Effect of a mesoporous NiCo2O4 urchin-like structure catalyzed with a surface oxidized LiBH4 system for reversible hydrogen storage applications.

A mesoporous NiCo2O4 urchin-like structure was synthesized by applying a facile hydrothermal method. Different concentrations of NiCo2O4 urchin-like structures were mixed with a surface oxidized LiBH4 system using a wet-impregnation method, followed by heat treatment. The hydrogen storage capacity of LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems was investigated. Typically, hydrogenated LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems desorbed 2.85 wt%, 3.78 wt% and 3.91 wt% of hydrogen, respectively, at the dehydrogenation temperature ranging from room temperature (RT) to 275 °C. Further, the LiBH4 + 75% NiCo2O4 system exhibited better kinetics than other systems and released ∼5.8 wt% of hydrogen at a isothermal dehydrogenation temperature of 250 °C in 60 minutes. Hydrogen binding energies were calculated as 0.28 eV, 0.27 eV and 0.26 eV for LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems, respectively. Moreover, the calculated activation energies of LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems are 17.99 kJ mol-1, 17.03 kJ mol-1 and 16.92 kJ mol-1, respectively. The calculated BET (Brunauer-Emmett-Teller) surface area of NiCo2O4 and LiBH4 + 75% NiCo2O4 systems is 124.05 and 136.62 m2 g-1, respectively. These results showed that hydrogen sorption and desorption properties are significantly increased by the influence of mesoporous structure, lower binding energy and activation energy of LiBH4 + 75% NiCo2O4 system.

Single-walled carbon nanotubes/lithium borohydride composites for hydrogen storage: role of in situ formed LiB(OH)4, Li2CO3 and LiBO2 by oxidation and nitrogen annealing.

Lithium Borohydride (LiBH4), from the family of complex hydrides has received much attention as a potential hydrogen storage material due to its high hydrogen energy densities in terms of weight (18.5 wt%) and volume (121 kg H2 per mol). However, utilization of LiBH4 as a hydrogen carrier in off- or on-board applications is hindered by its unfavorable thermodynamics and low stability in air. In this study, we have synthesized an air stable SWCNT@LiBH4 composite using a facile ultrasonication assisted impregnation method followed by oxidation at 300 °C under ambient conditions (SWLiB-A). Further, part of the oxidized sample is treated at 500 °C under nitrogen atmosphere (SWLiB-N). Upon oxidation in air, the in situ formation of lithium borate hydroxide (LiB(OH)4) and lithium carbonate (Li2CO3) on the surface of the composite (SWLiB@LiBH4) is observed. But in the case of SWLiB-N, the surface hydroxyl groups [OH4]- completely vanished leaving porous LiBH4 with SWCNT, LiBO2 and Li2CO3 phases. Hydrogen adsorption/desorption experiments carried out at 100 °C under 5 bar H2 pressure showed the highest hydrogen adsorption capacity of 4.0 wt% for SWLiB-A and 4.3 wt% for SWLiB-N composites in the desorption temperature range of 153-368 °C and 108-433 °C respectively. The observed storage capacity of SWLiB-A is due to the H+ and H- coupling between in situ formed Li+[B(OH)4]-, Li2+[CO3]- and Li+[BH4]-. Whereas in SWLiB-N, the presence of positively charged Li and B atoms and LiBO2 acts as a catalyst which resulted in reduced de-hydrogenation temperature (108 °C) as compared to bulk LiBH4. Moreover, it is inferred that the formation of intermediate phases such as Li+[B(OH)4]-, Li2+[CO3]- (SWLiB-A) and Li+[BO2]- (SWLiB-N) on the surface of the composites not only stabilizes the composite under ambient conditions but also resulted in enhanced de- and re-hydrogenation kinetics through catalytic effects. Further, these intermediates also act as a barrier for the loss of boron and lithium through diborane release from the composites upon dehydrogenation. Furthermore, the role of in situ formed intermediates such as LiB(OH)4, Li2CO3 and LiBO2 on the stability of the composite under ambient conditions and the hydrogen storage properties of the SWCNT@LiBH4 composite are reported for the first time.

Charge mediated room temperature magnetoelectric coupling in Zn1-xSmxO/BaTiO3 bilayer thin film.

We present a room-temperature magnetoelectrically coupled bilayer thin film multiferroic system (BTS) 'Zn1-xSmxO/BaTiO3 (where x = 0.02 and 0.04)' grown on a SrTiO3 (100) substrate. The thin film layers are polycrystalline and continuous with an average roughness of 3.2 nm. At room temperature, the BTSs with x = 0.02 (BTS2) and x = 0.04 (BTS4) are ferromagnetic with a saturation magnetic moment (Ms) of 5.1 memu and 8.6 memu respectively, while the latter shows a paramagnetic trace. Both BTS2 and BTS4 are ferroelectric at room temperature with a saturation polarization (Ps) of 12.51 µC cm(-2) and 6.75 µC cm(-2), respectively. The coercive (electric) field required to polarize BTSs increases as a function of x (25.2 kV cm(-1) for BTS2 and 62.3 kV cm(-1) for BTS4). The change in degree of polarization/magnetization (domain contrast of the piezoresponse/magnetic force microscopy images), permittivity and resistance, as a function of external magnetic/electric field, directly suggests that the Zn0.98Sm0.02O/BaTiO3 BTS is magnetoelectrically coupled at room temperature.