Electrocatalytic epoxidation of cyclooctene to epoxides driven by cobalt-containing polyoxometalate

The electrocatalytic epoxidation directly using water as oxygen source is considered as a sustainable strategy to achieve epoxide production under ambient conditions. However, it is challenging to develop non-noble metal based heterogeneous electrocatalysts for efficient epoxidation with a deep understanding of the structure-activity relationships. In this work, we report a Weakley-polyoxometalate Na10[Co4(H2O)2(PW9O34)2] (Co4P2W18) with high efficiency toward electrocatalytic epoxidation of cyclooctene via directly transfer oxygen atom from water. A significantly higher faradaic efficiency of cyclooctene oxide was achieved over Co4P2W18 than a Keggin type Co substituted polyoxometalate Na5[Co(H2O)PW11O39] (CoPW11) and some other typical electrocatalysts including RuO2, IrO2, and Co3O4 in our system. Experimental results and theoretical calculation indicate that the oxygen atom directly transfers from water for the epoxidation of cyclooctene via the cleavage of OH of pre-adsorbed water as the rate-determined step. Further calculation demonstrates that the water and cyclooctene were adsorbed by Co site and their adjacent terminal oxygen atom during the epoxidation reaction. With the assistance of this terminal oxygen atom for adsorption and as an electron capture center, lower energy barriers for activation of water and cyclooctene are observed on Co4P2W18 than on CoPW11. Our study provides atomic insight into how structure affects catalytic activity, which benefits designing efficient electrocatalysts.