Icosahedral Pt-Ni Nanocrystalline Electrocatalyst: Growth Mechanism and Oxygen Reduction Activity

Abstract

Engineering the structure of Pt alloy offers an effective way to the design of high performance electrocatalysts. Herein, we synthesize a sandwich-structured, icosahedral Pt_2.1 Ni catalyst through a hot injection method. Its growth involves three steps: 1) burst nucleation of Pt atoms to form a Pt-enriched core, 2) heterogeneous nucleation of Ni atoms onto the Pt core to form a Ni-enriched interlayer, and 3) kinetic controlled growth of a Pt-enriched shell. The Pt-enriched core protects the nanostructure from collapse and mitigates the strain change caused by lattice mismatch, and thus enhances the stability of the structure. The Ni-enriched interlayer induces the electronic modification of the outermost Pt shell, and in turn tunes the activity. The Pt-enriched shell provides more active sites through the exposure of (1 1 1) facets and retards the dissolution of Ni atoms. As a result, this sandwich-structure enables impressive electrocatalytic activity (0.91 mA cm^-2 and 0.32 AmgPt-1 @ 0.9 V) and duability.

Keywords: growth mechanism; oxygen reduction reaction; platinum alloy; proton exchange membrane fuel cell; sandwich structure.