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pH-Dependent Proton Conducting Behavior in a Metal–Organic Framework Material

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  • This work was supported by a Korea CCS R&D Center (KCRC) grant funded by the Korean government (The Ministry of Science, ICT & Future Planning (MSIP)) (NRF-2013M1A8A1035849).

Abstract

A porous metal–organic framework (MOF), [Ni2(dobdc)(H2O)2]⋅6 H2O (Ni2(dobdc) or Ni-MOF-74; dobdc4−=2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H+@Ni2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2×10−2 S cm−1 at 80 °C and 95 % relative humidity (RH), approaching the highest values reported for MOFs. Proton conduction occurs via the Grotthuss mechanism with a significantly low activation energy as compared to other proton-conducting MOFs. Protonated water clusters within the pores of H+@Ni2(dobdc) play an important role in the conduction process.

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