Synthesis of facetted Pt nanoparticles on SnO2 as an oxygen reduction catalyst

Abstract

Fuel cells are an important technology to match the volatile energy production with the energy demand in a sustainable energy system. One crucial task is to raise the Pt mass specific activity of Pt oxygen reduction catalysts in fuel cells and to increase their stability. Therefore, different approaches are investigated like the facetting of Pt nanoparticles and the use of supporting particles like SnO₂, which stabilize Pt. For the first time, the growth of facetted Pt nanoparticles on SnO₂ nanoparticles is reported which combines both approaches. The synthesis is based on a polyol process and employs Ag ions to influence the shape evolution of the Pt nanoparticles. The samples were studied by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and cyclic voltammetry (CV). Since SnO₂ is etched during the original synthesis, KOH is added to compensate the protons released. The fraction of the facetted Pt nanoparticles is lowered in the presence of SnO₂ likely due to adsorption of Ag on the SnO₂ surface and, thus, a decrease of the Ag concentration in the bulk solution. Consequently, the Ag concentration was increased leading to the generation of a fair amount of facetted Pt nanoparticles. To avoid the occupation of Ag redeposited on the Pt catalyst's surface and, thus, lowering of its catalytic activity, a cleaning procedure consisting of potentiostatic oxidation of Ag and replacement of the electrolyte was applied.