Development of Combined Optical Cell and Sieverts-type Apparatus for in-situ Measurement of Hydrogen Storage Materials
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Development of Combined Optical Cell and Sieverts-type Apparatus for in-situ Measurement of Hydrogen Storage Materials C. Chiu1, J. R. Hattrick-Simpers1, E. J. Heilweil2 and L.A. Bendersky1 1 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA 2 Physics Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA ABSTRACT A parallel high-sensitivity hydrogen sorption, and in situ Raman/IR emissivity measurement system has been developed using a stainless-steel sample cell with a sapphire window to act as a bridge between the PCT and optical measurements. The cell can be pressurized up to 4.5 MPa and heated up to 723 K. The system can measure small changes in hydrogen content, down to 0.5 µg, allowing for characterization of small quantities of powers and thin films. Hydrogen desorption in LiNH2 - LiBH4 - MgH2 nanocomposites has been studied by in-situ Raman and PCT measurement, while that of MgH2 powers and thin films has been studied by in-situ PCT and IR emissivity. In powder samples, qualitative trend is observed between changes in the Raman peak intensity/IR emissivity and the amount of hydrogen absorbed or desorbed. INTRODUCTION Development of hydrogen storage materials to satisfy DOE goals in terms of weight capacity, release temperature, charging/discharging rates and cycle life has triggered an intensive search for new or improved light-weight hydrides [1-4]. Traditionally, studying hydrogen storage materials relies on synthesizing bulk samples and measuring hydriding/dehydriding reactions with a Sieverts-type apparatus, which records absorption/desorption kinetics curves or pressureconcentration isotherms (PCTs) [3-8]. Although PCT method provides in-depth results, it is time consuming and not well suited for rapid identification of new materials. To reach the DOE’s milestones a more rapid and comprehensive study of phase space is necessary. The combinatorial method, in which a large number of samples are synthesized in a single experiment, and then characterized in parallel, has the potential to expedite the discovery of novel hydrogen storage materials. However, to date only a few groups have adopted this methodology [9-13]. The hesitance to adopt this new approach is believed to be due to the lack of reliable and quantitative screening techniques. In order for the high-throughput screening of hydrogen storage materials to be feasible, measurements of secondary properties with a one-toone correlation with hydrogen content are required. For this reason a few techniques, such as deflection of cantilever arrays [9], nanocalorimetry [10], and optical imaging [11-13] have been studied to screen combinatorial arrays for their hydrogen sorption properties. Normalized infrared emissivity (NIRE) and Raman spectroscopy are two measurements with potential to be high-throughput screening techniques. Recently, we have shown, through studies of in-situ hydrogenation of Mg – Ni combinatorial films, that NIRE i
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