Electrochemical synthesis of bimetallic Cu-Cd nanoparticles via sequential electrodeposition and co-electrodeposition and involved alloy formation

It is well known that bimetallic nanoparticles exhibit unique properties that allow their use in a wide range of specific purposes, which depend mainly on the final morphology and composition of the deposits obtained from the preparation method used. In that sense, the electrochemical methods become a promising strategy to generate different types of structures, by selecting appropriately the processing variables. For that reason, a comparative analysis of the synthesis of bimetallic Cu-Cd nanoparticles using sequential electrodeposition and co-electrodeposition was performed. In the first method, metal deposits are prepared sequentially, by potentiostatic pulses applied from different solutions containing the individual metal ions, while the co-deposition method was implemented with both constituents provided from the same solution. Scanning electron microscopy images of the deposits prepared by sequential deposition of Cu, followed by Cd, showed flower-like structures, presenting an appreciable symmetry. The co-deposited crystals also showed a greater number of smaller nanoparticles and achieved a higher coverage percentage. Anodic linear sweep voltammetry analysis of the Cd-Cu nanoparticles/highly oriented pyrolytic graphite systems revealed different peaks associated with the dissolution of Cd and Cu deposits as well as peaks related to different alloyed phases. In the bimetallic system formed by sequential deposition, the Cu₅Cd₈ and Cu₄Cd₃ phases were identified, while in that obtained by co-deposition, the CuCd₃ and Cu₄Cd₃ phases were evidenced, showing a greater tendency towards alloying. These alloyed phases were also confirmed by constant-current stripping experiments. The formation of a Cd-Cu alloy could also be inferred by Density Functional Theory calculations.