evolved into two well-established techniques capable of providing complementary and <i>operando</i> information about a sample’s morphology and composition, respectively. Considering that operation conditions can often lead to simultaneous and related changes in a catalyst’s speciation and shape, herein we introduce a setup that combines SAXS and XAS in a configuration that allows optimum acquisition and corresponding data quality for both techniques. To determine the reliability of this setup, the latter was used to study the <i>operando</i> degradation of two carbon-supported Pt-nanoparticle (Pt/C) catalysts customarily used in polymer electrolyte fuel cells. The model used for the fitting of the SAXS curves unveiled the fractal nature of the Pt/C-electrodes and their evolution during the <i>operando</i> tests, and both X-ray techniques were complemented with control, ex situ transmission electron microscopy, and standard electrochemical measurements. Ultimately, the results obtained with this combined setup quantitatively agree with those reported in previous studies, successfully validating this apparatus and highlighting its potential to study the <i>operando</i> changes undergone by worse-understood (electro)­catalytic systems