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Nanoframes with 3D Electrocatalytic Surfaces

Multimetallic nanoframes with 3D surfaces imageMultimetallic nanoframes with 3D surfaces: Structural evolution of nanoparticles from: (A) polyhedra,  (B) intermediates,  (C) nanoframes and (D) nanoframes with multilayered Pt-Skin structure; and (E) superior electrochemical activities for ORR and HER compared to state-of-the-art Pt/C catalysts

“Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces,” C. Chen et al., Science 343, 1339-1334, 2014 DOI: 10.1126/science.1249061

Scientific Achievement
Synthesized nanoframes that allow 3D molecular accessibility to platinum-rich surfaces, achieving electrocatalyst with high surface-to-volume ratio and control of surface chemistry.

Significance and Impact
Superior electrocatalytic properties of crystalline alloyed nanoscale materials optimize precious metal use and reaction activity.

Summary
Control of atomic level structure can precisely tune catalytic properties of materials, enabling enhancement in both activity and durability. Members of the Chemical and Mechanical Properties of Surfaces Program program has synthesized a highly active and durable class of electrocatalysts by exploiting the structural evolution of Pt-nickel alloy nanocrystals. The starting material, crystalline PtNi3 polyhedra, is transformed in solution by interior erosion into Pt3Ni nanoframes with surfaces that have three-dimensional molecular accessibility.  The edges of these polyhedra, which are rich in Pt, are maintained in the final nanoframes; all the Pt atoms are accessible.  Both the interior and exterior catalytic surfaces of this open framework structure are composed of the Pt-Skin structure that exhibits enhanced oxygen reduction reaction (ORR) activity, one of the desired outcomes. The Pt3Ni nanoframe catalysts achieved over 36- and 22-fold enhancement in mass and specific activities, respectively, for this reaction versus ORR in comparison to state-of-the-art Pt/C catalysts.

The open structure of the Pt3Ni nanoframes addresses several major design criteria for advanced nanoscale electrocatalysts including high surface-to-volume ratio, 3D surface molecular accessibility, and optimal precious metal utilization.  The approach presented for the structural evolution of a bimetallic nanostructure from solid polyhedra to hollow crystalline nanoframes with controlled size, structure and composition is readily applicable to other alloyed electrocatalysts.