Optimization of Synthesis Parameters Employed during Pt Nanoparticle Formation by in situ Reduction

This work is focused on the optimization of the synthesis conditions of a Pt sol phase containing suspended metallic Pt nanoparticles with the primary goal being to produce thin (ca. 1 monolayer) Pt films having the highest possible electroactive surface area per gram. This is gauged here by the surface roughness factor, determined from the magnitude of the Pt electrochemical response in sulfuric acid solution. Two Pt(IV) chloride compounds (H2PtCl6, Na2PtCl6) are shown to be the best Pt precursors, producing stable Pt nanoparticles with an average particle diameter of 1−3 nm. Sodium ethoxide and formic acid are found to be excellent reducing agents of the PtCl6 2- anion, although formaldehyde results in a lower yield of Pt nanoparticles. A ratio of sodium ethoxide to H2PtCl6 of 2:1 and a 72 °C reflux in ethanol between 30 min and 5 h resulted in the highest Pt roughness factor (ca. 8). Transmission electron microscopy analysis has verified that all of the reducing agents produce Pt particles of a similar size and that the higher roughness factors are the result of a higher yield of Pt nanoparticles. The effect of time of storage of Pt sols formed using sodium ethoxide showed that only a minor aging effect is observed over long periods of time, likely minimized by the stabilization offered by PtCl3(C2H4)-, a species formed as a byproduct during the synthesis.