Proposed Mechanisms for the Catalytic Activity of Ti in NaAlH<sub>4</sub>

Frankcombe, Terry J.

doi:10.1021/cr2001838

Cited by 111 publications

(127 citation statements)

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“…In order to overcome the thermodynamic and kinetic limitations of the thermal decomposition of borohydrides, several novel strategies, such as catalytic doping, 13 nano-engineering, 14 additive destabilization, 15 and chemical modification, 16 have been employed in the past decade, One of the most fascinating strategies is to combine the borohydrides with H δ+ enriched nitrogen-containing compounds such as amide, guanidinium, and NH 3 to form new boron and nitrogen based compounds or composites. [17][18][19][20][21][22][23] The B-N-H materials contain both hydridic and protic hydrogens, and are therefore expected to release hydrogen under more mild conditions, since a local combination of the N−H δ+ ···H δ-−B dihydrogen bonds will be achieved in these materials upon heating.…”

Section: Introductionmentioning

confidence: 99%

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Mao

Guo

et al. 2015

J. Mater. Chem. A

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. (2015). Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior. Journal of Materials Chemistry A, 3 (21), 11269-11276. Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior AbstractMetallic borohydride hydrazinates are novel boron-and nitrogen-based materials that appear to be promising candidates for chemical hydrogen storage. Herein, sodium borohydride hydrazinates, including NaBH 4 ·N2H 4 and NaBH 4 ·2N 2 H 4 , were synthesized via a facile solution synthesis approach based on the solid-liquid reaction between NaBH 4 and hydrazine in tetrahydrofuran (THF) solution. The crystal structure of NaBH 4 ·2N 2 H 4 was solved to a monoclinic structure with unit cell parameters a = 8.4592(2) Å, b = 11.7131(2) Å, c = 6.4584(1) Å, and β = 100.0777(14)°, with space group A1a1 (9). Each Na + ion interacts with four neighboring N 2 H 4 molecules, leading to the formation of Na 4 [N 2 H 4 ] 4 4+ cationic chains along the a direction. Such cationic chains are surrounded by BH 4 − anions. The NaBH 4 ·xN 2 H 4 (x = 1, 2) was characterized by Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectroscopy (MS) to obtain a full picture of the relationship of the structure to the decomposition, which will be useful for future work on borohydride hydrazinates or the study of other B-N materials. Furthermore, magnesium borohydride hydrazinates were synthesized by ball milling the sodium borohydride hydrazinates with magnesium borohydride, and their thermal decomposition was investigated as well. differential scanning calorimetry (DSC), and mass spectroscopy (MS) to obtain a full picture of the relationship of the structure to the decomposition, which will be useful for future work on borohydride hydrazinates or the study of other B-N materials.Furthermore, magnesium borohydride hydrazinates were synthesized by ball milling the sodium borohydride hydrazinates with magnesium borohydride, and their thermal decomposition was investigated as well.

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Section: Introductionmentioning

confidence: 99%

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Mao

Guo

et al. 2015

J. Mater. Chem. A

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“…[6][7][8] This finding triggered extensive research using a multitude of experimental and theoretical methods to unravel the mechanism of the formation and decomposition processes -and as such NaAlH 4 can be considered as a model system to test scientific hypotheses explaining complex gas-solid interactions. 9 In particular, many models have been proposed regarding the catalytic activity of Ti in NaAlH 4 , and these models can be divided into two categories: the ones that claim this activity to come from the bulk, e.g. Refs.…”

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confidence: 99%

“…9,29,30 The temperatures for hydrogen desorption are significantly reduced by the addition of a few mol. % of Ti catalyst.…”

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confidence: 99%

“…% of Ti catalyst. 9 The hydrogen from NaH is only desorbed at high temperatures at technically relevant pressures (698 K at 1 bar 31 ). NaAlH 4 , Na 3 AlH 6 and NaH are ionic compounds, while hydrogen and Al are not.…”

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confidence: 99%

“…After doping reaction, the oxidation state seems to be near Ti(0) as derived from various techniques (e.g. X-ray absorption spectroscopy 9,36,44,45 ) and XPS. 24,32 However, it has also been found that different Ti species in oxidized and reduced form are present after doping.…”

