dissolved then 1 l of isopropanol was added with stirring and the resulting mixture was heated wherein it turned black the solution was held under reflux for one hour at 85 u00b0 c and then concentrated by evaporation to a volume of 100 ml the colloidal solution obtained in this way had a ph value of 5 6 and contained 2 g pt l 0 2 wt pt and 2 g l 0 2 wt of the stabilizer kelzan the ratio of pt nanoparticles to stabilizer was thus 1 1 the total chlorine content of the solution was less than 30 ppm the average size of the pt particles was determined by tem and was 2 5 nm an ionomer membrane was catalyzed in the same way as described in example 1 and a membrane with a total platinum loading of 0 2 mg pt cm 2 was produced in a pem single cell very good performance values were obtained when operating with hydrogen air pressureless operation cell voltage 630 mv with a current density of 500 ma cm 2 2 2 g of a solution of bis ethanolammonium hexahydroxoplatinate pt content 9 wt total chlorine content lt 100 ppm from dmc 2 hanau were added dropwise to 1 5 l of fully deionized water in which 0 436 g of gum arabic merck darmstadt and 0 137 g of chromium iii nitrate nonahydrate total chlorine content lt 20 ppm merck had previously been.