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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 ∼1.5 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.

High surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200–1200 °C. Structural analysis showed that this carbide-derived carbon (CDC) was highly disordered at all synthesis temperatures. Higher temperature resulted in increasing ordering and formation of bent graphene sheets or thin graphitic ribbons. Soft X-ray absorption near-edge structure spectroscopy demonstrated that CDC consisted mostly of sp 2 bonded carbon. Small-angle X-ray scattering and argon sorption measurements showed that the uniform carbon-carbon distance in cubic TiC resulted in the formation of small pores with a narrow size distribution at low synthesis temperatures; synthesis temperatures above 800 °C resulted in larger pores. CDC produced at 600–800 °C show great potential for energy-related applications. Hydrogen sorption experiments at −195.8 °C and atmospheric pressure showed a maximum gravimetric capacity of ∼330 cm 3 /g (3.0 wt.%). Methane sorption at 25 °C demonstrated a maximum capacity above 46 cm 3 /g (45 vol/vol or 3.1 wt.%) at atmospheric pressure. When tested as electrodes for supercapacitors with an organic electrolyte, the hydrogen-treated CDC showed specific capacitance up to 130 F/g with no degradation after 10 000 cycles.

Porous carbons have received much attention recently for potential applications in energy generation and storage, molecular sieving, and environmental remediation. Property optimization for specific applications rests largely on controlling the volume, size, and shape of the pores at the synthetic level. Direct atom-scale experiments which might accurately and reliably measure these quantities are problematic, so indirect methods such as gas sorption are generally employed. Here we apply a second indirect method, small-angle X-ray scattering (SAXS), to study porosity in carbide-derived carbons (CDC). The results qualitatively confirm and reinforce model-dependent conclusions drawn from gas sorption isotherms. In particular, both techniques indicate the onset of broad polydispersity under the same processing conditions for particular porous carbon materials.

( R )-3- t -butyldimethylsilyloxy-5-acetoxy-1-pentanol has been obtained by PFL catalyzed hydrolysis of the corresponding diacetate and has been utilized for the formal synthesis of the most widespread heterocyst glycolipid of N 2 -fixing cyanobacteria.

( R )-3- t -butyldimethylsilyloxy-5-acetoxy-1-pentanol has been obtained by PFL catalyzed hydrolysis of the corresponding diacetate and has been utilized for the formal synthesis of the most widespread heterocyst glycolipid of N 2 -fixing cyanobacteria.

The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.