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 stabilizing organic shell. Various routes for c olloid synthesis, some using also different organic stabilizers, are explor ed. NR4X-stabilized Pt/Ru- or Pt/Sn-Precursors of sizes below 2 nm and havi ng a narrow particle size distribution are obtained via the co-reduction of platinum, ruthenium and tin salts, respectively, using alkalitriethylhydro borate. Go-reduction of organic metal salts using organoaluminum compounds without adding any further stabilizer leads to halogen-free, orgartoaluminu m pre-stabilized polymetallic platinum colloids (e.g. Pt50Ru50/Al-acac-alky l, 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 metal salts. The dispersivity of these colloids can be modified by addi ng alcohols or suitable surfactants. The size of organoaluminum-stabilized particles does not change during the thermal conditioning even at high meta l loadings (20 wt % metal), avoiding an undesirable particle growth.