# Presentation: 240481

## Characterization of hydrogen storage materials

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

## 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
- it’s 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

## 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
- it’s 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

## 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
- it’s 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

## Development timeline

## 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		> kg samples
- operational characterization

## 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

## 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

## Material characterization

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

## 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

## Example: NaAlH4 doping affects kinetics

***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***

*(G. Sandrock, K. J. Gross, G. Thomas, JAC 339 (2002) 299)*

## 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

## Engineering Properties

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

## FreedomCAR system targets based on performance requirements

- 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

_**2005**_**	**_**2010**_**	**_**2015**_

## System engineering phase:measurements 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

## 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)

## Example: published values for carbon capacitiesM. Heben, NREL

- >10 wt%

- < 1 wt%

## 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

## 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
- >35 atm operating pressures
- >kg sample sizes
- Supporting materials characterization

## 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”

## Slide 21