Nanocomposites and nanomaterials

The MAX-phase Ti3AlC2 as a catalyst for improving of hydrogen storage properties of Mg
Kirian I.M., Lakhnik A.M., Rud A.D.
G.V. Kurdyumov Institute for Metal Physics NAS of Ukraine.
Academician Vernadsky Boulevard, 36, Kiev 03142, Ukraine
E-mail: kiryan.inna@gmail.com

The most promising material for hydrogen storage is magnesium, which can absorb up to 7.67% hydrogen. The main disadvantages that must be overcome at use of magnesium are the high temperature at which the sorption-desorption of hydrogen occurs and the slow hydrogen kinetics. One of the methods that allows to improve the kinetics of sorption-desorption of hydrogen is mechanoactivation treatment of magnesium with various additives. Further development of this approach is the use of new type of catalysts - MAX phases.
The MAX-phase Ti3AlC2 was synthesized in G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine by sintering method [1]. The powders Ti3Al1.1C2+5 wt% B2O3 were homogenized, cold-pressed under 640 MPa and sintered at 1400 °C during 1 hr. The phase analysis shows that the synthesized material contains ~98.5 wt% of Ti3AlC2 phase and ~ 1.5 wt% TiC.
Samples with Mg-5 wt% Ti3AlC2 compositions were prepared by ball milling under hydrogen atmosphere at 400 rpm for 10 hr. Initial hydrogen pressure in ball-mill container was ~ 0.5 MPa. Every two hours, the grinding process was stopped and a new portion of gas was added. This approach allowed the control of the hydrogen absorption process. During grinding, the mixture exhibited high activity of interaction with hydrogen. After 10 hours of ball-milling the results of the X-ray diffraction analysis show that the percentage of MgH2 in the sample is ~ 80 %. The study of sorption properties of the sample was carried out under conditions continuous heating. It was established that desorption of hydrogen begins at a temperature of ~ 210 °Ñ. After complete desorption, the sample was re-heated in an atmosphere of hydrogen. It was established that Mg-5 wt% Ti3AlC2 composite begins absorb hydrogen at a temperature of ~ 95 °Ñ. As a result of cycling, the temperature of desorption has shifted towards lower values ~ 186 °C. Thus, the use of the MAX-phase Ti3AlC2 as a catalyst to magnesium during reactive mechanoactivation leads to the formation of a composite with enhanced hydrogen sorption properties in comparison with pure magnesium.
1.	Rud A.D., Lakhnik A.M., Kirian I.M., [at al.] Mechanochemical synthesis and structure of metal-carbon composites based on the MAX-phases // Materials Today: Proceedings. – 2018. – 5. – P. 26084–26088.