Hydrogen storage properties of nitrogen- and halogen- containing materials

Du Plessis, Rachel Frances (2017). Hydrogen storage properties of nitrogen- and halogen- containing materials. University of Birmingham. Ph.D.

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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:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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