Colloid-chemical properties of ruthenium dioxide in relation to catalysis of the photochemical generation of hydrogen

A colloid of RuO₂, prepared by thermal decomposition of RuCl₃, was characterized with respect to its colloid-chemical properties and assessed as a catalyst for photochemical production of hydrogen. The RuO₂ proved to be unstable towards coagulation, even under conditions of low electrolyte concentration and in the presence of polymers. The sol manifested the same electric double layer characteristics as many other oxide dispersions. The point of zero charge (p.z.c.) in indifferent electrolyte was positioned at pH 5.75.Adsorption of methylviologen (MV²⁺), a commonly used electron relay in photochemical systems, at the RuO₂/solution interface is mainly a result of attractive coulombic interactions (above the p.z.c. of RuO₂). No indications have been found that it adsorbs on RuO₂ under the operational conditions of hydrogen production. In the hydrogen production system, the mass transfer of methylviologen radicals (MV⁺) is a rate-limiting factor. As a function of the methylviologen concentration, the catalytic production of hydrogen passes through a maximum.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.