Proton conductivity of Al(H2PO4)3-H3PO4 composites at intermediate temperature

Xiaoxiang Xu, Shanwen Tao, J. T S Irvine

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20 Citations (Scopus)


Composites of Al(H2PO4)3 and H3PO4 were synthesised by soft chemical methods with different Al/P ratios. The Al(H2PO4)3 obtained was found to have a hexagonal symmetry with parameter a = 13.687(3)Å, c = 9.1328(1)Å. The conductivity of this material was measured by a.c. impedance spectroscopy between 100 °C and 200 °C in different atmospheres. The conductivity of pure Al(H2PO4)3 in air is in the order of 10- 6-10- 7 S/cm between 100 and 200 °C. For samples containing small excess of H3PO4, much higher conductivity was observed. The impedance responses of the composites were found to be similar with AlH2P3O10·nH2O under different relative humidity. The conductivity of Al(H2PO4)3-H3PO4 composite with Al/P = 1/3.5 reached 6.6 mS/cm at 200 °C in wet 5% H2. The extra acid is found to play a key role in enhancing the conductivity of Al(H2PO4)3-H3PO4 composite at the surface region of the Al(H2PO4)3 in a core shell type behaviour. 0.7% excess of H3PO4 can increase the conductivity by three orders of magnitude. These composites might be alternative electrolytes for intermediate temperature fuel cells and other electrochemical devices. Conductivity (9.5 mS/cm) changed little, when the sample was held at 175 °C for over 100 h as the conductivity stabilised. © 2008 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)343-350
Number of pages8
JournalSolid State Ionics
Issue number4-5
Publication statusPublished - 27 Apr 2009


  • A.c. impedance spectroscopy
  • Al(H 2 PO 4 ) 3
  • Phosphoric acid
  • Proton conductivity


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