Pt–Ag/C catalyst for methanol oxidation and alcohol tolerant cathode in different electrolytes

Abstract

Pt–Ag/C catalyst was prepared by sonication to evaluate its catalytic activity for the oxygen reduction (ORR) and methanol oxidation reactions (MOR). The synthesized material was characterized by X-ray diffraction (XRD), elemental disperse spectroscopy (EDS), scanning (SEM) and transmission electron microscopy (TEM) techniques. Cyclic voltammetry, linear voltammetry and chronoamperometry studies were also carried out in acid and alkaline electrolytes with different methanol concentrations (0.0, 0.3 and 0.5 M). Structural properties and elemental composition of bimetallic samples were analyzed by XRD and EDS. According to TEM results, Pt–Ag nanoparticles exhibited a form of spherical agglomerates with poor distribution on carbon. Methanol oxidation reaction (MOR) on Pt–Ag/C in alkaline electrolyte revealed five folds greater activity than in acid medium. Moreover, Pt–Ag/C has exhibited excellent properties as tolerance cathode in acid medium, showing that the activity was not affected with the presence of methanol. However, in alkaline medium the Pt–Ag/C kinetics, as cathode catalyst, was drastically affected by the presence of methanol, presenting a negative onset potential shift, which increased with methanol concentration. The Ag presence and formed Ag-oxide modified the tolerance of methanol for ORR in acid electrolyte and promoted the catalytic activity of Pt for MOR in alkaline electrolyte. Pt/C sample was synthesized and tested at the same conditions for comparison purposes.