Fabrication of polyoxometallate-modified gold nanoparticles and their utilization as supports for dispersed platinum in electrocatalysis

Abstract

The usefulness of Keggin-type anions (PMo 12O 40 3−) as both reducing, capping and activating agents during synthesis of polyoxometallate-modified gold nanoparticles is demonstrated here. Fabrication of gold nanoparticles stabilized with monolayer-type films of inorganic polyoxometallates (e.g. phosphododecamolybdates), Au-PMo 12, was achieved by treating an aqueous solution of gold precursor (HAuCl 4) with a solution of the partially reduced heteropolyblue molybdate. The choice of temperature strongly affected morphology and size of the resulting Au nanoparticles. The presence of strongly adsorbed molybdate-agents on surfaces of gold nanoparticles was evident from the independent infrared (FTIR by reflectance) and voltammetric experiments. Interfacial polymolybdate anions on Au prevent the particle agglomeration and support formation of the stable colloidal Au-PMo 12 solutions. They are colored due to existence of the plasmonic effect. The Au-PMo 12 nanoparticles typically had 30–40 nm diameters, and they were used as supports or carriers for dispersed catalytic platinum nanoparticles (of ca. 7–8 nm diameters). Polyoxometallates (PMo 12O 40 3−) existing on gold surfaces could also interact with neighboring platinum centers thus acting as “linking” agents facilitating dispersion of Pt nanoparticles. Further, the phosphomolybdate adsorbates (on Au supports) are also likely to activate Pt sites (e.g. by providing reactive hydroxy groups) towards more efficient electrocatalytic oxidation of ethanol both under voltammetric and chronoamperometric conditions.