An active contribution: The specific capacitance of carbon‐based supercapacitors can be significantly improved by the addition of an electrochemically active compound (hydroquinone) to the supporting electrolyte. The strong contribution of the redox‐active electrolyte to the pseudocapacitance of the system results in the largest capacitance values obtained for an activated carbon‐based supercapacitor.

The mechanisms involved in the storage of energy in carbon-based supercapacitors modified by the addition of an electrochemically active compound (quinone/hydroquinone, Q/HQ) into the electrolyte (H2SO4) are investigated. Besides the charging of the double-layer characteristic of carbon materials, galvanostatic cycling experiments performed on each electrode revealed a battery-type behavior in the anode and a pseudocapacitive hydrogen electrosorption process in the cathode as a consequence of an asymmetric split of voltage between the electrodes after the incorporation of HQ. Both the hydrogen electrosorption and Q/HQ redox reactions were studied in depth from the cyclic voltammograms obtained for both electrolytes in a three-electrode cell. An outstanding specific capacitance value of 5017 F g–1 was attained by the anode due to the development of the quinoid redox reactions on its surface. Meanwhile, the cathode capacitance also increased significantly with respect to the value obtained by the supercapacitor without HQ (from 290 to 477 F g–1). As a result of the concurrence of all these mechanisms of energy storage, the energy density of the HQ-containing SC is significantly greater than that of the original SC (30.6 W h kg–1 vs 10.1 W h kg–1).

We prepared a series of graphene-like materials by thermal exfoliation/reduction of a graphite oxide (GO) at temperatures between 127ºC and 2400ºC. The extent of the exfoliation and reduction of the GO at different temperatures, as well as the impact on the resultant graphene-like materials (TRGs), were studied through their chemical/structural characterization. The main oxygen loss was observed at 127ºC during the blasting of the GO, which produced its exfoliation into monolayer functionalized TRG with hydroxyl groups and minor amounts of epoxy and carboxyl groups. Above 600ºC, the reduction continued smoothly, with oxygen and hydrogen loss and the conversion of hybridized carbon atoms from sp 3 into sp 2 . 1000ºC appears to be a critical temperature for the efficiency of the reduction process, as the resulting TRG contained less than 2% oxygen and 81.5% sp 2 -carbon atoms. The materials obtained at 2000ºC and 2400ºC were almost oxygen-free and the layers exhibited a dramatic restoration of the pristine graphite structure, as confirmed by the increase in the average size of the sp 2 -domains. The typical * Corresponding author: Fax. + 34 985 29 76 62; E-mail: rosmenen@incar.csic.es (Prof. R. Menéndez) 2 disordered stacking of TRGs increases with temperature, although they can be dispersed yielding monolayers at 127 and 300°C and stacks of up to 4-6 layers above 1000°C, as determined by AFM.

Graphene materials containing different functional groups were prepared from a natural graphite, by means of two different oxidation methods (Hummers and Brodie). It was observed that the differences in the structure of the resultant graphite oxides (GOs) greatly affect the structure of the graphenes resulting from their thermal exfoliation/reduction. Although the oxidation of the graphite was more effective with the modified Hummers method than with Brodie´s method (C/O of 1.8 vs 2.9, as determined by XPS), the former generated a lower residual oxygen content after thermal exfoliation/reduction and a better reconstruction of the 2D graphene structure (with fewer defects). This is explained by the presence of conjugated epoxy and hydroxyl groups in the GO obtained by Brodie´s method, which upon thermal treatment, lead to the incorporation of oxygen into the carbon lattice preventing its complete restoration. Additionally, graphene materials obtained with Brodie´s method exhibit, in general, a smaller sheet size and larger surface area.

The effect of the parent graphite on the structure of graphene oxide (GO) is investigated using high purity graphites with a uniform crystallite size. Our results provide direct evidence of how the size of the graphite crystal affects the oxidation process and the functionality and sheet size of the resulting GO. The important role of the crystal boundaries in the graphite with smaller crystallites is confirmed by the smaller size of the GO sheets obtained and also by the presence of carboxylic groups, located at the edges of the sheets. However, functionalization in the graphite with larger crystals mainly occurs in the vicinity of basal plane defects, as evidenced by the larger number of epoxy groups. Thus, this study leads to a better understanding of the oxidation process of graphite and provides a way to produce GOs suitable for different applications.