A graphene doped carbon xerogel was synthesized by simply replacing the water (solvent) by an aqueous well-dispersed graphene oxide stable suspension in the precursor mixture used for the synthesis of the organic xerogel. During the carbonization of the organic xerogel, the graphene oxide sheets are reduced to graphene, which is embedded and well dispersed within the carbon xerogel matrix. Only a small minimum amount of graphene oxide is necessary to interconnect the graphene sheets throughout the carbon xerogel. This material has both a high porosity and an excellent electrical conductivity so that, when used as electrode in aqueous supercapacitors at high current density, it provides them with 25% more capacitance and 100% more power than the undoped carbon xerogels. The synthesis conditions, characteristics of the carbons and how these affect the electrical conductivity and performance of the materials in the supercapacitors are discussed.

Please cite this article as: Rodriguez-Pastor, I., Ramos-Fernandez, G., Varela-Rizo, H., Terrones, M., Martin-Gullon, I., Towards the understanding of the graphene oxide structure: How to control the formation of humic-and fulviclike oxidized debris, Carbon (2014), doi: http://dx.doi.org/10.1016/j.carbon. 2014.12.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract Former structural models of graphene oxide (GO) indicated that it consists of graphenelike sheets with oxygen groups, and no attention was paid to the resulting sheet size. We now provide evidence of the complex GO structure consisting of large and small GO sheets (or oxidized debris). Different oxidation reactions were studied. KMnO 4 derived GO consists of large sheets (20-30 wt. %), and oxidized debris deposits, which are formed by humic-and fulvic-like fragments. Large GO sheets contain oxygen groups, especially at the edges, such as carbonyl, lactone and carboxylic groups. Humic-like debris consists of an amorphous gel containing more oxygenated groups and trapped water molecules. The main desorbable fraction upon heating is the fulvic-like material, which contains oxygen groups and fragments with high edge/surface ratio. KClO 3 in HNO 3 or the Brodie method produces a highly oxidized material but at the flake level surface only; little oxidized debris and water contents are found. It is noteworthy that an efficient basal cutting of the graphitic planes in addition to an effective intercalation is caused by KMnO 4 , and the aid of NaNO 3 makes this process even more effective, thus yielding large monolayers of GO and a large amount of humic-and fulvic-like substances.

A series of resorcinol formaldehyde based carbon xerogels were synthesized under identical conditions using different graphene oxide loads. The gelification reaction was carried out using a stable aqueous suspension of graphene oxide, yielding organic gels with graphene oxide concentrations ranging from 1.2 to 2.5%. After the carbonization, xerogels with medium surface area (650 m 2 /g) and a highly improved electrical conductivity were obtained. Specific capacitance of 120 F/g of one electrode at very high scan rate of 500 mV/s were achieved, as well as power densities above 30 kW/kg, which is a significant improvement of 180% with respect to the pristine xerogels. Carbonized xerogels were further steam activated to yield activated carbon xerogels with surface areas of up to 1800 m 2 /g. The use of activated xerogels improves slightly the specific capacitance at low scan rates only, and there is a sharp decrease above 20 mV/s, resulting in a worse performance than graphene oxide doped carbonized xerogels. The electrical conductivity of the graphene oxide-doped carbon xerogels decreases upon activation, which means that the influence of the electrical conductivity on a carbon xerogel is greater than its specific surface area, which it is is the first time it is observed for porous carbons.

The present study deals with the influence of graphene oxide functional groups on their ability to reinforce an epoxy resin when forming carbon fiber composites. Composites were processed through the direct vacuum infusion of the doped resin into carbon fiber fabrics. We used graphene oxide nanosheets with two different chemical characters: as‐produced graphene oxide, with a high oxygen content and acid character, and a simple ammonia base‐washed graphene oxide, which to a great extent removes the oxidative debris or highly oxidized fulvic‐like entities, resulting in an average lower oxygen content and cleaner surface sheets than as‐produced graphene oxide. Base‐washed graphene oxide performed considerably better in both tensile and mode‐I interlaminar properties of carbon fiber composites. The fracture energy required for the onset of mode I interlaminar fracture toughness was enhanced 31% when using as‐produced graphene oxide and 60% when using base‐washed graphene oxide by adding 0.2 wt% only. More interestingly, base‐washed graphene oxide produces a higher delamination resistance along the entire range of crack growth. The effect of adding graphene oxide with a cleaner surface and lower oxygen surface chemistry allows direct chemical bonding matrix‐graphene when the resin is curing, promoting a better interface fiber‐resin and consequently, improving the reinforcement efficiency. POLYM. COMPOS., 39:E2116–E2124, 2018. © 2017 Society of Plastics Engineers

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