Issue 16, 2009

Phosphonic acid functionalized silicas for intermediate temperature proton conduction

Abstract

Highly proton conductive silicas with phosphonic acid functionalization were synthesized by co-condensation of diethylphosphatoethyltriethoxysilane (DPTS) and tetraethoxysilane in a sol-gel process, followed by acidification of the phosphonate groups. These functionalized silicas with various phosphonic acid contents were extensively characterized to examine their structures and properties; in particular their intermediate temperature proton conductivity at 100–150 °C were systematically investigated under a variety of relative humidity (RH) conditions. The prepared samples have a mesoporous or nonporous structure depending on the DPTS amount used in the synthesis, and show high thermal stability under inert and oxidative atmospheres. We found that the present silicas still exhibit water-dependent proton conduction, but their conductivity under low humidity conditions has been significantly enhanced by up to two orders of magnitude compared to those phosphonic acid functionalized silicas previously reported. Herein, the highest conductivity has been obtained at 150 °C ranging from 4.4 × 10−4 S cm−1 at 20% RH to 0.031 S cm−1 at 100% RH. In general, proton conductivity is largely influenced by the content of phosphonic acid and the porous structure of the materials. Notably, the uniform mesostructure with a high surface area was found to greatly improve the proton conductivity at low humidity. The vehicle mechanism dominates the proton conduction at high humidity, whereas the conductivity at low humidity is likely a consequence of the structure diffusion (the Grotthuss mechanism). In addition, these materials are insoluble in water, rendering a practical suitability for fuel cell applications.

Graphical abstract: Phosphonic acid functionalized silicas for intermediate temperature proton conduction

Supplementary files

Article information

Article type
Paper
Submitted
31 Oct 2008
Accepted
26 Jan 2009
First published
23 Feb 2009

J. Mater. Chem., 2009,19, 2363-2372

Phosphonic acid functionalized silicas for intermediate temperature proton conduction

Y. G. Jin, S. Z. Qiao, Z. P. Xu, Z. Yan, Y. Huang, J. C. Diniz da Costa and G. Q. Lu, J. Mater. Chem., 2009, 19, 2363 DOI: 10.1039/B819379G

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