Hydrogen storage in nanoporous carbons

International Journal of Hydrogen Energy, 2009

Chemical and physical activation Pore size a b s t r a c t Development of high-capacity hydrogen-storage systems utilizing physisorption at high pressure and low temperature is hindered by poor understanding of the pore size/shape requirements for achieving the maximum hydrogen uptake. Tuning the carbon structure and pore size of carbide-derived carbons (CDCs) with high accuracy by using different starting carbides, chlorination temperatures and activation temperatures allows rational design of carbon materials with increased hydrogen-storage capacity. Systematic experimental investigation of a large number of CDCs with controlled pore size distributions and specific surface area (SSA) shows that pores larger than w1.5 nm contribute little to hydrogen storage. It has been experimentally demonstrated that, just as at ambient pressure, pores of 0.6-0.7 nm in diameter provide the largest H 2 uptake per unit SSA at elevated pressures and liquid nitrogen temperatures. The effect of pore size was stronger than the effect of surface chemistry on the hydrogen uptake. ª A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

Applied Surface Science, 2012

The hydrogen adsorption capacity of different types of carbon nanofibers (platelet, fishbone and ribbon) and amorphous carbon have been measured as a function of pressure and temperature. The results showed that the more graphitic carbon materials adsorbed less hydrogen than more amorphous materials. After a chemical activation process, the hydrogen storage capacities of the carbon materials increased markedly in comparison with the non-activated ones.

2010

• Develop and demonstrate reversible hydrogen storage in carbide-derived carbons (CDC) with tunable nanoporosity. • Determine the optimum pore size for hydrogen storage using experiment and theory. • Design a CDC-based hydrogen storage material that meets 2010 DOE performance targets and commercialize it.

Carbon, 2019

Hydrogen adsorption in highly porous carbon with well-defined pores, with three different shapes, and different sizes ranging from sub-to nanometers is investigated. Using a combined approach of volumetric gas adsorption method and in-situ quasi-elastic neutron scattering method the relationship between final macroscopic intake properties, details of the local adsorbent structure and the molecular behaviour of confined hydrogen are established. It is shown that sub-nanometer pores of spherical and cylindrical shape strongly limit the diffusion of H 2 , and thus, enhance the H 2 storage capability of carbons with welltailored pore structure. In mesoporous carbide-derived carbon, the formation of a hydrogen layer with reduced mobility close to the pore walls is observed. With the increase in the amount of confined hydrogen and the occupation of the centre pore area, the mobility of confined hydrogen increases in a jumpelike fashion. Surprisingly, the increase of hydrogen diffusion is also observed at higher hydrogen loadings, indicating that cooperative H 2 eH 2 interactions might play a role.

2005

METHODS Materials. The experimental setup and structure/composition of carbide powders for synthesis of CDC have been described elsewhere. 1 While many CDCs have been studied, providing a large volume of statistically reliable data, only data for CDC produced from boron carbide (B 4 C), titanium carbide (TiC), zirconium carbide (ZrC) and silicon carbide (β-SiC) are referred to in this work. The particle sizes of the powders were 6 µm, 2 µm, 8 µm and 0.7 µm, respectively. The synthesis of CDC from these carbides was described in our previous publications. 1, 2 The starting material was placed into the quartz tube of a resistance furnace in a quartz boat. The furnace was then heated to the desired temperature (400-1200 o C) under argon (BOC Gases, 99.998%) purge. Once the desired reaction temperature was reached, chlorine gas (BOC Gases, 99.5%) at 10-15 cm 3 /min was passed through the tube furnace for 3 hours. After chlorination, the furnace was cooled to room temperature under argon purge. Hydrogen annealing was done using the same furnace at 600°C for 2 h. As shown by PGAA, chlorine trapped during the synthesis was a major contamination in the sample but its content decreases well below 1 at% after hydrogen treatment. Carbide forming metals may eventually be present in incompletely chlorinated samples, but their content in the TiC-CDC samples used to generate data of Fig. 3 was ~0.05 at.%. Several other materials have been studied for comparison and independent verification of the results for CDC reported here. These include SWCNT from Rice University (TUBES@RICE) and open ended nanotubes from NanoCarbLab, Moscow (http://www.nanocarblab.com). According to the manufacturer, the latter sample was purified and activated by combination of acid treatment (HCl and HNO 3) and thermal oxidation in air flow. At the end, nanotubes were washed in water and dried in air flow at 140°C. Neutron powder diffraction performed at NIST indicated some graphite and nickel in that sample. Both of these SWNT materials stored less hydrogen than arc-discharge produced nanotubes oxidized at 350°C and containing metal oxide 3 , so we report the latter in Fig. 3b as the best reliable result for SWCNT available to us. The MWCNT (10-20 nm diameter) reported in Fig. 3b come from Arkema, France, and were produced by a catalytic CVD technique. Deuturated MOF-5 samples with the molecular formula Zn 4 O 13 C 24 D 12 were produced at NIST. Their structure and composition were confirmed by neutron scattering. The result that we obtained (Fig. 3a, 1.25 wt.% of H 2) is in good agreement with 1.3 wt.% reported for MOF-5 by Yaghi's group. 4 Sorption analysis. Quantachrome Autosorb-1 was used for sorption analysis with argon as adsorbate at 77K as reported previously. 2 The SSA of the carbon material was calculated according to BET (Brunauer, Emmet, Teller) equation 5 and pore volume was calculated from argon adsorption using nonlocal density functional theory (NLDFT). 29 Weighted pore size of the carbons was defined as References:

