Materials designing of metal borohydrides: Viewpoints from thermodynamical stabilities

Abstract

Double-cation borohydrides MLi m−n (BH 4 ) m (M = Zn, n = 2; M = Al, n = 3; M = Zr, n = 4; n ≤ m) were expected to be synthesized and their thermodynamical stabilities were also examined experimentally. The samples with the compositions of ZnLi(BH 4 ) 3 and AlLi(BH 4 ) 4 disproportionate into Zn(BH 4 ) 2 -(or Al(BH 4 ) 3 -) and LiBH 4 -based phases upon heating, respectively. However, no disproportionation reaction is observed in ZrLi m−4 (BH 4 ) m (m = 5 and 6). It should be emphasized that hydrogen desorption temperature T d of ZrLi m−4 (BH 4 ) m continuously increases from 440 to 650 K as the composition m increases from 4 to 6, and approaches to 740 K (T d of LiBH 4 ). The experimental results indicate that the combination of appropriate cations is an effective method to adjust the thermodynamical stabilities of metal borohydrides, similar to the conventional "alloying" method for hydrogen storage alloys.

First-principles studies of phase stability and crystal structures in Li-Zn mixed-metal borohydrides

“…The thermodynamic stability of binary metal hydrides has been found to be inversely related to the metal electronegativity 8 . A similar relationship for borohydrides has been theoretically as well as experimentally investigated 1,9,10 . Unfortunately, efforts to tackle the drawbacks of the single cation borohydrides have not been completely successful.…”

“…Inspired by the hypothesis that it may be possible to precisely adjust the thermal stabilities of borohydrides by a careful choice of double-or multications, Li et al 10 experimentally examined the thermodynamic stabilities of MLi m-n (BH 4 ) m (M=Zn, n=2; M=Al, n=3; M=Zr, n=4; n≤m). Also,Černý et al have experimentally studied Mg x Mn (1-x) (BH 4 ) 2 (x=0-0.8) 12 .…”

Recent Progress in Metal Borohydrides for Hydrogen Storage

“…Inspired by this finding, an approach of producing multi cation borohydrides MM'(BH 4 ) n , in which M and M' have different electronegativities has been proposed to precisely tailor the thermodynamic stability [107]. Several [120].…”

Theoretical and experimental study on Mg(BH4)2–Zn(BH4)2 mixed borohydrides

“…Different approaches have been used to de-stabilize pure complex hydrides: anion substitution, cation substitution with mixed metal borohydrides formation, nanoconfinement and reactive hydride composites [1][2][3]. Since the first report [4], anion substitution has been suggested as a promising method to favor the thermodynamics of hydrogen sorption in complex hydrides [5][6][7][8][9][10][11][12][13][14].…”