Synthesis of Pt-Bi/carbon electrodes by reduction method for direct methanol fuel cell

Pt-Bi/C catalysts supported on carbon black with various Pt/Bi ratios were synthesized by a reduction method. Chloroplatinic acid hydrate (H ₂PtCl ₆ · xH ₂O) and bismuth (III) nitrate pentahydrate (Bi(NO ₃) ₃ · 5H ₂O) were used as precursors for Pt and Bi, respectively. Before loading metal on carbon, heat treatment and pretreatment of carbon black in an acidic solution was conducted to enhance the degree of dispersion. The physical property of the synthesized catalysts was investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The XRD pattern of untreated Pt-Bi/C catalyst showed BiPt and Bi ₂Pt peaks in addition to Pt peaks. These results imply that Bi atoms were incorporated into the Pt crystal lattice by Pt-Bi alloy formation. The catalytic activity for methanol oxidation was measured using cyclic voltammetry in a mixture of 0.5 M H ₂SO ₄ and 0.5 M CH ₃OH aqueous solution. The addition of proper amount of Bi was found to significantly improve catalytic activity for methanol oxidation. The catalytic activity for methanol oxidation was closely related to the stability between electrode and electrolyte. In order to investigate the stability of catalysts, chronoamperometry analysis was carried out in the same solution at 0.6 V.