Electrochemical quartz crystal microbalance studies on specific adsorption of nanoparticle stabilizers on platinum surface

Abstract

• Phosphinate reduces mass change of adsorbate film on Pt at the double layer region. • Phosphinate suppresses reduction of Pt to zero-valent and growth of metal particles. • Citrate adsorbs on Pt and increases adsorption strength of coadsorbed oxygen. • Citrate inhibits Cu electrodeposition on Pt while phosphinate has a minor effect. • Suberate adsorbs more than citrate on Pt to prevent nanoparticle aggregation. Phosphinate and citrate ions are effective stabilizers for aqueous phase synthesis of platinum-based nanoparticles. In the present study, specific adsorption/desorption of stabilizers on platinum surface was investigated using an electrochemical quartz crystal microbalance (EQCM). Cyclic voltammetry combined with EQCM revealed that phosphinate ion reduces mass change of adsorbate film on Pt at the double layer region and it was oxidized by water and oxygen species producing anodic current above 0.2 V vs. Ag/AgCl. Phosphinate stabilizes positively charged platinum species rather than metallic species, which leads to size reduction of metal nanoparticles. Density Functional Theory calculation indicated that phosphinate adsorbs on Pt via two oxygen atoms (though coadsorbed water might change the structure) and the interaction strength increases with increasing positive charge on Pt surface. Meanwhile, citrate increased adsorption strength of oxygen on Pt in a weakly acidic condition. Electrodeposition of copper on Pt was significantly suppressed in the presence of citrate. The capping effect of citrate and oxygen on metallic surface helps dispersing nanoparticles.