Superprotonic Conductivity of MOF-808 Achieved by Controlling the Binding Mode of Grafted Sulfamate

Abstract

A metal-organic framework (MOF) having superprotonic conductivity, MOF-808, is prepared by modulating the binding mode of the sulfamate (SA) moieties grafted onto the metal clusters. The activation of the SA-grafted MOF-808 at 150 degrees C changes the binding mode of the grafted SA from monodentate to bridging bidentate, thus converting the neutral amido (-S-NH2) moiety of the grafted SA to the more acidic cationic sulfiliminium (-S=NH2+) moiety. Further, the acidic sulfiliminium moiety of MOF-808-4SA-150 results in more efficient proton conduction than the amido moiety of MOF-808-4SA-60. At 60 degrees C and 95 % relative humidity, MOF-808-4SA-150 is found to have a proton conductivity of 7.89x10(-2) S cm(-1), which is more than 30-times higher than that of MOF-808-4SA-60. Moreover, this superprotonic conductivity is well maintained over 1000 cycles of conductivity measurements and for similar cyclic measurements each day for seven days.