Heteropolytungstate-assisted fabrication and deposition of catalytic silver nanoparticles on different reduced graphene oxide supports: Electroreduction of oxygen in alkaline electrolyte

The unique feature of Keggin-type dodecatungstosilicate (SiW12O404−) to undergo adsorption on silver surfaces is explored here to fabricate, modify and stabilize silver nanoparticles in acid medium, as well as to link them to different reduced graphene oxide (rGO) substrates: SiO2-doted rGO, carboxylate-derivatized rGO, and conventional rGO (obtained through the chemical reduction method). Upon medium transfer to alkaline electrolyte, the inorganic polyoxometalate-capping-ligand disappears but silver nanostructures remain on rGO supports. The electrocatalytic activity of the resulting systems are probed during the oxygen reduction reaction (ORR). It is apparent from XRD data that silver is crystalline in nature and, particularly in a case of SiO2-doted rGO supports, metallic silver nanocrystals have face-centered-cubic structures enriched with high-index Ag(111) facets known to facilitate ORR. Functionalization of graphene with SiO2 seems to provide an efficient way to keep the nanosheets of graphene exfoliated thus facilitating unimpeded flux of reactants and making the system easily accessible for intercalation with catalytic Ag. Silver nanoparticles supported onto SiO2-doted rGO are relatively the most active toward ORR when examined under rotating ring disk conditions in terms of the observed highest catalytic current density, the most positive ORR onset potential, and the lowest percent formation of the H2O2 reaction intermediate.