High ionic conductivity of Mg-Al layered double hydroxides at intermediate temperature (100-200°C) under saturated humidity condition (100% RH)

Hag Soo Kim, Yohtaro Yamazaki, Je Deok Kim, Tetsuichi Kudo, Itaru Homma

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Ionic conduction properties of layered double hydroxides (LDHs), [Mg (1-x)Al(x)(OH)2](CO3) x/2-nH2O (=CO3-type) and [Mg (1-x)Al(x)(OH)2](OH)x-nH 2O(=OH-type), have been investigated in the temperature range of 25-200 °C under saturated water vapor pressure (100% RH). Conductivity was measured by the complex impedance method using pressed pellet samples. The conductivity of an OH-type sample (x = 0.25) is as high as 4×10 -3 Scm-1 already at room temperature. On heating, it increases as slowly (the activation energy Ea∼ 55 meV) as those of liquid electrolyte solutions, suggesting that ions are transported via exchange of protons between OH- and H2O species in the interlayer space of the LDH (a kind of the Grotthus mechanism). The conductivity at 200 °C reaches 3×10-2Scm-1.Althoughthe conductivity of the CO3-type counterpart is considerably low (∼10-6 Scm-1) at room temperature, it increases with increasing temperature with showing a jump by about four orders of magnitude around 80°C, after which the compound is turned into an almost the same liquid-like conductor as the OH-type sample; the conductivity jump is probably due to the interlayer reaction CO2- 3 + H 2O=2OH- + CO2 (g). Thus those Mg-Al LDH materials show the potential application as solid electrolyte materials for intermediate temperature fuel cells, not only because they have high conductivity but also they should not suffer from the degradation by CO 2 which is a serious problem for conventional anion exchange membranes.

Original languageEnglish
Pages (from-to)883-888
Number of pages6
JournalSolid State Ionics
Volume181
Issue number19-20
DOIs
Publication statusPublished - 2010 Jul 16
Externally publishedYes

Keywords

  • AEMFC
  • Electrolytes
  • Ionic conduction
  • LDHs

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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