Voltammetric Surface Dealloying of Pt bimetallic nanoparticles: A novel synthetic method towards more efficient ORR electrocatalysts

摘要

We report on a novel strategy to modify surface electrocatalytic reactivity of Pt bimetallic nanoparticles for the oxygen reduction reaction (ORR). We voltammetrically dealloy Cu rich Pt-Cu precursor until we obtain a Cu free catalyst surface. This dealloyed Pt surface exhibited up to fivefold improved ORR activities compared to pure Pt nanoparticle catalysts (～0.53 A/mg{sub}(Pt) and ～650μA/(cm{sup}2){sub}(Pt)). Surface area effects could be ruled out as the origin of the activity improvements. We investigate the early stages of the dealloying process for a Pt{sub}25Cu{sub}75, Pt{sub}50Cu{sub}50, and a Pt{sub}75Cu{sub}25 precursor and use a simple qualitative two layer alloy model in order to explain the resulting metal dealloying polarization curves. The model predicts that the critical corrosion (dealloying) potentials of Pt-Cu surfaces of distinct composition varies with Cu monolayers on pure Pt subsurface layers exhibiting the highest corrosion overpotentials. The model is consistent with our and previous experimental observations. The role of geometric and electronic mechanisms to explain the enhanced catalytic reactivity are discussed.