Mixed colloidal suspensions of reduced graphene oxide and layered metal oxide nanosheets: Useful precursors for the porous nanocomposites and hybrid films of graphene/metal oxide

Homogeneously mixed colloidal suspensions of reduced graphene oxide, or RGO, and layered manganate nanosheets have been synthesized by a simple addition of the exfoliated colloid of RGO into that of layered MnO ₂. The obtained mixed colloidal suspensions with the RGO/MnO ₂ ratio of ≤0.3 show good colloidal stability without any phase separation and a negatively charged state with a zeta (ζ) potential of -30 to -40 mV. The flocculation of these mixed colloidal suspensions with lithium cations yields porous nanocomposites of Li/RGO-layered MnO ₂ with high electrochemical activity and a markedly expanded surface area of around 70-100 m ² g ^-1. Relative to the Li/RGO and Li/layered MnO ₂ nanocomposites (≈116 and ≈167 F g ^-1), the obtained Li/RGO-layered MnO ₂ nanocomposites deliver a larger capacitance of approximately 210 F g ^-1 with good cyclability of around 95-97 % up to the 1000th cycle, thus indicating the positive effect of hybridization on the electrode performances of RGO and lithium manganate. Also, an electrophoretic deposition of the mixed colloidal suspensions makes it possible to easily fabricate uniform hybrid films composed of graphene and manganese oxide. The obtained films show a distinct electrochemical activity and a homogeneous distribution of RGO and MnO ₂. The present experimental findings clearly demonstrate that the utilization of the mixed colloidal suspensions as precursors provides a facile and universal methodology to synthesize various types of graphene/metal oxide hybrid materials.