Oxygen evolution from water oxidation on molecular catalysts confined in the nanocages of mesoporous silicas

Abstract

Here, we report that the water oxidation activity can be significantly increased by confining ruthenium molecular catalysts, such as Ru^II(bda)(pic)₂, in the nanocage of SBA-16. The TOF of Ru^II(bda)(pic)₂ confined in the nanocage increased from 1.2 to 8.7 s⁻¹ by simply increasing the number of Ru^II(bda)(pic)₂ molecules from one to seven in each nanocage, which is direct evidence for the “cooperative activation” mechanism involved in a binuclear reaction pathway for water oxidation reactions. The TOF of Ru^II(bda)(pic)₂ confined in the nanocage can be as high as two times that of the homogeneous Ru^II(bda)(pic)₂ due to the enhanced “cooperative activation” in the limited space of nanocages. Moreover, preliminary kinetic studies suggest that the stability of the molecular catalysts can be greatly improved after confinement in the nanocage. This strategy not only provides a new strategy for the preparation of highly efficient solid-hosted catalysts for water oxidation, but also gives direct evidence for the oxygen evolution mechanism.