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Effect of Elevated Temperatures on the States of Water and Their Correlation with the Proton Conductivity of Nafion
ACS Omega ( IF 3.7 ) Pub Date : 2018-01-11 00:00:00 , DOI: 10.1021/acsomega.7b01765 Mohammad A Barique 1 , Eiji Tsuchida 2 , Akihiro Ohira 1, 3 , Kohji Tashiro 4
ACS Omega ( IF 3.7 ) Pub Date : 2018-01-11 00:00:00 , DOI: 10.1021/acsomega.7b01765 Mohammad A Barique 1 , Eiji Tsuchida 2 , Akihiro Ohira 1, 3 , Kohji Tashiro 4
Affiliation
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For the first time, we report the effects of elevated temperatures, from 80 to 100 °C, on the changes in the states of water and ion–water channels and their correlation with the proton conductivity of Nafion NR212, which was investigated using a Fourier transform infrared spectroscopy study. Experimentally, three types of water aggregates, protonated water (H+(H2O)n), nonprotonated hydrogen (H)-bonded water (H2O···H2O), and non-H-bonded water, were found in Nafion, and the existence of those three types of water was confirmed through ab initio molecular dynamics simulation. We found that the proton conductivity of Nafion increased for up to 80 °C, but from 80 to 100 °C, the conductivity did not increase; rather, all of those elevated temperatures showed identical conductivity values. The proton conductivities at lower relative humidities (RHs) (up to 50%) remained nearly identical for all elevated temperatures (80, 90, and 100 °C); however, from 60% RH (over λ = 4), the conductivity remarkably jumped for all elevated temperatures. The results indicated that the amount of randomly arranged water gradually increased and created more H-bonded water networks in Nafion at above 60% RH. From the deconvolution of the O–H bending band, it was found that the volume fraction fi (i=each deconvoluted band) of H-bonded water for elevated temperatures (>80–100 °C) increased remarkably higher than for 60 °C.
中文翻译：
升高温度对水状态的影响及其与 Nafion 质子电导率的相关性
我们首次报告了 80 至 100 °C 高温对水和离子水通道状态变化的影响及其与 Nafion NR212 质子电导率的相关性，并使用傅立叶研究了这一点变换红外光谱研究。实验中，制备了三种类型的水聚集体：质子化水(H + (H 2 O) n )、非质子化氢(H)键水(H 2 O…H 2 O)和非H键水。在 Nafion 中发现了这种水，并且通过从头算分子动力学模拟证实了这三种水的存在。我们发现Nafion的质子电导率在高达80℃时有所增加，但从80℃到100℃，电导率没有增加；相反，所有这些升高的温度都显示出相同的电导率值。在较低相对湿度 (RH)（高达 50%）下，质子电导率在所有高温（80、90 和 100 °C）下几乎保持不变；然而，从 60% RH（超过 λ = 4）开始，所有高温下的电导率均显着跃升。结果表明，在 60% RH 以上时，Nafion 中随机排列的水量逐渐增加，并形成更多的氢键水网络。从O-H弯曲带的反褶积中发现，在高温（>80-100°C）下，H键水的体积分数fi （ i =每个反褶积带）显着高于60° C.
更新日期：2018-01-11
中文翻译：
升高温度对水状态的影响及其与 Nafion 质子电导率的相关性
我们首次报告了 80 至 100 °C 高温对水和离子水通道状态变化的影响及其与 Nafion NR212 质子电导率的相关性，并使用傅立叶研究了这一点变换红外光谱研究。实验中，制备了三种类型的水聚集体：质子化水(H + (H 2 O) n )、非质子化氢(H)键水(H 2 O…H 2 O)和非H键水。在 Nafion 中发现了这种水，并且通过从头算分子动力学模拟证实了这三种水的存在。我们发现Nafion的质子电导率在高达80℃时有所增加，但从80℃到100℃，电导率没有增加；相反，所有这些升高的温度都显示出相同的电导率值。在较低相对湿度 (RH)（高达 50%）下，质子电导率在所有高温（80、90 和 100 °C）下几乎保持不变；然而，从 60% RH（超过 λ = 4）开始，所有高温下的电导率均显着跃升。结果表明，在 60% RH 以上时，Nafion 中随机排列的水量逐渐增加，并形成更多的氢键水网络。从O-H弯曲带的反褶积中发现，在高温（>80-100°C）下，H键水的体积分数fi （ i =每个反褶积带）显着高于60° C.
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