Proton Conductivity in Doped Aluminum Phosphonate Sponges. Issue 4 (26th February 2014)

• Record Type: Journal Article
• Authors: Wegener, Jennifer; Kaltbeitzel, Anke; Graf, Robert; Klapper, Markus; Müllen, Klaus
• Is Part Of: ChemSusChem. Volume 7:Issue 4(2014:Apr.)
• Page Start: 1148
• Page End: 1154
• Publication Date: 2014-02-26
• Subjects: Green chemistry -- Periodicals; Sustainable engineering -- Periodicals; Chemistry -- Periodicals; Chemical engineering -- Periodicals; 660
• DOI: 10.1002/cssc.201301055
• Languages: English
• ISSNs: 1864-5631

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Proton‐conducting networks (NETs) were prepared successfully by the insertion of phosphonated nanochannels into organic–inorganic hybrid materials that contain Al³⁺ as the connector and hexakis(<italic>p</italic>‐phosphonatophenyl)benzene (HPB) as the linker. Noncomplexed phosphonic acid groups remain in the framework, which depends on the ratio of both compounds, to yield a proton conductivity in the region of 10⁻³ S cm⁻¹. This conductivity can be further improved and values as high as Nafion, a benchmark proton‐exchange membrane for fuel cell applications, can be obtained by filling the network pores with intrinsic proton conductors. As a result of their sponge‐like morphology, aluminum phosphonates adsorb conductive small molecules such as phosphonic acids, which results in a very high proton conductivity of approximately 5×10⁻² S cm⁻¹ at 120 °C and 50 % relative humidity (RH). Contrary to Nafion, the doped networks show a remarkably low temperature dependence of proton conductivity from external humidification. This effect indicates a transport mechanism that is different to the water vehicle mechanism. Furthermore, the materials exhibit an activation energy of 40 kJ mol⁻¹ at 15 % RH that starts to diminish to 10 kJ mol⁻¹ at 80 % RH, which is even smaller than the corresponding values obtained for Nafion 117.</p> </abstract>