Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N 2 ) SSA B1000-3000 m 2 g À1 , and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H 2 O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (o2 nm). A decrease in the activation temperature from 850 1C to 550 1C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by B30%) of the BET (N 2 ) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N 2 ) SSA but for materials with 80-90% of the total pore volume in micropores and an increased BET (H 2 O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte. Fig. 14 Electrochemical analyses of rGO and a-rGO materials activated at 550 1C, 600 1C and 850 1C: (a) CV curves recorded at 50 mV s À1 . (b) Charge/discharge curves recorded at a 1 A g À1 current density. PCCPPaper

High-surface area activated graphene has a threedimensional porous structure that makes it difficult to prepare dispersions. Here we report a general approach that allows the preparatioon of stable water-based dispersions/inks at concentrations of ≲20 mg/mL based on activated graphene using environmentally friendly formulations. Simple drying of the dispersion on the substrate allows the preparation of electrodes that maintain the high specific surface area of the precursor material (∼1700 m 2 /g). The electrodes are flexible because of the structure that consists of micrometer-sized activated graphene grains interconnected by carbon nanotubes (CNTs). The electrodes prepared using activated graphene demonstrate performance superior to that of reduced graphene oxide in supercapacitors with KOH and TEA BF 4 /acetonitrile electrolytes providing specific capacitance values of 180 and 137 F/g, respectively, at a specific current of 1 A/g. The high surface area of activated graphene in combination with the good conductivity of CNTs allows an energy density of 35.6 Wh/kg and a power density of 42.2 kW/kg to be achieved. The activated graphene dispersions were prepared in liter amounts and are compatible with most industrial deposition methods.

A spray gun machine was used to deposit high-surface-area supercapacitor electrodes using green non-toxic aqueous dispersions based on different kinds of high specific surface area nanostructured carbon materials: activated graphene (a-rGO) and activated carbon (AC). Tuning the spray conditions and dispersion formulation allowed us to achieve good adhesion to stainless-steel current collectors in combination with high surface area and a satisfactory mechanical stability of the electrodes. The specific surface area of approximately 2000 m 2 /g was measured directly on a-rGO and AC electrodes showing only around a 20 % decrease compared to the precursor powder materials. The performance of the electrodes deposited on stainless-steel and aluminum current collectors was tested in supercapacitor devices using three electrolytes. The electrodes were tested in an "as-deposited" state and after post-deposition annealing at 200°C. The spray deposition method and post-deposition annealing are completely compatible with roll-to-roll industrial production methods. The a-rGO demonstrated superior performance compared to AC in supercapacitor electrodes with gravimetric capacitance, energy, and power density parameters, which exceed commercially available analogues. The formulation of the dispersions used in this study is environmentally friendly, as it is based on only on water as a solvent and commercially available non-toxic additives (graphene oxide, fumed silica, and carbon nanotubes).

the methods commonly used for the preparation of GO thin films and freestanding foils/membranes.Most of the applications cited above are enabled by the ability of GO multilayers to swell in polar solvents similarly to their precursor graphite oxides. [18][19][20][21][22] In this respect GO is similar to very common clay minerals, e.g., montmorillonites, [23] vermiculites, [24] and bentonites. [25] Swelling occurs in these materials due to sorption of water (or other solvents) between 2D layers and the expansion of interlayered distance. [26][27][28] The driving force of swelling is hydration of anions in clay minerals and hydration of interlayer functional groups in GO. The crystalline swelling refers to layer-by-layer intercalation of solvent. Osmotic swelling is controlled by the relatively easy flow of solvent in and out of structure regulated by osmotic effects. [29][30][31][32][33] Remarkably, crystalline swelling is found for Brodie GO in all so far studied solvents except water [34][35][36][37][38] while for Hummers GO only osmotic-like swelling was so far reported. [37,39,40] Adding water to clays under conditions of confinement is known to produce pressures in the range of tens or even hundreds of bar. [25,41,42] Swelling pressure is complex phenomena, which depends on many parameters, e.g., degree of compaction, [25] concentration of salts in solution, [43] temperature [44] etc. It is an important factor, e.g., in construction works since the pressure is sufficient to induce damage in buildings or roads. Swelling pressure has been studied in detail for clay minerals but so far not reported for multilayered GO and graphite oxides. At the same time, the swelling pressure is an important factor affecting performance of GO membranes.The swelling of GO membranes is directly related to the size of "permeation channels" which enable a flow of solvents and solutions. Strong variation in the size of the "permeation channels" is observed in GO membranes depending on the solvent used, [45] concentration and chemical nature of dissolved molecules or ions, [17] shelf storage time, [40] and many other parameters related to the preparation of membranes. For example, the swelling in liquid ethanol was reported with significant scatter providing d(001) values in the range ≈11-17.7 Å. [10,16,46,47] Swelling in longer alcohols provides interlayer distances up to ≈50 Å. [10,48] There are also examples showing that the swelling of GO membranes can be significantly different compared to precursor graphite oxides. [16,17] Strong variation of interlayer distance in swollen GO membranes is a problem for nanofiltration applications, which require Swelling of graphene oxide (GO) membranes and bulk graphite oxide under confinement conditions is found to produce pressures up to ≈220 bar. Swelling pressure is important to take into account in many applications of GO membranes, but it has not been previously reported. Swelling pressures are typically measured only for bulk materials. However, it is demonstrated that even µm thick GO ...

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High surface area carbons are so far the best materials for industrial manufacturing of supercapacitor electrodes. Here we demonstrate that pine cones, abundant bio-precursor currently considered as a waste in...

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Unlike many chemical modification methods of GO reported in 1930-1960 and re-studied in much details over past decade, acetylation somehow escaped attention and remain almost completely unexplored. Acetylated Graphite Oxide...