Complex Ammine Titanium(III) Borohydrides as Advanced Solid Hydrogen-Storage Materials with Favorable Dehydrogenation Properties

Abstract

Ammine metal borohydrides (AMBs), with high hydrogen contents and favorable dehydrogenation properties, are receiving intensive research efforts for their potential as hydrogen storage materials. In this work, we report the successful synthesis of three ammine titanium borohydrides (denoted as ATBs), Ti(BH 4 ) 3 •5NH 3 , Li 2 Ti-(BH 4 ) 5 •5NH 3 , and Ti(BH 4 ) 3 •3NH 3 via metathesis reaction of metal chloride ammoniates (TiCl 3 •5NH 3 and TiCl 3 •3NH 3 ) and lithium borohydride. These ATBs present favorable stability, owing to the coordination with NH 3 groups, compared to the unstable Ti(BH 4 ) 3 at room temperature. Dehydrogenation results revealed that Ti(BH 4 ) 3 •5NH 3 , which theoretically contains 15.1 wt % hydrogen, is able to release ∼13.4 wt % H 2 plus a small amount of ammonia. This occurred via a single-stage decomposition process with a dehydrogenation peak at 130 °C upon heating to 200 °C. For Li 2 Ti(BH 4 ) 5 •5NH 3 , a three-step decomposition process with a total of 15.8 wt % pure hydrogen evolution peaked at 105, 120, and 215 °C was observed until 300 °C. In the case of Ti(BH 4 ) 3 •3NH 3 , a release of 14 wt % pure hydrogen via a two-step decomposition process with peaks at 109 and 152 °C can be achieved in the temperature range of 60−300 °C. Isothermal TPD results showed that over 9 wt % pure hydrogen was liberated from Ti(BH 4 ) 3 •3NH 3 and Li 2 Ti(BH 4 ) 5 •5NH 3 within 400 min at 100 °C. Preliminary research on the reversibility of this process showed that dehydrogenated ATBs could be partly recharged by reacting with N 2 H 4 in liquid ammonia. These aforementioned preeminent dehydrogenation performances make ATBs very promising candidates as solid hydrogen storage materials. Finally, analysis of the decomposition mechanism demonstrated that the hydrogen emission from ATBs is based on the combination reaction of B−H and N−H groups as in other reported AMBs.

Tailoring the Properties of Ammine Metal Borohydrides for Solid‐State Hydrogen Storage

“…Future research may also address this issue, for example, by detailed analysis of the reaction mechanism for hydrogen absorption of dehydrogenated nanoconfined Al(BH 4 ) 3 ·6NH 3 treated with hydrazine in liquid ammonia similar to other B-N based materials. [24,[57][58][59][60][61] …”

Three-dimensional metal-intercalated covalent organic frameworks for near-ambient energy storage

“…U.S. Department of Energy (DOE) set a target for practical H storage materials to have a gravimetric capacity of 5.5 wt% by 20174. The challenge is to dramatically increase storage capacity and reversibility at ambient conditions5. Carbon-based nanostructures and porous materials including fullerene, nanotube, and carbyne networks, have been proposed as potential H 2 storage media, thanks to their high surface-to-weight ratios, good reversibility and fast kinetics678910.…”

Removal or storage of environmental pollutants and alternative fuel sources with inorganic adsorbents via host–guest encapsulation

“…These results led the authors to speculate that the chemisorption of H2 in these compounds might be reversible at temperatures lower than those of other types of hydrides, rendering such hydrides a potentially new class of intermediate -temperature hydrides. Furthermore, investigations on Ti(BH4)3·3NH3, Ti(BH4)3·5NH3, and Li2Ti(BH4)5·5NH3 by Yuan et al (2012) 219 revealed that high H2 adsorption capacities below T = 300 °C are possible. Especially noteworthy is the continuous release of H2 by Li2Ti(BH4)5·5NH3 and Ti(BH4)3·3NH3 at a constant temperature of T = 100 °C, with H2 adsorption capacities of ~ 9 wt%, which fulfills the requirements for vehicular applications.…”