A Diruthenium-Substituted Polyoxometalate as an Electrocatalyst for Oxygen Generation

Transition metal heteropolyanions have been used to catalyze a variety of organic oxidations but have not previously been used for O₂ generation, despite sharing some structural similarities with dioxoruthenium water-oxidation catalysts. In this study, we report that the di-Ru-substituted polyoxometalate (POM) [Ru₂Zn₂(H₂O)₂(ZnW₉O₃₄)₂]^14- can be used to catalyze the electrochemical generation of O₂. By comparing the behavior of this compound to that observed using a mono-Ru-substituted POM catalyst, we show that adjacent Ru sites are necessary to observe O₂ generation. These observations suggest a reaction pathway involving two Ru-bound oxygen species combining to form O₂ and are consistent with the accepted mechanism of electrochemical oxygen evolution. Finally, analysis of the observed electrode kinetics yields a Tafel slope of roughly 120 mV, which is similar to values reported previously for perovskite anodes.