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In the context of ion transfer batteries, highly oriented pyrolytic graphite (HOPG) was studied as a model in aqueous electrolytes to elucidate the mechanism of electrochemical intercalation into graphite. The local and time-dependent dimensional changes of the host material occurring during the electrochemical intercalation processes were investigated on the nanometer scale. Atomic force microscopy (AFM), combined with cyclic voltammetry, was used as an in situ analytical tool during the intercalation of perchlorate and hydrogen sulfate ions into and their expulsion from the HOPG electrodes. For the first time, a reproducible, quantitative estimate of the interlayer spacing in HOPG with intercalated perchlorate and hydrogen sulfate ions could be obtained by in situ AFM measurements. The experimental values are in agreement with theoretical expectations, only for relatively low stacks of graphene layers. After formation of stage IV, HOPG expansion upon intercalation typically amounts to 32% when tens of layers are involved but to only 14% when thousands of layers are involved. Blister formation and more dramatic changes in morphology were observed, depending on the kind of electrolyte used, at higher levels of anion intercalation.

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Glassy carbon (GC) is a well known material frequently used in analytical electrochemistry. Numerous investigations of the catalytic surface properties of activated GC have been reported. 1 The GC electrodes can be activated along different routes such as wet chemical, dry chemical, or electrochemical oxidation. Laser activation has also been suggested by Pontikos and McCreery. 2 The numerous possibilities for carbon surface activation have been described in articles and book by McCreery 3 and by Kinoshita. 4 In electrochemical activation, a number of choices exist as to how to modify the surface, such as galvanostatic, potentiostatic, or cyclic polarization in various electrolytes. Film growth by cycling and the corresponding optical properties of the active layer were investigated earlier in our laboratory using spectroscopic ellipsometry. 5 Electrochemical double-layer capacitors (EDLC), also called supercaps or ultracaps, utilize high-surface area electrodes in order to achieve a high-double-layer capacitance. Three main categories of electrode materials typically are used in these EDLCs, viz., carbons, polymers, and metal oxides. 6 For noble metal oxides such as RuO 2 specific capacitance of more than 700 F/g was reported, 7 but these materials are generally considered as being too costly. Redox active polymer films are also considered to be potential electrode materials for EDLCs, 8 but most of them are rather slow, and their long-term stability and cycle life are still uncertain. High-surface area carbons are relatively inexpensive EDLC electrode materials with a relatively high specific capacitance of up to 100 F/g. 9 Therefore, in most of the capacitors available today, carbon materials are used for the electrodes. Problems still arise from the contact resistance between carbon powder particles and from that between the active layer and the current collector sheet. Metal particles or fibers have been added to the carbon powder in order to overcome the grain-to-grain resistance. 10 The use of GC for electrochemical EDLCs was suggested about 20 years ago in a patent by Miklos et al. 11 Activation of the GC surface was attained by gas-phase oxidation at elevated temperatures. Electrochemical activation was not considered in that patent.Several advantages are expected from modified glassy carbon when this is used as an electrode material in EDLCs. It is a reasonably good electronic conductor (200 S/cm) 1,12 and can therefore also be used as the current collector. In addition, GC is impermeable to gases and ions, so that a bipolar plate/electrode assembly (BPEA) can be created by simply modifying a glassy carbon sheet on both sides. 13 However, when working with GC one has to be aware of the fact that depending on the precursor material and temperature used during the pyrolysis process, rather different kinds of GC exist. 1 Properties such as the conductivity, density, reactivity, number, and diameter of internal closed pores, etc. are determined by the pyrolysis temperature. GC is still considered an expen...

In view of large-scale applications, electrochemical exfoliation of graphite for the production of graphene sheets must follow chemical processes that ensure high quality of the products -wide-size graphene foils, single- or few-layer thickness, and low level of defectivity -in order to guarantee high electrical transport and good mechanical properties. Understanding the exfoliation process of graphite at the atomic scale, that is, the intercalation of graphene layers in the electrolyte solution, is fundamental to really be able to control and optimize such processes. This can be obtained, for instance, by investigation of the exfoliated graphite -the surface of the original crystal left behind in the chemical solution- and by real-time monitoring of graphite surface morphological and structural modifications during the exfoliation process. Here, we monitor graphite surface changes as a function of the electrochemical potential by both electrochemical (EC) atomic force microscopy and EC scanning tunneling microscopy coupled with cyclic voltammetry. Following this strategy, we disclose the surface modifications encountered during the early stages of anion intercalation, for different electrolytes: surface faceting, step erosion, terrace damages, and nanoprotrusions, all affecting the graphite surface and therefore the exfoliation process. Our results represent a key step toward a full investigation of the intercalation process in graphite. Within the current debate on the exfoliation of layered crystals, these data potentially represent important information for investigation of the intercalation process in graphite and, on the other hand, for further optimization of the electrochemical protocol for graphene production