Characterization of Materials for a Hydrogen-Based Economy by Cold Neutron Prompt Gamma-Ray Activation Analysis
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Characterization of Materials for a Hydrogen-Based Economy by Cold Neutron Prompt Gamma-Ray Activation Analysis Rick Paul, and Lei Raymond Cao Analytical Chemistry Division, NIST, 100 Bureau Drive, MS 8395, Gaithersburg, MD, 20899 Characterization of Materials for a Hydrogen-Based Economy by Cold Neutron Prompt Gamma-Ray Activation Analysis†Rick L. Paula, Lei R. Caoa,b a
Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 b Department of Materials Science & Engineering, University of Maryland, College Park, MD 20742
ABSTRACT An instrument for cold neutron prompt gamma-ray activation analysis (PGAA) at the NIST Center for Neutron Research (NCNR) has proven useful for the chemical characterization of hydrogen storage materials and other materials of importance to a hydrogen-based economy. The detection limit for hydrogen is less than 10 mg/kg for most materials. Potential hydrogen storage materials that have been characterized by PGAA include single-wall carbon nanotubes with and without boron doping, porous carbons, lithium magnesium imides, and ternary hydrides of various elements. The capability to allow in situ hydrogenation and characterization of materials is currently under development. PGAA has also been used to characterize materials used in hydrogen fuel cells, including solid proton conductors, polymer membrane, and proton exchange membranes. Future upgrades to the instrument will improve detection limits and functionality of the instrument.
INTRODUCTION Establishing a hydrogen-based economy means overcoming challenges in the areas of hydrogen production, transport, storage, and fuel cell development. Improving the state of the art of hydrogen storage materials requires accurate measurement of hydrogen uptake and release under different temperature/pressure conditions as well as knowledge of elemental composition and impurities that may enhance or detract from the hydrogen storage capacities. Efficient design of fuel cells requires optimizing the composition of materials used for cell membranes. Methods are also needed to diagnose â€
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problems in fuel cells, such as leaching of contaminants from electrodes into cell membranes during fuel cell operation. Prompt gamma-ray activation analysis (PGAA) is a nondestructive multielemental analysis technique that is suitable for many of these applications. When samples are irradiated in a beam of neutrons, nuclei of many elements undergo neutron capture and emit prompt gamma rays during de-excitation. Measurement of the energies and intensities of these gamma rays yields quantitative and qualitative analysis. Although PGAA is capable of measuring most elements, it is particularly useful for the determination of light elements (e.g., H, B, N, C) that are not easily measurable by other techniques. PGAA is one of the few techniques capable of nondestructive measurement of hydrogen at low levels. The techn
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