Facile synthesis of Pd–Ir bimetallic octapods and nanocages through galvanic replacement and co-reduction, and their use for hydrazine decomposition

This article describes a facile synthesis of Pd–Ir bimetallic nanostructures in the forms of core–shell octapods and alloyed nanocages. The success of this synthesis relies on the use of Pd nanocubes as the sacrificial templates and interplay of two different processes: the galvanic replacement between an Ir precursor and the Pd nanocubes and the co-reduction of Pd2+ and Ir3+ by ethylene glycol. The galvanic replacement played a dominant role in the initial stage, through which Pd atoms were dissolved from the side faces whereas Ir atoms were deposited at the corner sites to generate Pd–Ir core–shell octapods. As the concentration of Pd2+ in the reaction mixture was increased, co-reduction of Pd2+ and Ir3+ occurred in the late stage of synthesis. The resultant Pd and Ir atoms were deposited onto the octapods while the Pd atoms in the interiors continued to be etched away due to the galvanic replacement, finally leading to the formation of Pd–Ir alloyed nanocages. The octapods and nanocages were then evaluated as catalysts for the selective generation of hydrogen from the decomposition of hydrous hydrazine. The nanocages exhibited better selectivity for hydrogen generation than octapods (66% versus 29%), which can be attributed to the presence of an alloyed, porous structure on the surface.