Protonic Conductivity of Nanocrystalline Zeolitic Imidazolate Framework 8
Protonic Conductivity of Nanocrystalline Zeolitic Imidazolate Framework 8
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DOI：
10.1016/j.electacta.2014.11.093
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发表时间：
2015-01-20
影响因子：
6.6
通讯作者：
Figueiredo, Filipe M. L.
中科院分区：
文献类型：
--
作者：
Barbosa, Paula;Rosero-Navarro, Nataly C.;Figueiredo, Filipe M. L.
在寻找新型质子导体的过程中，描述了通过胶体化学途径由硝酸锌和 2-甲基咪唑 (Hmim) 合成和表征沸石咪唑骨架 8 (ZIF8) 纳米晶体。 ZIF8粉末具有方钠石立方结构，晶胞参数略超过1.7 nm，微晶尺寸在30至50 nm之间，比表面积在800至2251 m(2)g(-1)之间，与高水平的微孔率和中孔的一些贡献有关。在 98% 相对湿度 (RH) 下收集的 ZIF8 粉末压块的阻抗谱描述了至少 3 个贡献，这可归因于高频时的体电阻以及中频和低频时的外部界面现象。从这些数据中提取的电导率数据显示出很强的湿度依赖性，在 94 摄氏度时，相对湿度在 20% 到 98% 之间增加了 4 个数量级以上，这归因于质子沿着吸附的水分子传输。具有最高表面积的样品的电导率提高了 1 个数量级，在 94 摄氏度和 98% 相对湿度下达到最大 4.6 x 10(-4) Scm(-1)，这也证明了这一点。该值较低，但与报道的这些材料的低吸水能力一致。令人惊讶的是，传导的活化能高达110 kJmol(-1)，这可能表明该结构对质子扩散的特殊影响。虽然传输特性对于任何技术应用来说仍然不足，但这些初步结果证明了 ZIF8 结构的潜力，将卓越的热稳定性和水解稳定性与通过适当的功能化轻松引入高水平质子传输的潜力结合起来。 (C) 2014 Elsevier Ltd. 保留所有权利。
The synthesis and characterization of nanocrystals of the zeolitic imidazolate framework-8 (ZIF8) from zinc nitrate and 2-methylimidazole (Hmim) by a colloidal chemistry route is described in the search for novel protonic conductors. The ZIF8 powders have the sodalite cubic structure with a unit cell parameter slightly in excess of 1.7 nm, a crystallite size between 30 and 50 nm, and specific surface area between 800 and 2251 m(2)g(-1), associated to high levels of microporosity and some contribution of mesopores. The impedance spectra of ZIF8 powder compacts collected under 98% relative humidity (RH) depict at least 3 contributions, which could be ascribed to the bulk resistance at high frequency, and to external interfacial phenomena at intermediate and low frequencies. The conductivity data extracted from these data display strong humidity dependence, increasing by more than 4 orders of magnitude between 20 and 98% RH at 94 degrees C, ascribed to proton transport along adsorbed water molecules. This is also supported by the enhancement of 1 order of magnitude of the conductivity of samples with highest surface area, attaining a maximum of 4.6 x 10(-4) Scm(-1) at 94 degrees C and 98% RH. The value is low, but in agreement with the reported low water uptake capacity of these materials. Surprisingly, the activation energy for conduction is as high as 110 kJmol(-1), which may denote a particular influence of the structure on proton diffusion. While the transport properties are still short for any technological application, these first results demonstrate the potential of the ZIF8 structure to combine exceptional thermal and hydrolytic stability with the potential to easily introduce high levels of proton transport by suitable functionalization. (C) 2014 Elsevier Ltd. All rights reserved.