Importance of defective structure of ceria additive on selectivity and stability of carbon-supported low-Pt-content-catalysts during oxygen reduction

Abstract

Benchmark carbon/Vulcan-supported Pt nanoparticles have been subjected to interfacial modification with defective ceria (CeOx, 1.5<x≤2) nanostructures to clarify the influence of the metal oxide additive on the activity, selectivity, and stability of the low-Pt-content (Pt loading, 15 µg cm−2) electrocatalysts during the oxygen reduction reaction (ORR) in acidic medium. The prepared three-component (Pt, C, CeOx) hybrid catalytic materials have been rigorously characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), while the electrocatalytic and general electrochemical properties have been diagnosed using rotating ring-disk electrode (RRDE) voltammetry, chronocoulometry, and gas diffusion electrode methods. The NAP-XPS and Raman data have revealed that, among the distinct ceria additives studied, fine nanoparticles of cerium oxide deposited in situ on Vulcan XC-72 support are characterized by the most considerably defective structure with a noticeable amount of Ce(III). The results of electrochemical and NAP-XPS experiments imply the existence of strong mutual interactions between the defective ceria, platinum, and carbon components. The substoichiometric features of the ceria additive have been correlated with the ability of the low-Pt-content hybrid catalyst to minimize the formation of the undesirable hydrogen peroxide intermediate and promote the 4-electron ORR. On the whole, the addition of CeOx/C to Vulcan-supported Pt catalyst leads to their improved durability during prolonged potential cycling under RRDE voltammetric conditions. In the presence of ceria, the desorptive oxidation of poisoning CO-type adsorbates (that may originate from corrosion of carbon carriers) is largely enhanced.