Phase Behavior and Superprotonic Conductivity in the System (1– x )CsH 2 PO 4 – x H 3 PO 4 : Discovery of Off-Stoichiometric α-[Cs 1–x H x ]H 2 PO 4
Phase Behavior and Superprotonic Conductivity in the System (1– x )CsH 2 PO 4 – x H 3 PO 4 : Discovery of Off-Stoichiometric α-[Cs 1–x H x ]H 2 PO 4
复制标题
系统中的相行为和超质子电导率 (1–x )CsH 2 PO 4 – x H 3 PO 4 ：非化学计量α-[Cs 1–x H x ]H 2 PO 4 的发现
DOI：
10.1021/acs.chemmater.1c04061
复制
发表时间：
2022
影响因子：
8.6
通讯作者：
Haile, Sossina M.
中科院分区：
文献类型：
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作者：
Wang, Louis S.;Patel, Sawankumar V.;Truong, Erica;Hu, Yan-Yan;Haile, Sossina M.
CsH_2PO_4由于其在中温(228-300°C)下具有高度无序的立方结构的特殊导电性而作为质子导电电解液引起了人们的兴趣。本文通过对CsH_2PO_4(CDP)和CsH_5(PO_4)_2混合物的研究，发现立方相形成了组成[Cs1-xHx]H_2PO_4的固溶体，x至少可延伸到2/9。通过热分析、高温X射线衍射实验和变温核磁共振光谱绘制了组成空间(1-x)Cs_2PO_4-xH_3PO_4，0≤x≤_2/9的相图。当温度高于90℃时，化学计量比的CDP与Cs7(H4PO4)(HPO4)8处于平衡状态。这两个相呈现共析行为，其共析反应温度和组成分别为155℃和x=0.18，生成立方体[CS1-xHx]HPO4。结构研究表明，相当显著的是，立方相容纳了阳离子中心上的空位，这些空位被过剩的质子电荷平衡，后者与磷酸基团在化学上相关。用阻抗谱测量了不同组成的立方相的电导率，与CDP的电导率相当。在远低于化学计量比CDP的超质子转变温度下，非化学计量比立方体[CS1-xHx]H_2PO_4具有优异的质子导电性，这为延长基于CDP的器件的低温工作极限提供了机会。更广泛地说，这里展示的非化学计量相行为为超质子固体酸化合物的修饰引入了一种新的方法。
CsH2PO4has garnered interest as a proton-conducting electrolyte due to its exceptional conductivity at intermediate temperatures (228–300 °C) at which it adopts a cubic structure with a high degree of disorder. Here, through a study of mixtures of CsH2PO4(CDP) and CsH5(PO4)2, the cubic phase was discovered to form solid solutions of composition [Cs1–xHx]H2PO4, withxextending to at least 2/9. A phase diagram of the composition space (1–x)CsH2PO4–xH3PO4, 0 ≤x≤ 2/9 was developed through thermal analysis, high-temperature in situ X-ray diffraction experiments, and variable-temperature NMR spectroscopy. At temperatures above about 90 °C, monoclinic, stoichiometric CDP exists in equilibrium with Cs7(H4PO4)(H2PO4)8. These two phases displayed eutectoid behavior, with a eutectoid reaction temperature and composition of 155 °C andx= 0.18, respectively, to form cubic [Cs1–xHx]H2PO4. The structural studies revealed, rather remarkably, that the cubic phase accommodates vacancies on the cation site that are charge-balanced by excess protons, where the latter are chemically associated with phosphate groups. The conductivities of cubic phases of various compositions, measured by impedance spectroscopy, are comparable to that of CDP. The excellent proton conductivities of off-stoichiometric, cubic [Cs1–xHx]H2PO4at temperatures well below the superprotonic transition of stoichiometric CDP present the opportunity to extend the low-temperature operating limit of CDP-based devices. More generally, the off-stoichiometric phase behavior demonstrated here introduces a new approach for the modification of superprotonic solid acid compounds.