The effect of interfacial pH on the surface atomic elemental distribution and on the catalytic reactivity of shape-selected bimetallic nanoparticles towards oxygen reduction

Abstract

The effect of interfacial pH during the surface cleaning of shape-selected PtNi nanoparticles was investigated. High-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) and energy-dispersive X-ray (EDX) elemental mapping techniques were used to analyze the morphology and composition of the particles at the nanoscale. The particles show similar atomic compositions for both treated samples but different elemental distribution on the surface of the nanooctahedra. X-ray photoelectron spectroscopy (XPS) analysis confirmed different surface compositions and the presence of different oxidation states species at the outer part of the nanoparticles. In addition, we compare characteristic voltammetric profiles of these nanocatalysts when immersed in three different aqueous supporting electrolytes (H2SO4, HClO4 and NaOH). The behavior of the bimetallic nanoparticles towards adsorbed CO oxidation has been analyzed and compared with that observed after surface disordering of the same catalysts. The electrocatalytic activity of these nanoparticles has been also tested for the electroreduction of oxygen showing high specific and mass activity and better catalytic performance than pure Pt shaped nanoparticles. The different treatments applied to the surface of the nanocatalysts have led to remarkably different catalytic responses, pointing out the outstanding importance of the control of the surface of the alloyed shape-selected nanoparticles after their synthesis and before their use as electrocatalysts.