Ultrafast Bulk Diffusion of AlHx in High-Entropy Dehydrogenation Intermediates of NaAlH4

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• 作者：Feng Zhang ; Brandon C. Wood ; Yan Wang ; Cai-Zhuang Wang ; Kai-Ming Ho ; Mei-Yin Chou
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：August 14, 2014
• 年：2014
• 卷：118
• 期：32
• 页码：18356-18361
• 全文大小：320K
• ISSN：1932-7455

文摘

Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in 纬-NaAlH₄, a recently proposed high-entropy polymorph of NaAlH₄. For charged AlH₄^{鈥?/sup> and neutral AlH₃ vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the 伪 phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of 纬-NaAlH₄, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the 伪 phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH₄. Our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH₄ are discussed.}