Facile Synthesis of Pd@Pt_3<b>-</b>4LCore-Shell Octahedra with a Clean Surface and Thus Enhanced Activity toward Oxygen Reduction

The presence of a capping agent or stabilizer in the synthesis of colloidal metal nanocrystals will compromise their performance if employed as electrocatalysts. Herein we demonstrate the synthesis of Pd@Pt3–4L core–shell octahedral nanocrystals with greatly enhanced activity toward the oxygen reduction reaction by eliminating the use of any capping agent or stabilizer. This was achieved by employing Pd octahedral seeds with well-defined {1 1 1} facets and by dispersing them on a carbon black support prior to Pt deposition. Upon optimization of the reaction conditions, Pt ultrathin shells could be conformally deposited on the Pd octahedral seeds in a layer-by-layer fashion without involving self-nucleation or island growth for the Pt atoms. The as-obtained octahedral Pd@Pt3–4L/C catalyst exhibited a specific activity 50 % greater than that of a reference sample prepared in the presence of a polymer stabilizer such as poly(vinyl pyrrolidone). The polymer-free catalyst also showed 5-fold enhancement in specific activity if benchmarked against a commercial Pt/C catalyst.