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# Hydrogen storage properties of nitrogen- and halogen- containing materials

Du Plessis, Rachel Frances (2017)
Ph.D. thesis, University of Birmingham.

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## Abstract

The Li−Mg−N−H system represents a promising system for a solid-state hydrogen store. Kinetic and thermodynamic improvements are required to bring the properties of this system to a suitable position. The effect of preparation conditions and the addition of dopant materials into this system were investigated by a variety of experimental techniques. The preparation method of the sample was found to be very important. The choice of initial preparation and desorption conditions can be used to control the phase of Li$$_2$$Mg(NH)$$_2$$ formed. Pressurised milling conditions (under 100 bar H$$_2$$) appeared to be successful in reducing gas release during milling, but changed the reaction pathway.

The addition of 0.1 mole fraction of either calcium halide dopant, CaCl$$_2$$ or CaBr$$_2$$ lowered the peak hydrogen desorption temperature from this system. The activation energies of all the doped samples were reduced relative to the undoped samples prepared in the same manner.

The reactions between MgH$$_2$$ and NH$$_4$$Cl at various temperatures and stoichiometry’s were also investigated using several techniques. Solid-state reactions between these two reagents have not been carried out before. An unknown set of peaks was observed by powder XRD and a new phase, Mg(NH$$_4$$)$$_2$$Cl$$_4$$ was identified which was found to be iso-structural with Mg(NH$$_4$$)$$_2$$F$$_4$$.

Type of Work: Ph.D. thesis. Anderson, P.A. (Paul Alexander) (1965-) and Read, Mark S. D. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Chemistry Publications arising from thesis: R. F. Bill, D. Reed, D. Book, P.A. Anderson, Effect of the calcium halides, CaCl2 and CaBr2, on hydrogen desorption in the Li-Mg-N-H system, Journal of Alloys and Compounds. 2015, 645, S96-S99 http://dx.doi.org/10.1016/j.jallcom.2014.12.269 QD Chemistry University of Birmingham 7862
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