Chemical Diffusivity for Hydrogen Storage: Pneumatochemical Intermittent Titration Technique

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• 作者：Young-Hun Kim ; Eui-Chol Shin ; Sun-Jung Kim ; Choong-Nyeon Park ; Jaekook Kim ; Jong-Sook Lee
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 3, 2013
• 年：2013
• 卷：117
• 期：39
• 页码：19771-19785
• 全文大小：968K
• 年卷期：v.117,no.39(October 3, 2013)
• ISSN：1932-7455

文摘

Point relaxations for the pressure鈥揷omposition isotherms were analyzed as a solid-state diffusion problem of hydrogen solutes from the gas phase provided in a limited amount by a pulse-like supply. For the large differential hydrogen storage, typical in the PCI plateau region, represented by small effective volume ratio 位 parameter in the diffusion equation, the relaxation occurs much faster than in the galvanostatic or potentiostatic relaxations for the same chemical diffusivity values. The analysis was successfully applied to Mg/MgH₂ system and the apparent chemical diffusivity and the hydrogen self-diffusivity were evaluated as a function of the state of hydrogen storage, in an analogous manner to the well-known electrochemical titration techniques. The increase in the apparent chemical diffusivity and hydrogen self-diffusivity in the plateau region with the increasing state of storage can be consistently explained by the lower hydrogen self-diffusivity in MgH₂ than in Mg solid solution. The hydrogen self-diffusivity variation in the single phase MgH₂ region suggests the vacancy mechanism. The method is named as pneumatochemical intermittent titration technique (PnITT).