Superprotonic Conductivity of MOFs Confining Zwitterionic Sulfamic Acid as Proton Source and Conducting Medium

Abstract

AbstractA few metal–organic frameworks (MOFs), which typically use strong acids as proton sources, display superprotonic conductivity (≈10−1 S cm−1); however, they are rare due to the instability of MOFs in highly acidic conditions. For the first time, we report superprotonic conductivity using a moderately acidic guest, zwitterionic sulfamic acid (HSA), which is encapsulated in MOF‐808 and MIL‐101. HSA acts not only as a proton source but also as a proton‐conducting medium due to its extensive hydrogen bonding ability and zwitterion effect. A new sustained concentration gradient method results in higher HSA encapsulation compared to conventional methods, producing 10HSA@MOF‐808‐(bSA)2 and 8HSA@MIL‐101. These MOFs show impressive superprotonic conductivity of 2.47×10−1 and 3.06×10−1 S cm−1, respectively, at 85 °C and 98 % relative humidity, and maintain stability for 7 days.