Structural Transformation of Pt–Ni Nanowires as Oxygen Reduction Electrocatalysts to Branched Nanostructures during Potential Cycles

We report the preparation, oxygen reduction reaction (ORR) electrocatalytic activity, and structural transformation of Pt–Ni nanowires (NWs) during potential cycles in the presence and absence of Pt–Ni nanoparticles (NPs). The ORR activity of NWs increases over 25000 potential cycles in the presence of NPs, involving the structural transformation of NWs to branched nanostructures assisted by Ostwald ripening of NPs. This structural transformation is coupled with the surface electronic structural change, as confirmed by in situ X-ray absorption spectroscopy and carbon monoxide stripping voltammetry, leading to catalytic activity improvement and Pt dissolution suppression. Although a similar structural transformation was also observed even in the absence of NPs, greater amounts of Pt were dissolved during potential cycles. These results indicate that the structural transformation is intrinsic to Pt-based NWs but the structural transformation of NWs assisted by Ostwald ripening of NPs is beneficial to suppress the Pt dissolution. The concept of the structural optimization of nanostructured catalysts assisted by Ostwald ripening of NPs under potential cycles will guide us to develop highly active and durable Pt-based electrocatalysts and phase-engineered nanomaterials.