Silver nanoparticles-anchored reduced graphene oxide (Ag-RGO) is prepared by simultaneous reduction of graphene oxide and Ag(+) ions in an aqueous medium by ethylene glycol as the reducing agent. Ag particles of average size of 4.7 nm were uniformly distributed on the RGO sheets. Oxygen reduction reaction (ORR) is studied on Ag-RGO catalyst in both aqueous and non-aqueous electrolytes by using cyclic voltammetry and rotating disk electrode techniques. As the interest in non-aqueous electrolyte is to study the catalytic performance of Ag-RGO for rechargeable Li-O2 cells, these cells are assembled and characterized. Li-O2 cells with Ag-RGO as the oxygen electrode catalyst are subjected to charge-discharge cycling at several current densities. A discharge capacity of 11 950 mA h g(-1) (11.29 mA h cm(-2)) is obtained initially at low current density. Although there is a decrease in the capacity on repeated discharge-charge cycling initially, a stable capacity is observed for about 30 cycles. The results indicate that Ag-RGO is a suitable catalyst for rechargeable Li-O2 cells.

Gold nanoparticles decorated reduced graphene oxide (Au-RGO) catalyst for O 2 electrode is prepared by in situ reduction of Au 3+ ions and graphene oxide dispersed in water. The Au nanoparticles are uniformly distributed on the two-dimensional RGO layers. Li-O 2 cells assembled in a non-aqueous electrolyte using Au-RGO catalyst exhibit an initial discharge capacity as high as 5.89 mA h cm À2 (5230 mA h g À1 ) at a current density of 0.1 mA cm À2 . The voltage gap between the charge and discharge curves is less for Li-O 2 (Au-RGO) cell in comparison with Li-O 2 (RGO) cell. The Li-O 2 (Au-RGO) cells are cycled over about 120 charge-discharge cycles. The results suggest that Au-RGO is a promising catalyst for rechargeable Li-O 2 cells.

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Polypyrrole (PPY) is grown on reduced graphene oxide (RGO) and the composite is studied as a catalyst for O 2 electrode in Li-O 2 cells. PPY is uniformly distributed on the two dimensional RGO layers. Li-O 2 cells assembled in a non-aqueous electrolyte using RGO-PPY catalyst exhibit an initial discharge capacity as high as 3358 mAh g −1 (3.94 mAh cm −2 ) at a current density of 0.3 mA cm −2 . The voltage gap between the charge and discharge curves is less for Li-O 2 (RGO-PPY) cell in comparison with Li-O 2 (RGO) cell. The Li-O 2 (RGO-PPY) cell delivers a discharge capacity of 550 mAh g −1 (0.43 mAh cm −2 ) at a current density of 1.0 mA cm −2 . The results suggest that RGO-PPY is a promising catalyst of O 2 electrode for high rate rechargeable Li-O 2 cells.

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