Small Angle X-Ray Scattering from Nanoporous BiocarbonSmall Angle X-Ray Scattering from Nanoporous BiocarbonMikael Wood1, Jacob Burress1, Peter Pfeifer1, Jan Ilavsky2

1) Department of Physics and Astronomy, University of Missouri-Columbia, 223 Physics Building UMC, Columbia MO 65211

2) X-ray Operations Division, Argonne National Laboratory, Argonne, IL 60439

cc

cccc

200 nm

5.00 μm

Project OverviewProject Overview• 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.

• 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.

Peak at ~11Å

Adsorption DataAdsorption Data

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0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

Pore Width Range [nm]

Po

re V

olu

me

[m

L/g

]

• 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 < 20 Å.• Micropore volume = .96 ml/g, 88% of total pore volume•PSD peaked at ~5.5Å and ~11Å

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

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%

Hydrogen UptakeHydrogen Uptake

(*) - 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.”

• 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.

101

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10-2.5 10-2 10-1.5 10-1 10-.5

Dsurface~ 2.3

1I q

q

~2π/L

2 2o r L

2r

L

SAXS curve for sample S-33/k

Sca

tter

ed I

nte

nsi

ty [

1/cm

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Scattered Wave Vector [1/Å]

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

Small Angle X-Ray ScatteringSmall Angle X-Ray Scattering

Peak at ~5.5Å

• 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

Methane UptakeMethane Uptake• 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.

Fig 6: Two pore structures that yield similar PSDs, but have vastly different SAXS curves

• 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 1: SEM image of sample S-33/k

Fig 2: STEM image from early carbon sample.

Fig 3: PSD from nitrogen.

Fig 4: PSD from methane.

Fig 5: SAXS curve for sample S-33/k with fitted single cylinder scattering curve

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.

AcknowledgementsAcknowledgements