Titanium Hydride Nanoplates Enable 5 wt% of Reversible Hydrogen Storage by Sodium Alanate below 80°C

Sodium alanate (NaAlH4) with 5.6 wt% of hydrogen capacity suffers seriously from the sluggish kinetics for reversible hydrogen storage. Ti-based dopants such as TiCl4, TiCl3, TiF3, and TiO2 are prominent in enhancing the dehydrogenation kinetics and hence reducing the operation temperature. The tradeoff, however, is a considerable decrease of the reversible hydrogen capacity, which largely lowers the practical value of NaAlH4. Here, we successfully synthesized a new Ti-dopant, i.e., TiH2 as nanoplates with ~50 nm in lateral size and ~15 nm in thickness by an ultrasound-driven metathesis reaction between TiCl4 and LiH in THF with graphene as supports (denoted as NP-TiH2@G). Doping of 7 wt% NP-TiH2@G enables a full dehydrogenation of NaAlH4 at 80°C and rehydrogenation at 30°C under 100 atm H2 with a reversible hydrogen capacity of 5 wt%, superior to all literature results reported so far. This indicates that nanostructured TiH2 is much more effective than Ti-dopants in improving the hydrogen storage performance of NaAlH4. Our finding not only pushes the practical application of NaAlH4 forward greatly but also opens up new opportunities to tailor the kinetics with the minimal capacity loss.

Influence of Nanoconfinement on the Hydrogen Release Processes from Sodium Alanate

Sodium alanate (NaAlH4) is a prospective H2 storage material for stationary and mobile applications, as NaAlH4 contains 7.4 wt% of H2, and it is possible to do multiple H2 release and accumulation cycles. Nanoconfinement is a potential solution to enhance the H2 release properties of NaAlH4. To optimize the supporting material and the synthesis method used for the nanoconfinement of NaAlH4, a better understanding of the influence of nanoconfinement on the H2 release processes is necessary. Thus, the H2 release from bulk, purely nanoconfined, and intermediate NaAlH4 is measured at different temperature ramp rates, and the characteristic parameters for each hydrogen release process are determined. Activation energies for each process are determined using the Kissinger method, and the effect of nanoconfinement on the activation energies is analysed. The impact of nanoconfinement on the H2 release processes from NaAlH4 and the limitations of each process in case of bulk and nanoconfined NaAlH4 are presented and discussed. Nanoconfinement of NaAlH4 decreases activation energies of the initial reversible H2 release steps to between 30 and 45 kJ mol−1 and increased the activation energy of the last irreversible H2 release step to over 210 kJ mol−1.

Sodium Alanate Dehydrogenation Properties Enhanced by MnTiO3 Nanoparticles

In this study, we investigated the influence of MnTiO3 nanoparticles additive on hydrogen released performance of NaAlH4 for the first time. The MnTiO3 nanoparticles were successfully synthesized using conventional solid-state ceramic route. It was found that the hydrogen released performance of NaAlH4 can be significantly improved by the addition of MnTiO3 nanoparticles. Meantime, the composite of NaAlH4 doped 5 wt% MnTiO3 possessed excellent dehydrogenation properties, the onset dehydrogenation temperature was only 70.6 °C, reduced by about 105 °C in comparison with the pristine NaAlH4, and approximately 5.01 wt% of hydrogen could be released from composite with temperature heated to 220 °C. The isothermal dehydrogenation test results indicated that the amount of hydrogen released by NaAlH4-5 wt% MnTiO3 composite could reach 4.4 wt% under 200 °C within 25 min. According to the analysis of X-ray diffraction, the presence of MnTiO3 nanoparticles did not alter the overall dehydrogenation pathway of NaAlH4, and the Al3 Ti phases formed after dehydrogenation, which enhanced hydrogen desorption performances of NaAlH4 .