期刊
ACS APPLIED MATERIALS & INTERFACES
卷 11, 期 14, 页码 13423-13432出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.9b01121
关键词
MOF; post-synthetic modification; superproton conductors; humidity-assisted proton conduction; effect of chain length
资金
- SERB, DST, Government of India [EMR/2017/002971]
- DST INSPIRE, New Delhi
- DSKPDF Scheme, UGC, New Delhi
- UGC-BSR
- UGC
- UGC Government of India, New Delhi
Metal organic framework (MOF) based proton conductors have received immense importance recently. The present study endeavors to design two post synthetically modified UiO-66-based MOFs and examines the effects of their structural differences on their proton conductivity. UiO-66-NH2 is modified by reaction with sultones to prepare two homologous compounds, that is, PSM 1 and PSM 2, with SO3H functionalization in comparable extent (Zr:S = 2:1) in both. However, the pendant alkyl chain holding the -SO3H group is of different length. PSM 2 has longer alkyl chain attachment than PSM 1. This difference in the length of side arms results in a huge difference in proton conductivity of the two compounds. PSM 1 is observed to have the highest MOF-based proton conductivity (1.64 X 10(-1) S cm(-1)) at 80 degrees C, which is comparable to commercially available Nafion, while PSM 2 shows significantly lower conductivity (4.6 X 10(-3) S cm(-1)). Again, the activation energy for proton conduction is one of the lowest among all MOF-based proton conductors in the case of PSM 1, while PSM 2 requires larger activation energy (almost 3 times). This profound effect of variation of the chain length of the side arm by one carbon atom in the case of PSM 1 and PSM 2 was rather surprising and never documented before. This effect of the length of the side arm can be very useful to understand the proton conduction mechanism of MOF-based compounds and also to design better proton conductors. Besides, PSM 1 showed proton conductivity as high as 1.64 x 10(-1) S cm(-1) at 80 degrees C, which is the highest reported value to date among all MOF-based systems. The lability of the SO3H proton of the post synthetically modified UiO-66 MOFs has theoretically been determined by molecular electrostatic potential analysis and theoretical pK(a) calculation of models of functional sites along with relevant NBO analyses.
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