Polyoxometalate Supported Single Transition Metal Atom as a Redox Mediator for Li-O 2 Batteries.

Keggin-type polyoxometalate (POM) supported single transition metal (TM) atom (TM 1 /POM) as an efficient soluble redox mediator for Li-O 2 batteries is comprehensively investigated by first-principles calculations. Among the pristine POM and four kinds of TM 1 /POM (TM = Fe, Co, Ni, and Pt), Co 1 /POM not only maintains good structural and thermodynamic stability in oxidized and reduced states but also exhibits promising electro(chemical) catalytic performance for both oxygen reduction reaction and oxygen evolution reaction (OER) in Li-O 2 batteries with the lowest Gibbs free energy barriers. Further investigations demonstrate that the moderate binding strength of Li 2- x O 2 ( x = 0, 1, and 2) intermediates on Co 1 /POM guarantees favorable Li 2 O 2 formation and decomposition. Electronic structure analyses indicate that the introduced Co single atom as an electron transfer bridge can not only efficiently improve the electronic conductivity of POM but also regulate the bonding/antibonding states around the Fermi level of [Co 1 /POM-Li 2 O 2 ] ox . The solvent effect on the OER catalytic performance and the electronic properties of [Co 1 /POM-Li 2 O 2 ] ox with and without dimethyl sulfoxide solvent are also investigated.