The Effect Of MXene Derivative On Hydrogen Ab/desorption Behavior Of NaAlH₄

Light metal complex hydrides are considered as potential hydrogen storage materials because of the high theoretical hydrogen storage capacity compared with others. However, their practical application is limited due to high operating temperatures, sluggish kinetics and strict testing conditions about dehydrogenation and hydrogenation. Therefore, as solid hydrogen storage material, there are many problems to be further solved. The addition of catalyst is one of the most effective method to improve the ab/desorption kinetic of NaAlH₄. The derivatives（MXene-TiO2 and TiC） of Titanium based two dimensional transition metal carbide（MXene） are an ideal additive to improve the hydrogen storage properties of NaAlH₄ because of its controllable microstructure. In this paper, the catalyst behavior of MXene-TiO2 and TiO2-C prepared by solvothermalalchohysis method on NaAlH₄ hydrogen storage was systematically studied.Firstly, the hydrogen evolution properties of NaAlH₄ + x wt% MXene-TiO2（x =0, 5, 10 and 10） were studied. The initial dehydriding temperature and hydrogen desorption capacity gradually decreased with increasing the amount of additive. The best comprehensive performance of hydrogenation storage was obtained when x value was 10. The hydrogen capacity of NaAlH₄ + 10 wt% MXene-TiO2 reached to 1.25wt% within 100 min at 100℃, and it released 4.89 wt% hydrogen within 100 min at140℃. At the same time, the good cycle stability within 5 cycles was observed.Comparing with MXene, A-TiO2, R-TiO2, Ti2O3, TiO and TiC, MXene-TiO2 exhibits better catalytic effect on the hydrogen desorption of NaAlH₄ due to uniform dispersion and the synergistic effect of TiC and TiH2.TiO2-C composite with different microstructure, phase composition and phase abundance were prepared by solvothermalalchohysis, and hydrogen storage performances of NaAlH₄ + 10 wt% TiO2-C were investigated. The efficiency of FS-A0.9R0.1TC is the best. Hydrogen desorption of the NaAlH₄+10 wt % TiO2-Csamples were evaluated by temperature-programmed-desorption via volumetric release. It shows that the intial and terminal dehydrogenation temperature of NaAlH₄ is significantly reduced. Introduction of additives can effectively promote the decomposition of [AlH4]- and [AlH6]3-. It releases 3.1 wt% hydrogen at 90 ℃ within30 min for NaAlH₄ + FS-A0.9R0.1TC. Moreover, it quickly release amount of hydrogen to 4.6 wt% within 20 min at 140 ℃ and almost hydrogen was released within 20 min.At the same time, the good cycle stability within 5 cycles was observed. The theoretical calculation shows that the catalytic activity of US-A0.3R0.7TC and FS-A0.9R0.1TC is higher than ATC or RTC.It due to the interaction of lattice distortion caused by phase transformation.