Dehydrogenation of Surface-Oxidized Mixtures of 2LiBH4 + Al/Additives (TiF3 or CeO2)

Abstract

Abstract:Research for suitable hydrogen storage materials is an important ongoing subject. LiBH 4 -Al mixtures could be attractive; however, several issues must be solved. Here, the dehydrogenation reactions of surface-oxidized 2LiBH 4 + Al mixtures plus an additive (TiF 3 or CeO 2 ) at two different pressures are presented. The mixtures were produced by mechanical milling and handled under welding-grade argon. The dehydrogenation reactions were studied by means of temperature programmed desorption (TPD) at 400 • C and at 3 or 5 bar initial hydrogen pressure. The milled and dehydrogenated materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transformed infrared spectroscopy (FT-IR) The additives and the surface oxidation, promoted by the impurities in the welding-grade argon, induced a reduction in the dehydrogenation temperature and an increase in the reaction kinetics, as compared to pure (reported) LiBH 4 . The dehydrogenation reactions were observed to take place in two main steps, with onsets at 100 • C and 200-300 • C. The maximum released hydrogen was 9.3 wt % in the 2LiBH 4 + Al/TiF 3 material, and 7.9 wt % in the 2LiBH 4 + Al/CeO 2 material. Formation of CeB 6 after dehydrogenation of 2LiBH 4 + Al/CeO 2 was confirmed.

Nanostructured Metal Hydrides for Hydrogen Storage

“…They identified the formation of Al 2 O 3 and Ti 2 O 3 during decomposition of TiCl 3 -doped NaAlH 4 and attributed the enhanced dehydrogenation kinetics to the high hydrogen mobility within these oxides species near the surface. Kato et al and Carrillo-Bucio et al both found that partial oxidation of milled LiBH 4 , either with oxygen or oxide additives and limited to the surface, reduced the activation barrier for dehydrogenation, lowering the observed T dec . , The oxidized samples exhibited additional Li 2 O by XPS following segregation of lithium to the surface, which helped to destabilize LiBH 4 for hydrogen desorption and not release of diborane. These studies suggest that the role of surface oxidation on metal hydride hydrogenation and dehydrogenation kinetics may be far more subtle and complex than has generally been supposed.…”

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

“…In addition, the surface oxidation effects help to reach thermodynamically predicted temperatures for dehydrogenation reactions. 40,42,43 In this study, it is observed that mesoporous NiCo 2 O 4 with a surface oxidized LiBH 4 system presents an outstanding storage performance. Notably, 5.8 wt% of hydrogen was desorbed using a LiBH 4 + 75% NiCo 2 O 4 system in isothermal dehydrogenation at 250 °C for 60 minutes.…”

The Dehydrogenation Mechanism and Reversibility of LiBH4 Doped by Active Al Derived from AlH3

“…Therefore, Al has been popularly employed as another destabilization agent to improve the hydrogen desorption properties of LiBH 4 . The Al source can be either a metallic Al or a complex hydrides containing Al [24][25][26]. However, the metallic Al is usually coated with an oxide layer, which greatly limits the improvement of dehydrogenation and the reversibility of LiBH 4 .…”