Incorporation of polyoxometalate-based acid–base pair into a sulfonated MIL-101 for achieving proton-conduction materials with high proton conductivity and high stability

Currently, it is of great significance to develop new proton-conduction materials with high proton conductivity, high stability, and good conducting durability to meet the demands of fuel cell and sensors. Herein, we prepared two composites DETA-HPW@MIL-101-SO3H 1 and TETA-HPW@MIL-101-SO3H 2 (DETA = diethylenetriamine, HPW = H3PW12O40·xH2O, MIL = Material Institut Lavoisier, TETA = triethylenetetramine) by encapsulating polyoxometalate (POM) and organic amine into a sulfonated MIL-101 through a step-by-step dipping method. Delightedly, 1 and 2 have high proton conductivities of 6.4 × 10−2 and 2.9 × 10−2 S·cm−1 at 65 °C and 95% relative humidity (RH), respectively, which can be attributed to the fast proton transfer among acid–base pairs formed between HPW and organic amine as well between sulfonic acid and organic amine. Moreover, the time-dependent test in proton conductivity displays that their proton-conduction properties have good stability and durability, which benefit from that the electrostatic interactions among acid–base pairs and the limitation of opening size of MIL-101-SO3H make HPW and organic amine stably exist in the cages of MIL-101-SO3H. The remarkable proton-conduction properties (high proton conductivity and high stability) of the two composites make them become promising proton-conduction materials.