Ionization of a neutral MOF to disperse and anchor acid for boosting anhydrous proton conductivity

Abstract

Although incorporation of proton conducting molecules (PCMs) is one of the most effective methods to enhance the anhydrous conductivity, most materials including MOFs are challenged by the leakage and poor dispersion of PCMs, severely decreasing the anhydrous proton conductivity. Herein, we propose a neutral framework ionization strategy to construct positive and negative charge centers for dispersing and anchoring the encapsulated PCMs. The N+ and –SO3– sites in MOF-867-PS are thus constructed through modifying MOF-867 with 1,3-propane sultone (PS). After incorporating trifluoromethanesulfonic acid (CF3SO3H, TFOH) the resultant MOF-867-PS-XTFOH (X is volume of TFOH/μL per 100 mg MOFs) composites disperse and anchor the CF3SO3− and H+ ions through electrostatic interaction to form smooth proton transport pathway, benefiting to the high proton conductivity. Especially, MOF-867-PS-100TFOH exhibits sharply enhanced proton conductivity over 10−3 S cm−1, almost two orders of magnitude higher than pristine MOF-867 loaded with equimolar acid and comparable to the top-ranking anhydrous proton conducting MOF composites. This work is the first post–synthetic modification in MOFs to assemble multiple sites for anchoring the functional molecules, opening an effective path to fabricate the high–performance MOFs for proton conduction or other functionalities.