Proton Conduction Study on Water Confined in Channel or Layer Networks of La<sup>III</sup>M<sup>III</sup>(ox)<sub>3</sub>·10H<sub>2</sub>O (M = Cr, Co, Ru, La)

Abstract

Proton conduction of the La<sup>III</sup>M<sup>III</sup> compounds, LaM­(ox)<sub>3</sub>·10H<sub>2</sub>O (abbreviated to <b>LaM</b>; M = Cr, Co, Ru, La; ox<sup>2–</sup> = oxalate) is studied in view of their networks. <b>LaCr</b> and <b>LaCo</b> have a ladder structure, and the ladders are woven to form a channel network. <b>LaRu</b> and <b>LaLa</b> have a honeycomb sheet structure, and the sheets are combined to form a layer network. The occurrence of these structures is explained by the rigidness versus flexibility of [M­(ox)<sub>3</sub>]<sup>3–</sup> in the framework with large La<sup>III</sup>. The channel networks of <b>LaCr</b> and <b>LaCo</b> show a remarkably high proton conductivity, in the range from 1 × 10<sup>–6</sup> to 1 × 10<sup>–5</sup> S cm<sup>–1</sup> over 40–95% relative humidity (RH) at 298 K, whereas the layer networks of <b>LaCr</b> and <b>LaCo</b> show a lower proton conductivity, ∼3 × 10<sup>–8</sup> S cm<sup>–1</sup> (40–95% RH, 298 K). Activation energy measurements demonstrate that the channels filled with water molecules serve as efficient pathways for proton transport. <b>LaCo</b> was gradually converted to La<sup>III</sup>Co<sup>II</sup>(ox)<sub>2.5</sub>·4H<sub>2</sub>O, which had no channel structure and exhibited a low proton conductivity of less than 1 × 10<sup>–10</sup> S cm<sup>–1</sup>. The conduction–network correlation of LaCo­(ox)<sub>2.5</sub>·4H<sub>2</sub>O is reported

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Last time updated on 12/02/2018

This paper was published in FigShare.

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