Nanoscopic Pt-bimetal colloids as precursors for PEM fuel cell catalysts

PEM fuel cell anode catalysts with an improved CO tolerance can be prepared from pre-synthesized bimetallic colloid precursors with particle sizes of 1-2 nm. The particles are supported on Vulcan XC72 and activated by thermal conditioning to remove the stabil izing organic shell. Various routes for colloid synthesis, some using also different organic stabilizers, are explored. NR 4 X-stabilized Pt/Ru- or Pt/Sn-Precursors of sizes below 2 nm and having a narrow particle size distribution are obtained via the co-reduction of platinum, ruthenium and tin salts, respectively, using alkalitriethylhydroborate. Co-reduction of organic metal salts using organoaluminum compounds without addin g any further stabilizer leads to halogen-free, organoaluminum pre-stabilized polymetallic platinum colloids (e.g. Pt 50 Ru 50 /Al-acac-alkyl, particle size 1.2 ± 0.3 nm). The ratio of platinum to second metal in the colloid can be easily adjusted by changing the stoichiometric ratio of the me tal salts. The dispersivity of these colloids can be modified by adding alcohols or suitable surfactants. The size of organoaluminum-stabilize d particles does not change during the thermal conditioning even at high metal loadings (20 wt % metal), avoiding an undesirable particle growth.