Synchrotron X-ray diffraction and X-ray photoelectron spectroscopy studies of NaAlH4 containing Ti–Zr hydride additives

Wan, Chubin; Ju, Xin; Qi, Yingxia; Wang, Shumao; Liu, Xiaopeng; Jiang, Lijun

doi:10.1016/j.jallcom.2009.06.181

Cited by 11 publications

(4 citation statements)

References 22 publications

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“…For instance, the canonical interpretation of the two broad features around 71–72 and 73–76 eV in Figure would assign the lower peaks to the Al 0 oxidation state (Al metal) and the higher peaks to Al 3+ species (Al hydrides and oxides). This interpretation was assumed by Delmelle et al and is widely reported in the literature. ,,, However, Na 3 AlH 6 conflicts with that interpretation since its computed binding energy is close to that of the Al metal. As a result, it should be difficult to distinguish between these two species within the lower-binding-energy feature.…”

Section: Resultsmentioning

confidence: 69%

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Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄

White

Rowberg

Wan

et al. 2019

ACS Appl. Mater. Interfaces

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Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release. In contrast to some previously proposed mechanisms, the titanium dopant does not directly facilitate desorption at the surface. Instead, oxidized surface species, even on well-protected NaAlH 4 samples, evolve during dehydrogenation to form surface hydroxides with differing levels of hydrogen saturation. Additionally, the presence of these oxidized species leads to considerably lower computed barriers for H 2 formation compared to pristine hydride surfaces, suggesting that oxygen may actively participate in hydrogen release, rather than merely inhibiting diffusion as is commonly presumed. These results demonstrate how close experiment−theory feedback can elucidate mechanistic understanding of complex metal hydride chemistry and potentially impactful roles of unavoidable surface impurities.

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Section: Resultsmentioning

confidence: 69%

“…This interpretation was assumed by Delmelle et al and is widely reported in the literature. 30,38,43,44 However, Na 3 AlH 6 conflicts with that interpretation since its computed binding energy is close to that of the Al metal. As a result, it should be difficult to distinguish between these two species within the lowerbinding-energy feature.…”

Section: → + +mentioning

confidence: 99%

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄

White

Rowberg

Wan

et al. 2019

ACS Appl. Mater. Interfaces

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show abstract

“…The Na 3 AlH 6 photoelectron peak in Fig. 13(a-d) for the rehydrogenated samples, located at 64.92 eV, 57 further proves the reformation of Na 3 AlH 6 during the rehydrogenation process. These observations are in accordance with the results of X-ray diffraction, showing that the enhanced rehydriding capacity of the doped sample is induced by the reformation of Na 3 AlH 6 .…”

Section: Resultsmentioning

confidence: 63%

“…This fact is further strengthened by the XPS spectra from the Mg 2p regions of the doped sample (Fig.12b), exhibiting the occurrence of MgO after first dehydrogenation. The Na 3 AlH 6 photoelectron peak in Fig.13(a-d) for the rehydrogenated samples, located at 64.92 eV,57 further proves the reformation of Na 3 AlH 6 during the rehydrogenation process. These observations are in accordance with the results of X-ray diffraction, showing that the enhanced rehydriding capacity of the doped sample is induced by the reformation of Na 3 AlH 6 .The FESEM qualitative and quantitative microstructural investigations have been employed to examine the particle size and morphology of the as-milled and cycled samples.…”

mentioning

confidence: 63%

Enhanced hydrogen storage performance for MgH2–NaAlH4 system—the effects of stoichiometry and Nb2O5 nanoparticles on cycling behaviour

Rafi-Ud-Din

et al. 2012

RSC Adv.

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Nowadays, the technological utilization of reactive hydride composites (RHC) as promising hydrogen storage materials is hampered by their reaction kinetics. In the present work, effects of reactant stoichiometry on ensuing hydrogen sorption properties and pathway of the MgH 2 -NaAlH 4 (mole ratios 1 : 2, 1 : 1 and 2 : 1) system, both undoped and doped with Nb 2 O 5 nanoparticles, were investigated. It was found that the as-prepared reactant stoichiometry of MgH 2 /NaAlH 4 system had a profound impact on its dehydrogenation kinetics and reaction mechanism. Variable temperature dehydrogenation data revealed that undoped binary composites possessed enhanced hydrogen desorption properties compared to that of pristine NaAlH 4 and MgH 2 . The use of Nb 2 O 5 displayed superior catalytic effects in terms of enhancing dehydriding/rehydriding kinetics and reducing the dehydrogenation temperature of MgH 2 -NaAlH 4 system. Isothermal volumetric measurements at 300 uC revealed that enhancements arising upon adding Nb 2 O 5 were almost double that of undoped MgH 2 -NaAlH 4 composites. The apparent activation energies for NaAlH 4 , Na 3 AlH 6 , MgH 2 , and NaH relevant decompositions in doped composite were found to be much lower than that for the undoped one. Moreover, Nb 2 O 5 doping also markedly enhanced the reversible capacity of MgH 2 -NaAlH 4 composites under moderate conditions, persisting well during three de/ rehydrogenation cycles. XRD, XPS, and FESEM-EDS analyses demonstrated that reduction of Nb 2 O 5 during first desorption was coupled to the migration of reduced niobium oxide species from the bulk to the surface of the material. It was suggested that these finely dispersed oxygen-deficient niobium species might contribute to kinetic improvement by serving as the active sites to facilitate hydrogen diffusion through the diffusion barriers both during dehydrogenation and rehydrogenation.

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Valence band of catalyst doped sodium alanate by X-ray photoelectron spectroscopy using synchrotron radiation

Wan

et al. 2010

International Journal of Hydrogen Energy

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Synchrotron X-ray diffraction and X-ray photoelectron spectroscopy studies of NaAlH4 containing Ti–Zr hydride additives

Cited by 11 publications

References 22 publications

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄

Enhanced hydrogen storage performance for MgH2–NaAlH4 system—the effects of stoichiometry and Nb2O5 nanoparticles on cycling behaviour

Valence band of catalyst doped sodium alanate by X-ray photoelectron spectroscopy using synchrotron radiation

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Synchrotron X-ray diffraction and X-ray photoelectron spectroscopy studies of NaAlH4 containing Ti–Zr hydride additives

Cited by 11 publications

References 22 publications

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH4

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH4

Enhanced hydrogen storage performance for MgH2–NaAlH4 system—the effects of stoichiometry and Nb2O5 nanoparticles on cycling behaviour

Valence band of catalyst doped sodium alanate by X-ray photoelectron spectroscopy using synchrotron radiation

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Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH₄