Polyoxometallate-stabilized Pt-Ru catalysts on multiwalled carbon nanotubes: influence of preparation conditions on the performance of direct methanol fuel cells
A novel catalyst, polyoxometallate-stabilized platinum-ruthenium alloy nanoparticles Supported on multiwalled carbon nanotubes (Pt-Ru-PMo12-MWNTs), was synthesized by a microwave-assisted polyol process. The effects of microwave reaction time, microwave reaction power, and pH value of the reaction solution on the electrocatalytic properties of Pt-Ru-PMo12-MWNTs catalysts were also investigated. The polyoxometallate (PMo12) formed a self-assembled monolayer on the surface of the Pt/Ru nanoparticles and MWNTs, which effectively prevented the agglomeration of Pt. Ru nanoparticles and MWNTs, due to the electrostatic repulsive interactions between the negatively charged PMo12 monolayers. Energy dispersive spectroscopy examination and electrochemical measurements showed that the loading content of Pt/Ru and their electrochemical activity vary with the synthesis conditions, such as pH, reaction time, and microwave power. It was found that the a Pt-RU-PMo12-MWNTs electrocatalyst with high Pt loading content, small crystallite size, and good electrocatalytic activity could be synthesized using a long reaction time, intermediate microwave power, and a pH value of 7. The electrocatalysts obtained were characterized using X-ray diffraction, and scanning and transmission electron microscopy. Their electrocatalytic properties were also investigated by using the cyclic voltammetry technique.