Preparation and cyclic voltammetric dissolution of core–shell–shell Ag–Pt–Ag nanocubes and their comparison in oxygen reduction reaction in alkaline media

An efficient synthesis of core–shell–shell Ag–Pt–Ag nanocubes using Ag nanocubes as reactants was developed. Ag nanocubes were synthesized as seeds; after (NH3)2Pt(NO2)2 was added in situ, the nanocubes underwent epitaxial growth followed by further Ag deposition to form core–shell–shell Ag–Pt–Ag nanocubes. In this study, the successful determination of the core–shell–shell structures of the Ag–Pt–Ag nanocubes by an electrochemical dissolution process was studied. The Ag dissolution was followed by an electrochemical quartz crystal microbalance technique, and hollow Ag–Pt nanocubes were obtained after the third cycle of a cyclic voltammetric method in 0.5 M H2SO4 electrolyte. Additionally, these Ag–Pt–Ag and Ag–Pt nanocubes were used as electrocatalysts in the alkaline oxygen reduction reaction (ORR). Electrochemical measurements were performed using an ultrathin-film rotating ring-disk electrode (RRDE). The mass activities at −0.1 V (vs. Ag/AgCl; within the kinetic control region) in terms of the currents normalized to the Pt mass for the Ag–Pt–Ag and the Ag–Pt nanocubes were 1.08 × 10−3 and 3.3 × 10−3 mA μg−1, respectively. The data supported by RRDE showed approaching 4 electrons and lower HO2− production over Ag–Pt–Ag nanocubes and Ag–Pt nanocubes, implying that the four-electron pathway governed the ORRs for these two catalysts. After 1000 cyclic tests, Ag–Pt–Ag nanocubes with solid interior displayed superior stability in ORR than hollow Ag–Pt nanocubes.