Small Angle X-Ray Scattering from Nanoporous Biocarbon

1

• Small Angle X-Ray Scattering from Nanoporous
  Biocarbon
• Mikael Wood1, Jacob Burress1, Peter Pfeifer1, Jan
  Ilavsky2
• Department of Physics and Astronomy, University
  of Missouri-Columbia, 223 Physics Building UMC,
  Columbia MO 65211
• X-ray Operations Division, Argonne National
  Laboratory, Argonne, IL 60439

Project Overview
Hydrogen Uptake
Small Angle X-Ray Scattering

• As a member of the Alliance for Collaborative
  Research in Alternative Fuel Technology
  (ALL-CRAFT) our research group studies the
  properties of powdered and monolithic nanoporous
  biocarbon produced from waste corn cob, with the
  goal of achieving the 2010 DOE gravimetric and
  volumetric targets for vehicular hydrogen (H2)
  and methane (CH4) storage.

77K, 47 bar 300K, 47 bar
S-33/k Hiden 7.9 mass 1.2 mass
S-33/k Pfeifer 7.3 9.1 mass 1.0 -1.2 mass
S-33/k Parilla 8 mass 1.4 1.6 mass
AX-21 () 5.1 mass .6 mass
MOF-177 () 10 mass 2.4 mass
SAXS curve for sample S-33/k
107
106
Dsurface 2.3
105
104
Scattered Intensity 1/cm
() - E. Poirier, et al, Storage of hydrogen on
single-walled carbon nanotubes and other carbon
structures. Appl. Phys. A 78, 961-967
(2004). () (a) O.M. Yaghi, Hydrogen storage
in metal-organic frameworks. 2006 DOE Hydrogen
Program Review, ST22. (b) NSF News Release
06-043 (3/9/06) New crystal sponge triples
hydrogen storage.
103
Fig 1 SEM image of sample S-33/k
102

• The values in the table reflect amount stored
  (both adsorbed and non-adsorbed gas).
• This is a directly measurable quantity,
  requiring no information about nanopore volume
  and density of the adsorbed phase, and is the
  quantity of foremost interest for vehicular
  storage.
• As can be seen our storage values have been
  independently verified and compare well with the
  best performing carbons in the literature.

2p/L

• Pore structure of carbon analyzed via Small
  Angle X-ray Scattering (SAXS), nitrogen and
  methane adsorption, and Scanning Electron
  Microscopy (SEM).
• ALL-CRAFT is based on the 2002 discovery by
  Pfeifer et al. of carbons crisscrossed by a
  nearly space-filling network of channels 1.5 nm
  wide.

101
10-2.5
10-2
10-1.5
10-1
10-.5
Scattered Wave Vector 1/Å
Fig 5 SAXS curve for sample S-33/k with fitted
single cylinder scattering curve

• The behavior of the experimental scattering
  curve for some of our samples show a q-1 behavior
  at high q. These curves also have a large plateau
  at high q. Our hypothesis is that these samples
  contain a correlated network of cylindrical
  pores.
• By fitting the scattering of a single cylinder
  of finite thickness to the experimental
  scattering data via a least squares method in the
  length and radius variables we are able to
  determine the most prominent pore size in our
  sample.
• For the sample S-33/k, shown above, we determine
  a radius of 2.5Å and a length of 14Å. These
  values are in good agreement with pore size data
  from both nitrogen and methane adsorption.

Methane Uptake
Fig 2 STEM image from early carbon sample.
Adsorption Data
ALL-CRAFT Best Performance S-33/k ANG DOE Target
M/M 230-239 g/kg N/A
M/V 115-119 g/L 118 g/L
V/V 176-182 L/L 180 L/L

• BET surface area from nitrogen isotherm 2200
  m2/g for S33/k surface area of latest samples
  3000-3500 m2/g
• Total pore volume 1.09 ml/g
• Pore Size Distribution (PSD) from nitrogen shows
  majority of pore volume is contributed by pores
  with width lt 20 Å.
• Micropore volume .96 ml/g, 88 of total pore
  volume
• PSD peaked at 5.5Å and 11Å

Peak at 5.5Å
Peak at 11Å

• Methane uptake measured gravimetrically on
  powder samples, monoliths measured volumetrically
  as well.
• Values below reported as amount of methane
  stored using a powder density of 0.5 g/ml

Acknowledgements
Fig 3 PSD from nitrogen.

• PSD obtained from methane adsorption agrees well
  with nitrogen data.
• Majority of pores have width lt 20Å
• Yields total pore volume of 1.9 ml/g

This research is based on work supported by the
National Science Foundation, under Grant No.
EEC-0438469, the University of Missouri, the
Department of Education (GAANN), and the Midwest
Research Institute. Use of the Advanced Photon
Source was supported by the U.S. Department of
Energy, under Contract No. W-31-109-Eng-38. And
a very special thanks to Dr. Jan Ilavsky for all
of his wonderful help and insight.

• Many methods exist for determining PSDs (N2,
  CH4, Hg, etc.)
• Small Angle X-Ray Scattering (SAXS) is one of
  the few methods that allows us to see how the
  pores are arranged spatially.
• SAXS provides spatial information over four
  decades of length (5Å 50,000 Å)

Fig 4 PSD from methane.