Tensile-Strained Platinum-Cobalt Alloy Surface on Palladium Octahedra as a Highly Durable Oxygen Reduction Catalyst.

Designing shape-controlled Pt-based core-shell nanocrystals is a prospective strategy to maximize the utilization of Pt while maintaining high activity for oxygen reduction reaction (ORR). However, the core-shell structures with ultrathin Pt shell exhibit limited electrochemical durability. Therefore, a thicker shell is proposed to successfully improve the durability of the core-shell structures by preventing the core from dissolution. Nevertheless, the deposition of Pt tends to switch to the Stranski-Krastanov (S-K) growth mode with the increase of the number of layer, resulting in the absence of a conformal morphology. Herein, we realize the deposition of three-to-five-layer epitaxial Pt-Co layers on Pd octahedral seeds by introducing tensile strain in the epitaxial layer to impede the S-K growth. The as-obtained Pd@Pt-Co octahedra with four layers exhibit enhanced mass activity (0.69 A/mg Pt ) and specific activity (1.00 mA/cm 2 ) for ORR, which are 4.93 and 5 times that of the commercial Pt/C, respectively. Furthermore, it shows only 17% decay for specific activity after a 30,000-cycle durability test. This work is expected to enlighten the design and synthesis of related core-shell nanocrystals with facetted multicomponent shells, offering a promising strategy for designing cost-effective and efficient catalysts.