Carbon, 2021

Our investigations into molecular hydrogen (H 2) confined in microporous carbons with different pore geometries at 77 K have provided detailed information on effects of pore shape on densification of confined H 2 at pressures up to 15 MPa. We selected three materials: a disordered, phenolic resin-based activated carbon, a graphitic carbon with slit-shaped pores (titanium carbide-derived carbon), and single-walled carbon nanotubes, all with comparable pore sizes of <1 nm. We show via a combination of in situ inelastic neutron scattering studies, high-pressure H 2 adsorption measurements, and molecular modelling that both slit-shaped and cylindrical pores with a diameter of~0.7 nm lead to significant H 2 densification compared to bulk hydrogen under the same conditions, with only subtle differences in hydrogen packing (and hence density) due to geometric constraints. While pore geometry may play some part in influencing the diffusion kinetics and packing arrangement of hydrogen molecules in pores, pore size remains the critical factor determining hydrogen storage capacities. This confirmation of the effects of pore geometry and pore size on the confinement of molecules is essential in understanding and guiding the development and scale-up of porous adsorbents that are tailored for maximising H 2 storage capacities, in particular for sustainable energy applications.

Journal of Non-Crystalline Solids, 2006

Porous carbon is considered a promising material to store hydrogen. It can be visualized as a defective relaxed sample and therefore some of the methods we have developed to deal with porous silicon are presently applied to this material. Porous atomic structures with 50% porosity that, due to the size of the supercells fall within the regime of nanoporous carbon, are generated using our procedure. Two pure nanoporous samples of densities 1.75 g/cm 3 and 1.31 g/cm 3 were hydrogenated, relaxed and their total energy obtained. The hydrogenated samples were first stripped of the hydrogen atoms and their total energy obtained. Then the original samples were stripped of the carbon atoms and the total energy calculated. From these values the average energy per hydrogen atom was then deduced. We compare our results to CH bond energies; conclusions are drawn.

Nanotechnology, 2009

It is shown how appropriately engineered nanoporous carbons provide materials for reversible hydrogen storage, based on physisorption, with exceptional storage capacities (∼80 g H 2 /kg carbon, ∼50 g H 2 /liter carbon, at 50 bar and 77 K). Nanopores generate high storage capacities (a) by having high surface area to volume ratios, and (b) by hosting deep potential wells through overlapping substrate potentials from opposite pore walls, giving rise to a binding energy nearly twice the binding energy in wide pores. Experimental case studies are presented with surface areas as high as 3100 m 2 g −1 , in which 40% of all surface sites reside in pores of width ∼0.7 nm and binding energy ∼9 kJ mol −1 , and 60% of sites in pores of width >1.0 nm and binding energy ∼5 kJ mol −1 . The findings, including the prevalence of just two distinct binding energies, are in excellent agreement with results from molecular dynamics simulations. It is also shown, from statistical mechanical models, that one can experimentally distinguish between the situation in which molecules do (mobile adsorption) and do not (localized adsorption) move parallel to the surface, how such lateral dynamics affects the hydrogen storage capacity, and how the two situations are controlled by the vibrational frequencies of adsorbed hydrogen molecules parallel and perpendicular to the surface: in the samples presented, adsorption is mobile at 293 K, and localized at 77 K. These findings make a strong case for it being possible to significantly increase hydrogen storage capacities in nanoporous carbons by suitable engineering of the nanopore space.

2009

International Journal of Hydrogen Energy, 2009

Carbon nanomaterials Nanostructured carbon Physisorption Chemisorption a b s t r a c t Recent developments focusing on novel hydrogen storage media have helped to benchmark nanostructured carbon materials as one of the ongoing strategic research areas in science and technology. In particular, certain microporous carbon powders, carbon nanomaterials, and specifically carbon nanotubes stand to deliver unparalleled performance as the next generation of base materials for storing hydrogen. Accordingly, the main goal of this report is to overview the challenges, distinguishing traits, and apparent contradictions of carbon-based hydrogen storage technologies and to emphasize recently developed nanostructured carbon materials that show potential to store hydrogen by physisorption and/or chemisorption mechanisms. Specifically touched upon are newer material preparation methods as well as experimental and theoretical attempts to elucidate, improve or predict hydrogen storage capacities, sorption-desorption kinetics, microscopic uptake mechanisms and temperature-pressure-loading interrelations in nanostructured carbons, particularly microporous powders and carbon nanotubes. ª (Y. Yü rü m).