Zeolite-Templated Carbon Materials for High-Pressure Hydrogen Storage

Abstract

IntroductionAdditional materials characterization and data analysis were performed to supplement the results reported in "Zeolite-Templated Carbon Materials for High Pressure Hydrogen Storage" to assure reproducibility of the results, validate the templated structure of ZTCs, further analyze the micropore character of MSC-30 and ZTCs, and to probe differences in chemical bonding between MSC-30 and ZTCs that could clarify their significant difference in skeletal density.The correlation between BET surface area and excess hydrogen uptake across all temperatures and pressures in ZTCs and the other materials studied is central to the conclusions from this study. In addition to standard hydrogen adsorption/desorption measurements, we also include hydrogen cycling results to show full reversibility of hydrogen uptake and to verify that the experimental error in measurements is acceptable. Secondly, the BET method for characterizing the surface area of materials was supplemented by the Dubinin-Radushkevich method for determining microporous volume to determine the correlation between this value and excess hydrogen uptake at room temperature.Additional comparison of material properties of ZTC-3 and other ZTCs is important for validating the comparison of our high pressure results to those in the literature. Electron microscopy, both scanning (SEM) and transmission (TEM), was performed to show the similarity of ZTC-3 to "PFA-P7-H" synthesized by Ma et al. 38 , an approximately equivalent reference material to "P7(2)-H" of Nishihara et al. 16 Finally, some measurements were performed to determine if there were differences in sp 2 or sp 3 chemical bonding in ZTC-3 and MSC-30, including x-ray photolelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS), and solid-state 13 C nuclear magnetic resonance (NMR). The motivation for this additional work was elucidation of the nature of the different skeletal density between the two materials. However, no significant differences were detected that could account for the large difference in skeletal density. The results are consistent with those in the literature, for example by Yang et al. 33(XPS results) and Ma et al. 32 (NMR results). Hydrogen CyclingHydrogen uptake isotherms measured up to 30 MPa, using our newly constructed Sieverts apparatus specific to high pressure experiments, were cycled multiple times to ensure repeatability of the results. Hydrogen cycling in all materials studied was achieved without any loss of capacity on adsorption and desorption after many cycles, as expected for pure physisorbent materials. For example, three consecutive hydrogen adsorption/desorption cycles in ZTC-3 at 298 K are shown in Figure S1. The sample was degassed before cycling, as detailed in the Experimental Methods, but was not degassed in between cycles. Dubinin-Radushkevich Micropore VolumeNitrogen adsorption isotherms at 77 K were further analyzed to determine the Dubinin-Radushkevich (DR) micropore volume 21 of each sample. The DR method for treating the N 2 ...

Anomalous Isosteric Enthalpy of Adsorption of Methane on Zeolite-Templated Carbon

“…4 In summary, it was found that ZTC-3 has chemical properties similar to other ZTCs (being predominantly sp 2 hybridized carbon) and has very high template fidelity, having the structural traits of the best reported examples. 5,6 Its hydrogen adsorption properties are among the highest of reported carbonaceous materials, but are proportional to surface area between 77-298 K as for other carbons.…”

“…BET surface areas are reported, as previously discussed. 4 The excess methane capacities measured at 247, 298, and ~523 K from Figure 2 are tabulated for comparison. The skeletal density of ZTC-3, consistent with other ZTCs, is lower than the typical value expected for carbonaceous materials: 1.8 g mL -1 , 81% of the skeletal density of pure graphite.…”

“…The pore-size distribution (left) and relative filling (right) of CNS-201 (black), MSC-30 (red), ZTC "P7(2)-H" (blue), and ZTC-3 (purple), calculated by the NLDFT method. 4,5,9,10 It has been proposed that 1.14 nm is the optimal spacing between graphene layers for maximum adsorption uptake of methane. 11,12 The pore-size distribution of ZTC-3 has a mean pore-width close to this value, shown as a gray line in Figure S1.…”

“…A PID controller and K-type thermocouples were used to maintain a consistent temperature throughout measurement; fluctuations were less than ±0.1 K at low temperature and no higher than ±0.4 K at high temperatures. The system was leak tested up to 10 MPa and showed a maximum leak rate of 7.0 × 10 -6 mol h -1 of CH 4 . If fitted to an exponential decay function, n(t) = n 0 exp (-kt) where k is the leak rate, this corresponds to a maximum leak of k ~ 10 -8 s -1 which is negligible for short time measurement.…”

Large surface area sucrose-based carbons via template-assisted routes: Preparation, microstructure, and hydrogen adsorption properties

“…The past decade in particular has witnessed a rapidly growth in diverse applications, especially in the hydrogen storage [11][12][13][14][15][16][17]. In order to meet the requirements of hydrogen storage, a more refined control on the microporosities, surface chemistry and morphology of carbons is very desired [18].…”