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

A porous metal–organic framework (MOF), [Ni 2 (dobdc)(H 2 O) 2 ]⋅6 H 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 2.2×10 −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 + @Ni 2 (dobdc) play an important role in the conduction process.