Sodium alanate in-situ doped with Ti2C MXene with enhanced hydrogen storage properties

Abstract

NaAlH4 is a reversible hydrogen storage material and has attracted great attention recently. However, the application of NaAlH4 in hydrogen storage still has great difficulties. In this study, 2D MXene Ti2C-doped NaAlH4 samples were prepared in-situ by reaction ball milling of NaH under moderate condition. TPD measurement results show that all the as-prepared samples exhibit good thermodynamic performance except for the sample doped with 1 wt% Ti2C. And DSC analysis results show that at the heating rate of 5 K/min, the first and second dehydrogenation peak temperatures of the sample doped with 7 wt% Ti2C were 127.1 °C and 150.6 °C respectively, which are 57.4 °C and 123.6 °C lower than those of pure NaAlH4 (after ball milling), respectively. Meanwhile, NaH/Al-7 wt.% Ti2C sample displays a superior kinetics behavior. Isothermal hydrogen evolution curves show that NaH/Al-7 wt.%Ti2C released 5.21 wt% H2 within 30 min at 150 °C and then absorbs 5.2 wt% H2 in 90 s at 120 °C. Even at a lower temperature of 80 °C, the sample still absorbed 4.71 wt% H2 within 60 min. In addition, almost no release capacity attenuation was observed for NaH/Al-7 wt.%Ti2C after 10 hydrogen absorption/desorption cycles. The improvement of the hydrogen storage properties can be ascribed to the high reactivity of NaAlH4 produced in situ and catalysis of lamellar Ti3+/0 species formed by the reduction of high valent Ti in Ti2C during ball milling.