We have explored the adsorption kinetics of argon and methane on chemically opened and on as-produced carbon nanotubes. We monitored the evolution of the adsorbate pressure after each gas dose was added to the cell during the performance of adsorption isotherms. We found significant differences between the equilibration times measured on these two groups of nanotubes. We propose an explanation for our experimental observations that makes use of recent computer simulations conducted for similar adsorbed systems.
We report on the performance of supercapacitor devices
fabricated
using 1-pyrenecarboxylic acid (PCA)-functionalized graphene electrodes.
The specific capacitances obtained (using 6 M KOH aqueous solution
as an electrolyte) was found to be an order of magnitude higher than
nonfunctionalized graphene electrodes (∼30 and ∼200
F/g for pure graphene and PCA-functionalized graphene electrodes,
respectively). The analysis of electrochemical impedance spectroscopy
using equivalent circuit modeling as well as electrolyte wettability
measurements shows a substantial increase in the electrical double
layer capacitance due to the PCA functionalization. These findings
indicate that PCA functionalization of graphene can significantly
enhance the capacitive storage ability of graphene-based electrodes
and can act as superb electrode materials in electrical energy applications.
We have measured adsorption of xenon on purified HiPco single-walled carbon nanotubes (SWNTs) for coverages in the first layer. We compare the results on this substrate to those our group obtained in earlier measurements on lower purity arc-discharge produced nanotubes. To obtain an estimate for the binding energy of Xe, we measured five low-coverage isotherms for temperatures between 220 and 260 K. We determined a value of 256 meV for the binding energy; this value is 9% lower than the value we found for arc discharge nanotubes and is 1.59 times the value found for this quantity on planar graphite. We have measured five full monolayer isotherms between 150 and 175 K. We have used these data to obtain the coverage dependence of the isosteric heat. The experimental values obtained are compared with previously published computer simulation results for this quantity.
We report kinetics measurements for the adsorption of methane, ethane, propane, butane, and pentane on close-ended single-walled carbon nanotube bundles. The measurements were conducted by monitoring the adsorption equilibration times. For methane and ethane, equilibration times were found to decrease as the fractional coverage on the surface of the nanotube bundles increased, approaching monolayer completion. However, for propane, butane, and pentane, the opposite trend was observed: for these longer alkanes, there was an increase in the equilibration time with increasing fractional coverage. We propose a plausible explanation for our experimental findings, and we suggest that different mechanisms for attaining equilibrium may be in place for short and long alkane chains.
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