Reversibility of Al/Ti Modified LiBH₄

Abstract

Lithium borohydride has a high reversible hydrogen storage capacity. For its practical use as an onboard hydrogen storage medium in mobile applications, the temperature and pressure conditions along with the kinetics of the hydrogenation/dehydrogenation cycles have to be improved. Lithium borohydride can be modified by ball-milling with Al-and/or Ti-containing compounds. In this study, lithium alanate (LiAlH 4 ), is used as an Al source. From careful examination of the ball-milled samples, it appears that LiBH 4 remains unchanged during milling. The samples contain ∼100 nm diameter Al and/or Al-Ti solid solution (ss) crystallites. When used alone, Ti has a limited effect whereas Al is shown to be active, lowering the temperature of decomposition and increasing the desorption rate and reversibility at moderate temperature and pressure (85 bar, 350°C). During cycling, AlB 2 is formed in the dehydrogenated state and disappears in the hydrogenated state; its formation increases the stability of the products and thus results in a lower desorption temperature. The Al-Ti (ss) also allows a slow release of hydrogen at very low temperatures (200°C).

Complex and liquid hydrides for energy storage

“…Unfortunately, these systems have a significant loss in capacity upon cycling, depending on the catalysts as well as the preparation method used [185,194,195,197]. This may be diffusion related, as LiH, AlB 2 and B are physically apart and unable to reform into LiBH 4 and Al, or there may be a formation of a boride shell on the surface of the Al particles, preventing the complete reaction of Al and B into AlB 2 [197], as seen in Fig.…”

“…8). Several studies [182][183][184] report catalytic activity of additives in LiBH 4 ; however, the result of doping LiBH 4 with TiCl 3 is not the formation of a totally reversible hydrogen storage system [185]. Recently, the formation of a volatile Ti(BH 4 ) 3 on the surface of the sample during the metathesis TiCl 3 ?…”

Ionic conductivity and the formation of cubic CaH2 in the LiBH4–Ca(BH4)2 composite

“…All above-mentioned crystalline solid electrolytes have considerably lower Li + conductivities, with the exception of Li 10 GeP 2 S 12 which has a Li + conductivity of 12 m/S/cm at 27°C [13]. Lithium borohydride has been investigated extensively in recent years, both as a hydrogen storage material [18][19][20][21][22][23] and as a crystalline solid electrolyte material for lithium batteries [24][25][26]. It is lightweight (0.666 g/cm 3 ) and has been shown to be electrochemically stable up to 5 V [27].…”

Improved Dehydrogenation Properties of Calcium Borohydride Combined with Alkaline-Earth Metal Amides

“…34 Furthermore, a broadened peak related to BÀH band was narrowed for Ca(BH 4 ) 2 À2Mg(NH 2 ) 2 and Ca(BH 4 ) 2 À2Ca(NH 2 ) 2 in comparison with pristine Ca(BH 4 ) 2 , even though no hydrogen or ammonia was released from the mixture during ball-milling treatment. Because FTIR results cannot tell the detailed differences of BÀH bond for ball-milled samples, 11 B MAS NMR spectra were performed on Ca(BH 4 ) 2 À2Mg(NH 2 ) 2 , Ca(BH 4 ) 2 À 2Ca(NH 2 ) 2 , and pristine Ca(BH 4 ) 2 , which are shown in Figure 2 Only one distinct peak of hydrogen evolution can be observed at 360°C in the MS curve of pristine Ca(BH 4 ) 2 , without any detectable diborane and ammonia signal in the MS tracks within the temperature range (20À500°C). The total desorption capacity up to 480°C is 3 equiv or 8.6 wt % hydrogen (Figure 4).…”