Preparation of highly dispersed Pt + Ru alloy clusters and the activity for the electrooxidation of methanol

A new method for the preparation of Pt + Ru binary catalyst has been developed which provides a simple way of obtaining a specific surface area (ca. 80 m2 g−1) more than 3 times larger than that obtained by conventional methods. This method is based on the co-deposition of fine oxides of platinum and ruthenium in atomic scale in a mixed salt solution of these metals followed by reduction with hydrogen bubbling. It was revealed that the binary catalyst prepared by this method forms alloy clusters of their solid solution, in which platinum atoms are replaced by ruthenium atoms on the lattice points of a face-centred cube in the region of Ru/Pt ratios less than 0.75. The supported alloy on carbon black exhibited an extremely high catalytic activity during the electrooxidation of methanol; i.e. ca. 200 mA cm−2 at 0.4 V and a limiting current of more than 1 A cm−2 when Ru/Pt = 1/1. From a comparison of the relationship between the composition of the alloy and the activity with that of an ad-electrode having ruthenium ad-atoms with a well-defined coverage, it was concluded that the composition of the alloy cluster surface is probably the same as that of the cluster bulk.