Reversible Hydrogen Storage Battery Materials NonDestructive Sensor Development
Reversible Hydrogen Storage Battery Materials: Non-Destructive Sensor Development A. N. Lasseigne-Jackson 1, B. Mishra 2, D. L. Olson 2, and J. E. Jackson 2 1. National Institute of Standards and Technology 2. Colorado School of Mines
Outline • Introduction – Free Electron Theory – Thermoelectric Power – Hydrogen Storage Materials • Investigations – Characterization of La. Ni 5 Utilizing Thermoelectric Power – Characterization of Na. Al. H 4 Utilizing Thermoelectric Power • Optimization of Thermoelectric Power Measurements • Final Conclusions
Free Electron Theory • The free electron model assumes valence electrons of constituent atoms become conduction electrons and move freely through the volume of the metal • A conduction electron is scattered by perturbations in periodicity like lattice defects, impurities, phonons, etc. • Certain properties of a metal can be determined from the electron gas properties • The properties of metals are determined from: – The occupation of the valence and conduction bands – The spacing between the valence and conduction bands – Relative location of the Fermi energy
Free Electron Theory • The highest electronic energy state assumed by an electron at absolute zero is the Fermi energy:
Fermi-Dirac Energy Distribution
Thermoelectric Power Measurements
Thermoelectric Power Measurements S r h K n me Thermoelectric power Scattering parameter Planck constant Boltzmann's constant Free electron concentration Effective mass (m*) S = S(n, me, r)
Use of the Effective Mass of an Electron • Electron wave function is modified by localized potentials • Free Electron Wave (-----) + Localized Potential Ref: Wilkes, 1973 LCAO Model
Thermoelectric Power
Electronic Nature of Hydrogen
Schematic Pressure-Composition-Temperature Diagram
Comparison of Thermoelectric Power and Activity Diagrams
Pressure-Composition Isotherms for La. Ni 5 Van Vucht et al. , 1970
Hydrogen Charging System www. leco. com
Thermoelectric Power Powder Measurement System Powder Sample
Thermoelectric Power as a Function of H/La. Ni 5
Thermoelectric Power as a Function of H/La. Ni 5
Sodium Alanates o o 5. 6 % Hydrogen by Weight $50 per kg Slow Kinetics Reversible only at ~600 K Bogdanovic and Sandrock, 2002
PCT Diagram for Na. Al. H 4 Bogdanovic et al. , 2000
Thermoelectric Power as a Function of H/Al
Thermoelectric Power as a Function of H/Al Bogdanovic et al. , 2000
Optimization of Thermoelectric Power Measurements • • Equipment Design of Probes Calibration and Standardization Temperature Difference
Determination of Optimum Temperature Difference 1. 7 ppm 0. 9 ppm 0. 3 ppm
Outlook • Resistivity is also dependent upon effective mass allowing inductive impedance to be used to assess hydrogen content and to obtain thermodynamic data. • Magnetic properties, especially for transition metal containing hydrogen storage materials, has a strong correlation to hydrogen content.
Conclusions • The use of electronic and magnetic properties will give new insight into the behavior of hydrogen storage materials. • Advanced elastic property measurements will also give insight into the behavior of hydrogen storage materials. • Since these properties are dependent on many physical variables, it will require a combination of techniques to develop a reliable, rapid measurement system.
Acknowledgements • The authors would like to thank and acknowledge the support of the Naval Research Laboratories and the University of Hawaii
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