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An outstanding effect of graphite in nano-MgH2-TiH2 on hydrogen storage performance

Abstract

TiH2–modified MgH2 was prepared by high energy reactive ball milling (HRBM) of Mg and Ti in hydrogen and showed high weight H storage capacity and fast hydrogenation / dehydrogenation kinetics. However, decrease in the reversible H storage capacity on cycling at high temperatures takes place and is a major obstacle for its use in hydrogen and heat storage applications. Reversible hydrogen absorption / desorption cycling of the materials requires use of the working temperature ≥330 °C and results in a partial step-by-step loss of the recoverable hydrogen storage capacity, with less significant changes in the rates of hydrogenation / dehydrogenation. After hydrogen desorption at 330–350 °C, hydrogen absorption can proceed at much lower temperatures, down to 24 °C. However, a significant decay in the reversible hydrogen capacity takes place with increasing number of cycles. The observed deterioration is caused by cycling-induced drastic morphological changes in the studied composite material leading to a segregation of TiH2 particles in the cycled samples instead of their initial homogeneous distribution. However, introduction of 5 wt.% of graphite into the MgH2 – TiH2 composite system prepared by HRBM leads to an outstanding improvement of the hydrogen storage performance. Indeed, hydrogen absorption and desorption characteristics remain stable through the 100 hydrogen absorption / desorption cycles and are related to an effect of the added graphite. TEM study showed that carbon is uniformly distributed between the MgH2 grains covering segregated TiH2, preventing the grain growth and thus keeping unchanged the reversible storage capacity and the rates of hydrogen charge and discharge. Modelling of the kinetics of hydrogen absorption and desorption in the Mg–Ti and Mg–Ti–C composites showed that the reaction mechanisms significantly change depending on presence or absence of graphite, number of absorption-desorption cycles and operating temperature.

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Publication details

The article was received on 30 Mar 2018, accepted on 30 Apr 2018 and first published on 02 May 2018


Article type: Paper
DOI: 10.1039/C8TA02969E
Citation: J. Mater. Chem. A, 2018, Accepted Manuscript
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    An outstanding effect of graphite in nano-MgH2-TiH2 on hydrogen storage performance

    M. V. Lototskyy, R. V. Denys, V. A. Yartys, J. Eriksen, J. Goh, S. Nyallang Nyamsi, C. Sita and F. Cummings, J. Mater. Chem. A, 2018, Accepted Manuscript , DOI: 10.1039/C8TA02969E

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