One-step fabrication of Au@Pd core-shell bimetallic nanofibers at the interface between water and redox-active ionic liquid

Abstract

Au@Pd core-shell bimetallic nanofibers (BNFs) have been successfully prepared with a one-step fabrication method, where no additional preparation step using a template is required. The preparation is realized by the spontaneous growth of Au@Pd BNFs at the interface between water (W) and a hydrophobic redox-active ionic liquid (RAIL). The RAIL plays dual roles of reducing agent to reduce metal precursors dissolved in W, AuCl₄⁻ and PdCl₄²⁻, at the RAIL|W interface, as well as the hydrophobic liquid phase constituting the RAIL-W two-phase system. The reduction reactions of AuCl₄⁻ and PdCl₄²⁻ at the RAIL|W interface proceed sequentially; AuCl₄⁻ is reduced prior to PdCl₄²⁻ to produce Au nanofibers, which act as the core for the following deposition and growth of Pd shell on the Au surface. Thus, the reductive formation of Au as the core and that of Pd as the shell can be automatically completed in one step. The mechanisms for the interfacial charge transfer reactions and the growth of Au@Pd BNFs are discussed in detail. Control experiments have clearly confirmed that the RAIL greatly promotes the reduction of PdCl₄²⁻and prevents the agglomeration of Au@Pd BNFs. The prepared Au@Pd BNFs exhibit higher electrocatalytic performance towards ethanol oxidation reaction than the commercial Pd/C catalyst, and the catalytic activity is even improved after long-time cycles. TEM images reveal a structural transformation of the Pd shell in the Au@Pd BNFs after long-time cycles, which is responsible for the increased catalytic activity.