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Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

et al. 2014

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The reversibility of hydrogen sorption in complex hydrides has only been shown unambiguously for NaAlH4 doped with transition metal compounds. Despite a multitude of investigations of the effect of the added catalyst on the hydrogen sorption kinetics of NaAlH4, the mechanism of catalysis remains elusive so far. Following the decomposition of TiCl3-doped NaAlH4 by in-situ X-ray photoelectron spectroscopy (XPS), we link the chemical state of the dopant with those of the hydride and decomposition products. Titanium and aluminium change their oxidation states during cycling. The change of the formal oxidation state of Al from III to zero is partly due to the chemical reaction from NaAlH4 to Al. Furthermore, aluminium oxide is formed (Al2O3), which coexists with titanium oxide (Ti2O3). The interplay of metallic and oxidized Ti with the oxide skin might explain the effectiveness of Ti and similar dopants (Ce, Zr…).

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Complex Hydrides for Energy Storage, Conversion, and Utilization

2019

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functionalities and exhibit great potentials for the applications in the energy transfer chain (Figure 1).In chemistry, a hydride is a compound having negatively charged hydrogen anion. [2] Nowadays, however, hydrogenous compounds having hydrogen bonded to metals or nonmetal in ionic, metallic or covalent manner are collectively referred as hydrides. [3] Complex hydride is such a class of compound having a general formula of M(XH n ) m , where M is usually a metal cation and X is a metal or nonmetal element which sets up covalent or ionocovalent bonding with H. [4] The M[XH n ] m is H-rich and can decompose selectively to H 2 allowing complex hydrides of light-weight elements potential hydrogen storage media. As a matter of fact, since the pioneering work of Ti-catalyzed NaAlH 4 in 1997, [5] extensive investigations on hydrogen storage over alanates, [6] amide-hydride composites, [7] borohydrides, [8] amidoboranes [9] as well as metallorganic hydrides [10] were carried out and tremendous progress has been made (Figure 2). [1,4a] The break and setup of XH bonding would be endergonic and exergonic, respectively. The energy input and output in hydrogen desorption and reabsorption over a complex hydride depends strongly on its thermodynamic stability, which also offers an opportunity of using complex hydrides as thermal energy storage materials to cope up with the intermittent, fluctuating and unstable supply of renewable energies. Owning to their exclusive advantages of diversity, high energy densities and tunability, complex hydrides have been actively pursued for this application since year 2000. [11] Solid electrolytes with fast conduction of Li, Na, or Mg ions are highly demanded for all-solid-state batteries with high energy density and safety. Coincidentally, complex hydrides are composed of those cations and a relatively large sized [XH n ] anion. The coordination flexibility of the large anion with alkali or alkaline earth cation would create some favorable structural features, such as defects and/or low-barrier diffusion channels, to facilitate cation migration within the lattice of complex hydrides. [12] Starting from the finding of high Li-ion conduction in the high-temperature-phase LiBH 4 , [13] a variety of complex hydrides has been developed, some of which show superior ion conductivity to their nonhydride peers. [14] Hydrogen storage over complex hydride would undergo dihydrogen dissociation into surface H atoms followed by H Functional materials are the key enabling factor in the development of clean energy technologies. Materials of particular interest, which are reviewed herein, are a class of hydrogenous compound having the general formula of M(XH n ) m , where M is usually a metal cation and X can be Al, B, C, N, O, transition metal (TM), or a mixture of them, which sets up an iono-covalent or covalent bonding with H. M(XH n ) m is generally termed as a complex hydride by the hydrogen storage community. The rich chemistry between H and B/C/N/O/Al/TM allows complex hydrides of diverse compo...

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Proposed Mechanisms for the Catalytic Activity of Ti in NaAlH₄

Cited by 111 publications

References 193 publications

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

Complex Hydrides for Energy Storage, Conversion, and Utilization

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Proposed Mechanisms for the Catalytic Activity of Ti in NaAlH4

Cited by 111 publications

References 193 publications

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Sodium borohydride hydrazinates: synthesis, crystal structures, and thermal decomposition behavior

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

Complex Hydrides for Energy Storage, Conversion, and Utilization

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Proposed Mechanisms for the Catalytic Activity of Ti in NaAlH₄