Effect of hydrogen-bonding networks in water on the proton conductivity properties of metal–organic frameworks

Abstract

We study the proton conductivity properties of MOF-801. We find that MOF-801 possesses intrinsic proton carrier sites, m3-OH groups, in clusters yielding the generation of hydrogen-bonding networks with guest water molecules at high relative humidity (RH), facilitating proton transport. Remarkably, this material has a high proton conductivity of 1.82 10 3 S cm 1 under 98% RH at 90 C and maintains its performance over an extended time. Our investigations reveal that the increase in proton conductivity is correlated to numerous hydrogen bonds within the MOF structure. The activation energy of this process is low (Ea ¼ 0.21 eV), showing that the protons hop through the membrane by the Grotthus mechanism. Interestingly, density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations show that a water cluster mechanism dominates the proton conductivity in this material via the large number of hydrogen bonds formed at different temperatures and relative humilities.