Characterization of hydrogen storage materials

1
Characterization of hydrogen storage materials

• Oak Ridge National Laboratories
• Hydrogen Storage Workshop
• May 7 8, 2003
• George Thomas, Consultant
• Sandia National Laboratories

2
Development efforts for more efficient hydrogen
storage materials are increasing

• It will become increasingly important to employ
  consistent material characterization methods
• in order to speed the development process
• and make effective use of limited resources
• Inaccurate results take disproportionate amount
  of resources and waste time
• its more difficult to disprove erroneous data
  than it is to generate accurate data
• Development is commercially driven
• timely, consistent and accurate material
  information is needed

3
Development efforts for more efficient hydrogen
storage materials are increasing

• It will become increasingly important to employ
  consistent material characterization methods
• in order to speed the development process
• and make effective use of limited resources
• Inaccurate results take disproportionate amount
  of resources and waste time
• its more difficult to disprove erroneous data
  than it is to generate accurate data
• Development is commercially driven
• timely, consistent and accurate material
  information is needed

4
Development efforts for more efficient hydrogen
storage materials are increasing

• It will become increasingly important to employ
  consistent material characterization methods
• in order to speed the development process
• and make effective use of limited resources
• Inaccurate results take disproportionate amount
  of resources and waste time
• its more difficult to disprove erroneous data
  than it is to generate accurate data
• Development is commercially driven
• timely, consistent and accurate material
  information is needed

5
Development timeline
6
Phases in the development timeline

• Research phase mg gm samples
• achieve reproducibility
• understand mechanisms
• Development phase gm kg samples
• more detailed properties data
• material characterization
• System engineering phase gt kg samples
• operational characterization

7
Research phase

• Three types of analyses
• hydrogen properties measurements
• material characterization
• mechanistic studies
• Correlation of hydrogen properties with
• material synthesis method
• material pretreatment
• material morphology and structure
• material chemistry

8
Hydrogen properties

• hydrogen uptake and hydrogen release
• quantitative measurements
• thermodynamic properties vs. temperature
• kinetic behavior vs temperature
• preferred measurement techniques
• volumetric (for gram samples)
• gravimetric (for milligram samples)
• isothermal for capacity and thermodynamics
• thermal ramp (TPD) for scoping materials
• mass spec. (e.g., RGA) for gas species

9
Material characterization

• material structure
• microscopy
• XRD
• neutron diffraction
• composition
• mechanistic studies
• e.g., NMR, ESR, XPS, AES, Raman, . . .
• neutron scattering
• in-situ experiments

10
Development phase

• Determine material properties which will enable
  the fabrication of larger quantities and the
  design and fabrication of storage systems
• hydrogen properties
• determine pressure-composition-temperature
  relationship (PCT measurements) for uptake and
  release.
• true hydrogen capacity
• H2 release/total weight of material
• (includes dopants, impurities, other dead
  weight)
• kinetic behavior

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Example NaAlH4 doping affects kinetics
(G. Sandrock, K. J. Gross, G. Thomas, JAC 339
(2002) 299)

• Initial kinetics exhibit Arrhenius behavior
• different activiation energy in doped material
• activation energy constant for 2 mol and greater
  doping
• faster kinetics with higher doping levels

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Development phase also provides engineering data
on materials

• Material properties
• particle size, shape
• volume change with absorption/desorption
• packing density
• cycling behavior
• effects of input gas stream impurities on
  capacity, kinetics.
• output gas stream purity
• Other engineering properties
• thermal conductivity of packed bed
• safety issues related to environmental exposure
• e.g., air, water, shock, temperature
• materials compatibility

13
Engineering Properties

• Thermal conductivity
• similar to IM hydrides
• cycling
• stable to 100 cycles
• material compatibility
• no issues with Al, SS
• safety
• autothermal behavior

14
FreedomCAR system targets based on performance
requirements
2005 2010 2015

• specific energy (MJ/kg) 5.4 7.2 TBD weight
  percent hydrogen 4.5 6.0
• energy density (MJ/liter) 4.3 5.4
• system cost (/kg system) 9 6
• operating temperature (C) -20/50
• cycle life 500 1000
• flow rate (g/sec) 3 4
• delivery pressure (bar) 2.5 2.5
• transient response (sec) 0.5 0.5
• refueling rate (kg H2/min) 0.5 1.5
• loss, permeation, leakage, toxicity, safety

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System engineering phasemeasurements on storage
systems

• hydrogen properties
• usable capacity at specified delivery pressure
• steady state delivery flow rate
• fill rate/time
• partial list of system properties
• total weight and volume
• transient response
• cold start temperature and time
• operational temperature range
• coolant/heating requirements
• overall efficiency

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In all development phases, there are many
potential sources of inconsistent results

• small sample sizes (mg)
• lack of consistent pre-treatment of materials
• impurities
• multiple phases present
• sample characterization
• lack of standardized measurement techniques
• gravimetric, volumetric, flow
• hydrogen dosing or loading conditions
• thermal ramp, isothermal
• calibration
• lack of release gas stream analysis (speciation)

17
Example published values for carbon
capacitiesM. Heben, NREL
gt10 wt
lt 1 wt
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This has led to the establishment of an
independent testing facility by DOE

• Southwest Research Institute
• Standardized Testing Program for Emergent
  Chemical Hydride and Carbon Storage Technologies
• Objectives
• Develop and operate a standard testing and
  certification program specifically aimed at
  assessing the performance, safety and life cycle
  of emergent chemical hydride and carbon
  adsorption/desorption hydrogen storage systems.
• Work with industry and the U.S. government to
  develop an accepted set of performance and safety
  evaluation standards.
• Contacts
• R. A. Page
• M. A. Miller

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SwRI standardized testing program

• Project structure not finalized, but the
  following components have been identified
• Intrinsic material properties
• high pressure gravimetric analyzer
• milligram to gram samples
• mass spec. desorption speciation
• Hydride bed systems
• Sieverts apparatus
• gt35 atm operating pressures
• gtkg sample sizes
• Supporting materials characterization

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Summary

• The SwRI independent testing facility should
  contribute to improved reliability and
  consistency of storage material data
• There is also a need for better
• coordination
• collaboration
• information exchange
• between research organizations
• Such interactions could be established through
• working groups
• (example are the alanate and carbon W.G.s)
• virtual centers

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