Reduction of graphene oxide using Salvia Officinalis plant extract and its utilization for Li-O₂ batteries

The significance of reduced graphene oxide (rGO) as an electrode material has been widely explored in lithium‑oxygen batteries (LOBs) owing to its extensive surface area, excellent electrical conductivity, good mechanical strength, and chemical stability. However, depending on the synthesis procedures and thermal treatments, the rGO structure might have variable structural and chemical features such as the number of layers, functional groups, and defect structure, affecting the electrochemical activity of the electrodes. In recent years, researchers have attempted to produce rGO sheets by reduction of graphene oxide (GO) for different purposes. Several methods have been reported to obtain rGO, such as unzipping of carbon nanotubes, epitaxial growth, chemical vapor deposition, electrochemical exfoliation of graphite, and chemical reduction of GO. Herein, a green strategy was used to synthesize reduced graphene oxide nanosheets by utilizing extract of Salvia Officinalis leaves. The natural reducing agent was compared with sodium borohydride (NaBH₄) and hydrazine (N₂H₄) as potential toxic reducing agents. Graphene oxide was produced by the modified hummers process and successfully reduced by Salvia O. extract due to the presence of active biomolecules in the plant, which act as reducing agents. The proposed method avoids the use of hazardous and expensive chemicals. The as-prepared rGO materials were applied as cathode materials for LOBs, and their electrochemical performances were evaluated. The results exhibited that the electrode GO reduced by Salvia extract delivered a capacity of 4320 mAh g⁻¹, while rGO reduced by hydrazine and NaBH4 offered specific capacities of 3840 mAh g⁻¹ and 3210 mAh g⁻¹, respectively.