| NMG members
working on CDC include: G. Yushin (group leader), J. Chmiola
(electrochemical applications), R. K. Dash (H2, CH4, CO2,
and Cl2 gas storage), Z. Cambaz (CDC transformations at the
nano-scale), E. Hoffman (gas/liquid separation and
purification), D. Vriehof (gas storage), S. Yachamaneni
(bio-applications). |
|
CDC is produced by extraction
of metals from metal carbides. The method permits synthesis
of almost all known carbon structures including amorphous
and nanocrystalline graphitic carbon, graphite ribbons,
carbon nanotubes, carbon onions, nanodiamond, and ordered
graphite. In addition, CDC synthesis allows formation of
highly porous carbon materials with good mechanical
properties. Microstructure, pore size, pore shape, and
surface termination of nanoporous CDC can be precisely
controlled by changing the process parameters and the
composition and structure of the initial carbide precursor.
As such, the process allows optimization of nanoporous CDC
for various applications. |
 |
Tuning the carbon
structure and pore size with high accuracy by using
different starting carbides and chlorination temperatures
allows rational design of carbon materials with enhanced
performance for the variety of applications. |
|
Tuning the Pore Size in
Ti3SiC2 - CDC with Sub-A Precision (Y. Gogotsi et al.
Nature Materials, 2003 (2) 591-594) |
|
 |
| High Resolution TEM images of
various forms of carbon produced during chlorination of
carbides: amorphous carbon (a), turbostratic graphite (b),
fullerene-like carbon (c), nanodiamond (d), carbon onion
(e), graphite ribbons (f), carbon nanotubes (g), barrel-like
particles (h), and ordered graphite (i). (G. Yushin et
al., in Handbook of Nanomaterials ed. by Y. Gogotsi, 2005,
CRC Press, 237-280) |
|
Selected Applications |
| I. Supercapacitors
(Electrical Double Layer Capacitors - EDLC) |
|
Supercapacitors are
electrochemical energy storage devices akin to batteries.
Occupying a region between batteries and dielectric
capacitors on the Ragone plot, a plot describing the
relationship between energy and power, they have been touted
as a solution to the mismatch between the fast growth in
power required by devices and the inability of batteries to
efficiently discharge at high rates. This large capacity for
high power discharge is directly related to the absence of
charge transfer resistances that are a consequence of
battery Faradaic reactions. This subsequently leads to low
temperature dependence and theoretically unlimited
cyclibility in supercapacitors. Improvements in the energy
density of supercapacitors may help the currently made
batteries work better and help usher electrical and fuel
cell cars to the road.
Fast growing market of supercapacitors is expected to reach
$ 1 billion by 2009. Applications of supercapacitors
include: mobile electronics, starting conventional engines
and acceleration boost for hybrids, power for electric
vehicles, and backup power supplies to name a few. |
|
CDC outperformed other carbon materials
for EDLC applications offering the highest volumetric and
gravimetric capacitance, and thus the highest energy density
for the produced devices. |
 |
|
Performance of CDC-based electrodes: specific
capacitance in standard organic electrolytes |
|
Performance of CDC-based electrodes in
standard organic electrolytes: equivalent series resistance
of the assembled EDLC cell of standard (1 cm2) size. |
| II. Hydrogen Storage |
|
The success of any future
hydrogen economy depends, in large part, on our ability to
develop inexpensive materials with sufficient
hydrogen-storage capacity. Cryo-adsorption is considered a
promising method of enhancing gravimetric and volumetric H2
storage for the future transportation needs. |
 |
We have demonstrated that nanoporous CDC
with tunable pore size and pore volume up to 1 cc/g
available for hydrogen storage possess gravimetric hydrogen
storage density up to 3.6 wt% at 1 atm pressure and 77K.
Small pores (1 nm or below) are most efficient for hydrogen
sorption while mesopores, detract from volumetric capacity
and contribute little to gravimetric capacity. Large SSA and
total pore volume increase hydrogen uptake for a given pore
size. |
|
Performance of CDC as H2 storage media @ 1 atm, 77K. |
| III. Methane Storage |
| The use of natural gas
(methane) as an automotive fuel offers considerable
advantages, including reduced emission, lower maintenance,
and most importantly lower fuel cost relative to gasoline.
Moreover, the world-wide reserves of natural gas
considerably exceed the oil reserves and thus natural gas
may offer a solution when oil wells run dry. However, in
order to compete with gasoline now (and offer comparable
driving distance for vehicles before re-fueling) advanced
methane storage units with large volumetric and gravimetric
methane storage capacity need to be developed. Storing
natural gas in a compressed form has the disadvantage of the
high cost of high pressure cylinders needed to provide the
adequate methane storage capacity in a reasonably small
volume. The use of inexpensive carbon adsorbent materials
may allow storing considerable amounts of natural gas at
relatively low pressures (<40 bar), making it more
attractive for practical use. |
 |
Similar to hydrogen–storage
applications, CDC can be optimized to adsorb large
quantities of methane. We performed preliminary experiments
on selected CDC samples and discovered that CDC outperforms
commercially available activated carbons offering nearly 30
vol/vol methane storage at room temperature and atmospheric
(≈1 bar) pressure. |
|
Comparison of the highest CH4 storage
capacities achieved in nanostructured carbons at 1 Bar.
The experiments were performed at room temperature. |
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