• Milla-Pérez, Diego F.
• Durán-Martín, Jonatan D.
• Rius, Jordi
• Demadis, Konstantinos D.
• Olivera-Pastor, Pascual
• Cabeza, Aurelio
• Aranda, Miguel A. G.
• Losilla, Enrique R.
• Moreno-Real, Laureano
• Bazaga-García, Montse
• Salcedo, Inés R.
• Colodrero, Rosario M. P.

Abstract

<jats:title>Abstract</jats:title><jats:p>The structural variability of two series of Mg<jats:sup>2+</jats:sup>- and Zn<jats:sup>2+</jats:sup>- 2-hydroxyphosphonoacetates have been studied in the range of 25–80°C and 95% relative humidity in order to correlate the structure with the proton conductivity properties. In addition to selected previously reported 1D, 2D and 3D materials, a new compound, KZn<jats:sub>6</jats:sub>(OOCCH(OH)PO<jats:sub>3</jats:sub>)<jats:sub>4</jats:sub>(OH)·5H<jats:sub>2</jats:sub>O (KZn<jats:sub>6</jats:sub>-HPAA-3D), has been prepared and thoroughly characterized. The crystal structure of this solid, solved ab initio from synchrotron X-ray powder diffraction data, consists of a negatively charged 3D framework with K<jats:sup>+</jats:sup> ions, as compensating counterions. It also contains water molecules filling the cavities in contrast to the potassium-free 3D anhydrous NH<jats:sub>4</jats:sub>Zn(OOCCH(OH)PO<jats:sub>3</jats:sub>) (NH<jats:sub>4</jats:sub>Zn-HPAA-3D). In the range of temperature studied, the 1D materials exhibit a 1D→2D solid-state transition. At 80°C and 95% RH, the 2D solids show moderate proton conductivities, between 2.1×10<jats:sup>−5</jats:sup> S·cm<jats:sup>−1</jats:sup> and 6.7×10<jats:sup>−5</jats:sup> S·cm<jats:sup>−1</jats:sup>. The proton conductivity is slightly increased by ammonia adsorption up to 2.6×10<jats:sup>−4</jats:sup> S·cm<jats:sup>−1</jats:sup>, although no ammonia intercalation was observed. As synthesized KZn<jats:sub>6</jats:sub>-HPAA-3D exhibits a low proton conductivity, 1.6×10<jats:sup>−6</jats:sup> S·cm<jats:sup>−1</jats:sup>, attributed to the basic character of the framework and a low mobility of water molecules. However, this solid transforms to the 2D phase, Zn(OOCCH(OH)PO<jats:sub>3</jats:sub>H)·2H<jats:sub>2</jats:sub>O, upon exposure to dry HCl(g), which enhances the proton conductivity with respect to the as-synthesized 2D material (4.5×10<jats:sup>−4</jats:sup> S·cm<jats:sup>−1</jats:sup>). On the other hand, NH<jats:sub>4</jats:sub>Zn-HPAA-3D exhibited a higher proton conductivity, 1.4×10<jats:sup>−4</jats:sup> S·cm<jats:sup>−1</jats:sup>, than the K<jats:sup>+</jats:sup> analog.</jats:p>

Topics

• impedance spectroscopy
• compound
• phase
• mobility
• Potassium