We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a ‘hands-on’ approach, providing practical details and procedures as derived from literature as well as from the authors’ experience, in order to enable the reader to reproduce the results. Section is devoted to ‘bottom up’ approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section covers ‘top down’ techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers’ and modified Hummers’ methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by ...

High-pressure assisted hydrothermal treatment is a green and efficient method for the reduction of graphene oxide. The use of high hydrogen pressure favoured a higher deoxygenation degree and a better restoration of the sp2 conjugation.

A simple, sustainable and affordable approach for the synthesis of highly porous carbons is presented. The procedure is based on the use of sodium thiosulfate as an activating agent and a variety of biomass-based products (glucose, sucrose and gelatine) as carbon precursors. The synthesis scheme involves three steps: a) mixing the reactants by grinding, b) heat treatment at temperatures in the 800-900 ºC range and c) extracting the carbon material from the carbonised solid by simple washing with water. The generation of the pore structure is based on the redox reaction between the carbonaceous matter and sodium thiosulfate acting as an oxidant. In this way, porous carbons with high BET surface areas in the ~ 2000-2700 m 2 g -1 range and large pore volumes of up to 2.4 cm 3 g -1 are obtained. The porosity of these carbons consists of two pore systems made up of narrow micropores of 0.8 nm and larger pores of up to 5 nm. These porous carbons have a certain amount of sulfur ( 2-3 %) that is incorporated into the carbon framework as thiophene-like and oxidised sulfur groups. Additionally, in the case of gelatine, N content up to 2-3 % is preserved.

High-surface area carbons are produced from biomass-based products (wood sawdust and tannic acid) by means of an environmentally friendly process based on the use of sodium thiosulfate as activating agent and an inert salt (KCl) that serves as a confinement medium for the activation reaction. These porous carbons have high BET surface areas of up to 2650 m 2 g-1 , large pore volumes of up to 2.3 cm 3 g-1 and a porosity that combines micro-and mesopores in different amounts depending on the quantity of activating agent employed. Such carbons have two additional remarkable properties: a) they are S-doped (2-6 wt% S) and b) they have good electrical conductivities in the 2.5-4.5 S cm-1 range. The above properties make these carbon materials highly attractive as supercapacitor electrodes. Indeed, when tested in a variety of electrolytes (H 2 SO 4 , TEABF 4 /AN and EMImTFSI) using commercial-level mass loadings, they show high specific capacitances (up to 200 F g-1 , 140 F g-1 and 160 F g-1 in aqueous, organic and ionic liquid electrolytes, respectively) and high capacitance retention at high rates in all the electrolytes in combination with a good stability under cycling and floating modes.

No abstract

A simple one-pot route for the synthesis of highly porous N-doped carbons with an excellent performance as supercapacitor electrodes is presented. The synthesis scheme is based on the carbonization of an organic salt, potassium citrate, at a temperature in the 700-900 ºC range, in the presence of urea. Such porous carbons combine ultra-high BET surface areas of up to 3350 m 2 •g-1 , a large pore volume of up to 2.65 cm 3 •g-1 , a porosity which can be regulated to have a micropore or micro-mesopore network and a notable nitrogen content in the 0.5-4.5 wt % range, two essential properties for their use in electrochemical devices. The presence of urea in the synthesis mixture is the key to pore development in these synthesized carbons. The applicability of this type of carbon as supercapacitor electrode material with an ionic liquid as electrolyte has also been demonstrated in this study.

No abstract

No abstract