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

Abstract

A porous metal-organic framework (MOF), [Ni-2-(dobdc)(H2O)2]center dot 6H(2)O (Ni-2(dobdc) or Ni-MOF-74; dobdc(4) = 2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni-2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H@Ni-2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2 x 10(-2) S cm(-1) at 80 degrees 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@Ni-2(dobdc) play an important role in the conduction process.