Pt/IrO 2 bifunctional catalysts synthesized with varying Pt:Ir ratios and characterized using several techniques, including energy dispersive X-ray spectroscopy, transmission electrons microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, were investigated for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in acid media. Three stability testing protocols are used to evaluate the catalysts stabilities, comprising electrode cycling in the ORR, OER, and ORR−OER potential ranges. Electrochemical results provide evidence that a Pt/IrO 2 1:9 material exhibits better balance between the OER and ORR mass activities and that cycling in the ORR-OER potential window is the most aggressive aging protocol for the Pt/IrO 2 materials. Identical location transmission electron microscopy is used to investigate the aging processes taking part in the Pt/IrO 2 catalysts. In addition to dissolution processes, particle coalescence, growth, and detachment are confirmed as responsible for the Pt/IrO 2 instability.
The increasing global needs for clean and renewable energy have fostered the design of new and highly efficient materials for fuel cells applications. In this work, Pd-M (M = Pd, Cu, Pt) and Pt nanoparticles were prepared by a green synthesis method. The carbon-supported nanoparticles were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. A comprehensive electronic and structural characterization of these materials was achieved using X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Their electrochemical properties were investigated by cyclic voltammetry, while their activities for the ORR were characterized using steady-state polarization experiments. The results revealed that the bimetallic nanoparticles consist of highly crystalline nanoalloys with size around 5 nm, in which the charge transfer involving Pd and M atoms affects the activity of the electrocatalysts. Additionally, the samples with higher ORR activity are those whose d-band center is closer to the Fermi level.
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