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TiCr 2 with a body-centered-cubic (BCC) structure was synthesized successfully by mechanical alloying (MA) of elemental powders and mechanical grinding (MG) of as-cast ingots. The formation mechanisms of the TiCr 2 were investigated using X-ray diffraction (XRD) analysis. The thermal stability and hydrogen ab/desorption kinetics were studied using a differential scanning calorimetry (DSC) and a volumetric method. The results showed that the formation mechanisms of TiCr 2 in mechanical alloying and mechanical grinding were different. Mechanical alloying is superior to mechanical grinding in processing TiCr 2 alloy for hydrogen storage. D

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Metal hydrides have recently been proposed for not only hydrogen storage materials but also high-efficiency thermal storage materials. NaMgH3 contains a considerable theoretical thermal storage density of 2881 kJ/kg. However, its sluggish de/re-hydrogenation reaction kinetics and poor cycling stability exhibit unavailable energy efficiency. Doping with active catalyst into NaMgH3 is deemed to be a potential strategy to mitigate these disadvantages. In this work, the enhancement of de/re-hydrogenation kinetics and cycling properties of NaMgH3 is investigated by doping with lamellar-structure 2D carbon-based MXene, Ti3C2. Results shows that introducing 7 wt.% Ti3C2 is proved to perform excellent catalytic efficiency for NaMgH3, dramatically reducing the two-step hydrogen desorption peak temperatures (324.8 and 345.3 °C) and enhancing the de/re-hydrogenation kinetic properties with the hydrogen desorption capacity of 4.8 wt.% H2 within 15 min at 365 °C and absorption capacity of 3.5 wt.% H2 within 6 s. Further microstructure analyses reveal that the unique lamellar-structure of Ti3C2 can separate the agglomerated NaMgH3 particles homogeneously and decrease the energy barriers of two-step reaction of NaMgH3 (114.08 and 139.40 kJ/mol). Especially, lamellar-structure Ti3C2 can improve the reversibility of hydrogen storage of NaMgH3, rendering 4.6 wt.% H2 capacity remained after five cycles. The thermal storage density of the composite is determined to be 2562 kJ/kg through DSC profiles, which is suitable for thermal energy storage application.

NaMgH3 has been considered to be a potential candidate for solid-state hydrogen storage due to its considerable hydrogen gravimetric (6.0 wt %) and volumetric (88.0 g/L) densities. Meanwhile, NaMgH3 possesses an outstanding theoretical thermal storage density of 2881 kJ/kg, which makes it one of the most promising thermal energy storage materials. However, the sluggish dehydrogenation kinetics of NaMgH3 embarrasses further practical application. Doping a nanosize Ti-based catalyst is treated to be one of the most effective methods to settle the poor dehydriding kinetics. In this work, different kinds of TiO2 catalysts, the 5 wt % TiO2 microparticle (MP) (100 nm), TiO2 nanoparticle (NP) (5–10 nm), and TiO2 nanotube (NT) (5–10 nm), were doped into NaMgH3 in the process of ball milling and heat treatment, which in situ formed Na0.46TiO2 significantly promoting the full hydrogen desorption kinetics of NaMgH3. Among all samples, the TiO2 NT-doped sample shows the best performance of which the onset decomposition temperature is reduced to 300 °C, and the first- and second-step decomposition peak temperatures are decreased to 346.3 and 355.8 °C, respectively. The TiO2 NT-doped sample desorbs approximately 3.4 wt % H2 at 350 °C within 10 min, while the pure NaMgH3 sample releases only 0.2 wt % H2 in 10 min. The significant improvement in both two decomposition reactions kinetics of NaMgH3 can be attributed to the tubular morphology of the TiO2 NT and the in situ formation of multivalence Ti species (Na0.46TiO2). These two reasons can change the kinetic models of NaMgH3 from A2 to R2 and further dramatically decrease the activation energies of first- and second-step decomposition reactions of NaMgH3 to 91.7 and 142.1 kJ/mol, respectively. In particular, the in situ formed Na0.46TiO2 can benefit the e– transfers among Na+, Mg2+, and H–, tremendously enhancing dehydrogenation properties.