Effect of pH on PtRu electrocatalysts prepared via a polyol process on carbon nanotubes

This paper reports a study on the pH effects on the PtRu nanoparticles synthesized in a polyol process that were deposited on carbon nanotubes (CNTs) by reducing metal salts using ethylene glycol at various pHs. It was found that the nanoparticle size, composition, and catalytic activity all were sensitive to pH. The nanoparticles decreased in size as the preparation pH increased from 1.6 to 10.0, with the largest size at 2.47 nm and the smallest at 1.13 nm. An exception was found for pH at 0.7, which resulted in an average size of only 1.01 nm. Preparation pH was found to affect polyol reaction mechanisms, which are believed to be dominated by direct metal reduction at low pH and by both direct metal reduction and hydroxide reduction at high pH. However, at high pH the reactions were limited by hydroxide reductions, and longer reaction durations were needed to fully deposit the metals. To study the pH effect on the electrochemical activity of the catalysts, CO stripping techniques were used to determine peak potentials and active surface areas. Together with cyclic voltammetry in the electro-oxidation of methanol, it was found that the catalyst prepared at pH 8.4 has the best performance.