title: Low-coordination sites in oxygen-reduction electrocatalysis: their roles and methods for removal.
abstract: Low-coordination sites, including edges, kinks, and defects, play an important role in oxygen-reduction electrocatalysis. Their role was studied experimentally and theoretically for various Pt surfaces. However, the roughness effect on similar-sized nanoparticles that could elucidate the role of low-coordination sites has attracted much less attention, with no studies on Pd nanoparticles. Here, using Br- adsorption/desorption, we introduce an effective approach to reduce surface roughness, yielding Pd nanoparticles with smoother surfaces and an increased number of (111)-oriented facets. The resulting nanoparticles have a slightly contracted structure and narrow size distribution. Pt monolayer catalysts that contain such nanoparticles as the cores showed a 1.5-fold enhancement in specific and Pt mass activities for the oxygen reduction reaction compared with untreated ones. Furthermore, a dramatic increase in durability was observed with bromide-treated Pd(3)Co cores. These results demonstrate a simple approach to preparing nanoparticles with smooth surfaces and confirm the adverse effect of low-coordination sites on the kinetics of the oxygen-reduction reaction.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Cai
authors.forename: Chao
authors.initials: C
authors.lastname: Ma
authors.forename: Yimei
authors.initials: Y
authors.lastname: Zhu
authors.forename: Jia X
authors.initials: JX
authors.lastname: Wang
authors.forename: Radoslav R
authors.initials: RR
authors.lastname: Adzic