Directly constructing Pt-, Pd-, or Au-based high-index skins on Ag nanocubic templates from a general surface-confined anisotropic etching strategy

Abstract

Pursuing a general and feasible method to construct precious metal (PM) nanostructures bounded by high-index facets (HIFs) is highly desirable for both academic and industrial interests in promising metal materials. Herein, attempts to employ modified galvanic replacement processes between MCl_x^y− (M = Pt, Pd or Au) PM precursors and sacrificed templates of Ag nanocubic particles with deliberately introduced high [Cl⁻] (concentration of Cl⁻) were investigated to gain more acceptable HIF PM nanostructures. Typically, the Pt–Ag system was chosen as a representative system and monitored by the comprehensive characterizations of UV-vis, XRD, XPS and TEM to illuminate the evolution of the corresponding particles. It was demonstrated that the deliberately introduced Cl⁻ at a certain concentration ([Cl⁻] was not lower than 1.5 M) could play dual roles in the kinetic evolution of the particles: one was dramatically lowering the etching speed to confine the reaction to the surface layers of the Ag substrates, and the other was facilitating the anisotropic etching process along the PVP-protected Ag surface through the Nernst–Einstein diffusion influence on PtCl₄²⁻, which in turn led to the formation of concave nanocubic particles with Pt-highly-dispersed [hk0] high-index surfaces (combined by the [210], [410] and [510] atomic terraces) on the Ag templates. The efficiencies of the method were further confirmed by constructing similar Pd- or Au-highly-dispersed high-index surfaces on Ag templates, suggesting that the method is a novel and general strategy to directly construct PM-based high-index surfaces with high PM dispersion in bimetallic nanostructures, which could be referenced as a solution to obtain superior precious metal materials possessing both unique HIF surface configuration and cost-saving competitiveness for advanced applications.