Carbide-derived carbon volumes

To optimize the device volumetric capacitance density, once the DLC geometric parameters such as the cell size, the electrode thickness, and width have been fixed, the development efforts must be concentrated on the research of the carbon performance. Typical commercial carbons [18] have a capacitance density in the range of 50F/cm3. Their capacitance specific density is in the range of 100 F/g. Among the best-performing carbons available, there are those derived from metal carbide (carbide derived carbon [CDC]) [19,20], They may reach a capacitance density of 130-140F/g. At that point, to avoid confusion, it is worth mentioning the difference between carbon or electrode capacitance and DLC capacitance. The later is exactly four times smaller because of the series connection of two electrodes whose volume is half of the total electrode volume. 

Unlike ACs, carbide-derived carbons (CDCs) can be synthesized in such a way that they only exhibit extremely narrowly distributed micropores and no mesopores but, unlike OMCs, pores are not arranged in an ordered fashion. CDCs are most commonly produced by etching of carbide powders in dry chlorine gas at elevated temperatures (200-1200°C), but they can also be derived from monoliths, fibers, or thin films. The chlorine treatment followed by subsequent hydrogen annealing to remove residual chlorine compounds yields an SSA of typically between 1200 and 2000 va lg but activation may increase the SSA to values of up to 3200 m /g (cf Ref. 87 for a review). Recently, the CDI capacity of CDCs derived from titanium carbide (i.e., TiC-CDC) has been investigated, and a positive relation between capacity and the volume of pores smaller than 1 nm was suggested. This study suggests that the pore volume associated with ion accessible micropores is particularly attractive for CDI, and not, as it may be implied from the studies on OMC, the volume of mesopores. 

FIGURE 3.3 Calculated pore volumes for CDC from various metal carbides assuming conformal transformation. (From Dash, R.K., Nanoporous carbons derived from binary carbides and their optimization for hydrogen storage, PhD Thesis, Drexel University, Philadelphia, PA, 2006.)... 

Carbon fibers, as well as ceramic oxide and carbide fibers, which have a combined sales volume well below that of glass fibers, are derived from solid precursor or green fibers. These precursor fibers are in turn derived from a liquid phase, e.g., from a viscous solution or from a viscous polymer by dry or melt spinning, respectively. By virtue of its organization, this book is uniquely able to pay equal attention to the formation, structures and properties of the... 

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