Galvanic displacement synthesis

Fig. 4.3 Schematic representation of galvanic displacement synthesis for DENs.

Since the first report of dendrimer-encapsulated Cu nanoparticles [15], several types of mono and bi-metallic DENs have been prepared. DEN synthesis has been recently reviewed [9,16], so only the synthesis of bimetallic DENs is described here. Bimetallic DENs can be prepared by one of three methods co-complexation of metal salts, galvanic displacement, and sequential reduction. Several bimetallic systems have already been prepared inside PAMAM dendrimers Table 1 summarizes the current literature and synthetic methods employed. 

Galvanic displacement method is also often used for synthesizing catalysts. By this method, low Pt-content electrocatalysts can be obtained. For example, a carbon-supported core—shell structured electrocatalyst with bimetallic IrNi as the core and platinum monolayer as the shell has been successfully synthesized using this method. In this synthesis, IrNi core supported on carbon was first synthesized by a chemical reduction and thermal annealing method and a Ni core and Ir shell structure could be formed finally. The other advantage of this method is that the Ni can be completely encased by Ir shell, which will protect Ni dissolve in acid medium. Secondly, IrNi PtML/C core—shell electrocatalyst was prepared by depositing a Pt monolayer on the IrNi substrate by galvanic displacement of a Cu monolayer formed by under potential deposition (UPD). 

An important factor affecting the performance of DMFCs is the kinetics of catalyst. Platinum (Pt/C) is the most effective catalyst for oxygen reduction reaction but it is not selective towards ORR in presence of methanol. The addition of yttrium to Pt increases the ORR activity and are promising ORR electrocatalyst [207]. Carbon supported PtY(OH)3 hybrid catalyst are developed with dynamic spillover of metal oxide [208]. Recently, catalyst for DMFC Pt Pd/C NP was prepared by the galvanic displacement reaction between Pt and Pd. A simple synthesis strategy was followed to prepare carbon based [209] and carbon-supported Pd nanostructure [190]. A higher methanol tolerance of Pt Pd/C with less Pt content than Pt/C suggests that it is potential alternative cathode electrocatalyst for DMFCs [190]. 

Song, Y. Y, W. Z. Jia, Y. Li et al. 2007. Synthesis and patterning of Prussian blue nanostructures on silicon wafer via galvanic displacement reaction. Adv. Funct. Mater. 17 2808-2814. 

Yuan J, Lai Y, Duan J, Zhao Q, Zhan J (2012) Synthesis of a p-cyclodextrin-modified Ag film by the galvanic displacement on copper foil for SERS detection of PCBs. J Coll Interface Sci 365 122-126... 

Dendrimer-templated synthesis of metal nanoparticles is a powerful technique and many metal DENs can be synthesized. However, the approach cannot be used to synthesize metal nanoparticles whose precursors (metal ions) have weak interactions with the dendrimers. For certain metal ions, such as Ag% another technique was developed based on galvanic redox displacement [68]. Using the galvanic redox displacement technique, Cu DENs were mixed with Ag. Since the standard reduction potential of Ag+ is more positive than Cu, Ag will be reduced to form Ag(0), and Cu(0) will be oxidized to Cu. Therefore, Cu DENs will be converted to Ag DENs using this technique. The conversion of Cu DENs to Au, Pt, or Pd DENs has also been demonstrated using the galvanic redox displacement technique [68]. 

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