Towards the Construction of a Complete Cyclic Water Decomposition System, Design and Operation of an Oxygen Producing Half Cell

Oxygen is generated when aqueous solution of iron (III) tris(2,2′‐bipyridyl), Fe(bipy) , are brought in contact with catalytic amounts of powdered or colloidal RuO2. The oxygen yield depends strongly on the pH, reaching a maximum between pH 7 and 8 where it corresponds to the stoichiometry of the reaction: equation image The rate of the reaction is so fast that it occurs practically upon dissolution of Fe(bipy) in the aqueous phase. In acidic media (pH 4), no O2 evolution is observed. Instead, Fe(bipy) is converted to an intermediate which in the presence of RuO2 yields O2 upon neutralization. The pH profile of the O2 evolution occuring upon illumination of Ru(bipy) in the presence of the cobalt complex [Co(NH3)5Cl]2+ was also investigated. The surprisingly low energy losses (160 mV) in reaction (1) makes the construction of four quanta water splitting systems feasible.