Alkyne-functionalized palladium nanoparticles: Synthesis, characterization, and electrocatalytic activity in ethylene glycol oxidation

1-Octyne-stabilized palladium nanoparticles (PdHC8, core dia. 2.50 ± 0.28 nm) were prepared by a simple reduction procedure. FTIR studies showed that the self-assembly of 1-octyne onto the Pd nanoparticle surfaces involved the effective breaking of the terminal HC bonds and the formation of Pd–vinylidene interfacial linkages by a tautomeric rearrangement process. With this conjugated metal–ligand interfacial bond, the nanoparticles exhibited unique photoluminescence properties that were analogous to those of diacetylene derivatives. Furthermore, thermogravimetric analysis showed that there were about 150 ligands per nanoparticle, with an average footprint of ca. 13 Å2 per capping ligand on the nanoparticle surface, consistent with a head-on configuration of the alkyne ligands on the Pd surface. Interestingly, the PdHC8 nanoparticles exhibited apparent electrocatalytic activity in the oxidation of ethylene glycol in alkaline media that was about twice that of commercial Pt/C, as manifested in cyclic voltammetric and chronoamperometric studies. Such an apparent improvement of the electrocatalytic activity was most probably ascribed to the partial removal of the alkyne capping ligands whereby the remaining molecules provided a relatively hydrophobic chemical environment and hence facilitated the removal of water generated from the oxidative dehydration reaction of ethylene glycol. Additionally, the enhanced electron density within the Pd metal cores as a result of the intraparticle charge delocalization between the particle-bound acetylene moieties might also facilitate the formation of PdC bonds in Pd-[C2H3(OH)2]ads, which was presumed to be the rate-determining step in ethylene glycol oxidation on Pd surfaces.

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