A layered sodium manganese oxide, Na_0.6MnO₂, stable at temperatures above 800 °C, was synthesized by using a sol–gel method that employs Mn(acac)₃ (ac = acetylacetonate), Na₂CO₃ and propionic acid to form the resin framework. This layered bronze possesses a hexagonal, P2-type structure, in which the distortion associated with Mn³⁺ is hardly perceptible. It reacts slowly, though reversibly, with atmospheric moisture, which causes the interlayer spacing in the structure to increase by ca. 2.5 Å, through intercalation of water molecules into the interlayer gap occupied by Na⁺ ions. The anhydrous material was tested as a cathode in sodium cells. Although the electrochemical intercalation of Na⁺ occurs in two steps, the host retains its main structural features, with a slight tendency in the interlayer spacing to contract as the sodium content increases. The similarity between the discharge and charge profiles of the first cycles reveals a quasi-reversible nature in the intercalation process and that the cell can deliver a constant specific capacity of ca. 140 A h kg⁻¹ at 0.1 mA cm⁻² when cycled in a voltage window of 3.8–2.0 V. However, the continuous strains and distortions resulting from the insertion and extraction of Na⁺ ions cause the host structure to gradually collapse and yield an amorphous material after the first eight cycles. This leads to a progressive reduction of the cell capacity, irrespective of the specific voltage window used.

Graphene nanosheets (GNS) were prepared from graphitic oxide (GO) in two different ways: (a) thermal exfoliation at different temperatures; and (b) wet chemistry, using aqueous N₂H₄ and KBH₄ as reducing agents. Irrespective of the synthetic method used, the materials exhibited a high irreversible capacity and strong polarization in their charge curves, when used in a Li-ion battery. The GNS synthesized with N₂H₄ exhibited the best performance. Thus, at 149 mA g⁻¹ the average specific capacity delivered was ca. 600 mA h g⁻¹ after 100 cycles. On the other hand, the worst performance, irrespective of rate, was that of GNS synthesized with KBH₄ and the thermal GNS obtained at 800 °C. The physical and chemical analyses allowed various parameters to be derived for correlation with the electrochemical properties. Unfortunately, no clear-cut correlation was apparent. A comparison with reported data revealed that no correlation appears to exist with physical and chemical properties that allows a simple strategy for tailoring an effective graphene anode to be designed.

Graphene-based materials are highly interesting in virtue of their excellent chemical, physical and mechanical properties that make them extremely useful as privileged materials in different industrial applications. Sonochemical methods allow the production of low-defect graphene materials, which are preferred for certain uses. Graphene nanosheets (GNS) have been prepared by exfoliation of a commercial micrographite (MG) using an ultrasound probe. Both materials were characterized by common techniques such as X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All of them revealed the formation of exfoliated graphene nanosheets with similar surface characteristics to the pristine graphite but with a decreased crystallite size and number of layers. An exhaustive study of the particle size distribution was carried out by different analytical techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and asymmetric flow field flow fractionation (AF4). The results provided by these techniques have been compared. NTA and AF4 gave higher resolution than DLS. AF4 has shown to be a precise analytical technique for the separation of GNS of different sizes.