Influence of different buffer solutions on the performance of anodic Pt-Ru/C nanoparticle electrocatalysts for a direct methanol fuel cell

This research aims to improve the activity of Pt-Ru nanoparticle electrocatalysts and thus, to lower the catalyst loading in anodes for methanol electrooxidation. The direct methanol fuel cell (DMFC) anodic Pt-Ru/C nanoparticle electrocatalysts were prepared using a chemical reduction method. The pH values of the reductive solutions were adjusted by different buffer solutions of CH₃COONa-NaOH, C₆H₅Na₃O₇-NaOH, and Na₂CO₃-NaHCO₃, respectively. The performance of the nanoparticle electrocatalysts were examined by cyclic voltammetry, chronoamperometry, and amperometric i-t curves using a glassy carbon working electrode in a solution of 0.5 mol L^-1 CH₃OH and 0.5 mol L^-1 H₂SO₄. The structures and micro-morphology of the Pt-Ru/C nanoparticles were determined and observed by X-ray diffraction (XRD) and transmission electron microscopy. XRD analysis showed that all of catalysts exhibited face-centered cubic (fcc) structures. No diffraction peaks indicated the presence of either pure Ru or Ru-rich hexagonal close packed (hcp) phase. The size of the Pt-Ru/C nanoparticles prepared with a C₆H₅Na₃O₇-NaOH solution was relatively small ∼4.3 nm. Its size distribution in carbon was more homogeneous. The electrochemical active measurements results showed that the catalytic activity and the stability of Pt-Ru/C nanoparticle electrocatalyst prepared with a C₆H₅Na₃O₇-NaOH solution for methanol electrooxidation was higher than that from the other solutions due to the citrate complexation stabilizing effect and a competing adsorption effect.