Proton Conductivities in Functionalized UiO-66: Tuned Properties, Thermogravimetry Mass, and Molecular Simulation Analyses

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• 作者：Fan Yang ; Hongliang Huang ; Xiayan Wang ; Fan Li ; Yuhan Gong ; Chongli Zhong ; Jian-Rong Li
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：December 2, 2015
• 年：2015
• 卷：15
• 期：12
• 页码：5827-5833
• 全文大小：437K
• ISSN：1528-7505

文摘

Pursuing new proton-conducting materials has become a key issue to improve the performance of proton exchange membrane fuel cells for clean energy. As newly emerging materials, metal鈥搊rganic frameworks (MOFs) have been attracting wide attention in this regard. Herein, using stable UiO-66 as a platform, through the modification of different functional groups of 鈭扴O₃H, 鈭?COOH, 鈭扤H₂, and 鈭払r in ligands, we explore the strategy to tune the proton conductivities of MOFs. With the highly acidic and strong hydrophilic functional groups 鈭扴O₃H and 鈭扖OOH, UiO-66-SO₃H and UiO-66-2COOH show quite high proton conductivities of 0.34 脳 10^鈥? and 0.10 脳 10^鈥? S cm^鈥? at 303 K and 鈭?7% relative humidity, respectively while the 鈭扤H₂, 鈭扝, and 鈭払r represent comparatively low conductivities under the same conditions. Furthermore, water molecules adsorbed in the pores are proved to contribute greatly to the proton conductivities of these MOFs. Thermogravimetry-mass spectrometry (TG-MS) and molecular simulations are then used to analyze the interactions between the water molecules and MOFs. TG-MS analyses show two water molecule loss processes in UiO-66-SO₃H and UiO-66-2COOH, but one in UiO-66-NH₂, UiO-66, and UiO-66-Br during heating, which indicates the stronger affinity of 鈭扴O₃H and 鈭扖OOH functionalized UiO-66 toward water molecules than those with 鈭扤H₂ and 鈭払r, as well as UiO-66 itself. The isosteric heats (鈭?i>Q_st) of water adsorption and radial distribution functions (RDFs) in these MOFs are also evaluated by molecular simulations. It was found that UiO-66-SO₃H and UiO-66-2COOH have higher 鈭?i>Q_st of 86.50 and 52.10 kJ mol^鈥?, whereas UiO-66-NH₂, UiO-66, and UiO-66-Br have lower ones, 34.03, 19.04, and 36.36 kJ mol^鈥?, respectively. The RDFs reveal the formation of hydrogen-bonding networks in UiO-66-SO₃H, UiO-66-2COOH, UiO-66-NH₂, and UiO-66, but not in UiO-66-Br.