NMR methods for characterizing the pore structures and hydrogen storage properties of microporous carbons.
Abstract
(1)H NMR spectroscopy is used to investigate a series of microporous activated carbons
derived from a poly(ether ether ketone) (PEEK) precursor with varying amounts of burnoff
(BO). In particular, properties relevant to hydrogen storage are evaluated such as
pore structure, average pore size, uptake, and binding energy. High-pressure NMR with
in situ H(2) loading is employed with H(2) pressure ranging from 100 Pa to 10 MPa.
An N(2)-cooled cryostat allows for NMR isotherm measurements at both room temperature
( approximately 290 K) and 100 K. Two distinct (1)H NMR peaks appear in the spectra
which represent the gaseous H(2) in intergranular pores and the H(2) residing in micropores.
The chemical shift of the micropore peak is observed to evolve with changing pressure,
the magnitude of this effect being correlated to the amount of BO and therefore the
structure. This is attributed to the different pressure dependence of the amount of
adsorbed and non-adsorbed molecules within micropores, which experience significantly
different chemical shifts due to the strong distance dependence of the ring current
effect. In pores with a critical diameter of 1.2 nm or less, no pressure dependence
is observed because they are not wide enough to host non-adsorbed molecules; this
is the case for samples with less than 35% BO. The largest estimated pore size that
can contribute to the micropore peak is estimated to be around 2.4 nm. The total H(2)
uptake associated with pores of this size or smaller is evaluated via a calibration
of the isotherms, with the highest amount being observed at 59% BO. Two binding energies
are present in the micropores, with the lower, more dominant one being on the order
of 5 kJ mol(-1) and the higher one ranging from 7 to 9 kJ mol(-1).
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https://hdl.handle.net/10161/4054Published Version (Please cite this version)
10.1021/ja9109924Publication Info
Anderson, Robert J; McNicholas, Thomas P; Kleinhammes, Alfred; Wang, Anmiao; Liu,
Jie; & Wu, Yue (2010). NMR methods for characterizing the pore structures and hydrogen storage properties
of microporous carbons. J Am Chem Soc, 132(25). pp. 8618-8626. 10.1021/ja9109924. Retrieved from https://hdl.handle.net/10161/4054.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Jie Liu
George Barth Geller Distinguished Professor of Chemistry
Dr. Liu’s research interests are focusing on the chemistry and material science of
nanoscale materials. Specific topics in his current research program include: Self-assembly
of nanostructures; Preparation and chemical functionalization of single
walled carbon nanotubes; Developing carbon nanotube based chemical and biological
sensors; SPM based fabrication and modification of functional nanostructures.

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