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Title: Atypical Hydrogen Uptake on Chemically Activated, Ultramicroporous Carbon

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.
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. ORNL
Publication Date:
OSTI Identifier:
979242
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Carbon; Journal Volume: 48; Journal Issue: 5
Research Org:
Oak Ridge National Laboratory (ORNL); High Temperature Materials Laboratory
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ACTIVATED CARBON; ADSORBENTS; ADSORPTION; ADSORPTION HEAT; ALKALI METALS; CAPACITY; CARBON; CHEMICAL ACTIVATION; DESORPTION; HYDROGEN; HYDROGEN STORAGE; HYPOTHESIS; HYSTERESIS; ISOTHERMS; KINETICS; SURFACE AREA