Atypical Hydrogen Uptake on Chemically Activated, Ultramicroporous Carbon
- ORNL
Hydrogen adsorption at near-ambient temperatures on ultramicroporous carbon (UMC), derived through secondary chemical activation from a wood-based activated carbon was studied using volumetric and gravimetric methods. The results showed that physisorption is accompanied by a process of different nature that causes slow uptake at high pressures and hysteresis on desorption. In combination, this results in unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt % at 25 oC and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17 20 kJ/mol) is higher than usually reported for carbon materials, but the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption caused by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Temperature Materials Lab. (HTML)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 979242
- Journal Information:
- Carbon, Vol. 48, Issue 5; ISSN 0008-6223
- Country of Publication:
- United States
- Language:
- English
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