Proton conductors with wide operating temperature domains achieved by applying a dual-modification strategy to MIL-101

Abstract

Developing an efficient strategy for obtaining proton conductors with wide working temperature domains is of great significance for the wide application of proton conductors. To date, proton conductors that have high proton conductivity from subzero temperatures to high temperatures above 100 °C have been very rare. Herein, we prepared two composites, H₃PO₄@MIL-101-SO₃H(Cr) (1) and H₂SO₄@MIL-101-NH₂(Al) (2) by applying a dual-modification strategy to functionalize MOF MIL-101, that is, incorporating acidic guest molecules into the channels of MIL-101 while modifying the MIL-101 backbone with functional groups. Both composites have high proton conductivity over a broad temperature domain (−40 °C to above 150 °C) due to the complementary conduction or synthetic conduction of the backbone functional group and acidic guest molecules in different temperature ranges. The proton conductivities of 1 are 0.9 × 10⁻¹ S cm⁻¹ at 65 °C and 95% RH, 7.5 × 10⁻⁵ S cm⁻¹ at −40 °C and 1.4 × 10⁻² S cm⁻¹ at 150 °C. Further, the proton conductivities of 2 are 5.8 × 10⁻² S cm⁻¹ at 65 °C and 95% RH, 7.1 × 10⁻⁴ S cm⁻¹ at −40 °C and 2.5 × 10⁻⁴ S cm⁻¹ at 170 °C. All the proton conductivities of the two composites in three temperature domains (low, moderate and high temperature) are at a high level among those of reported proton conductors. Moreover, their proton conductivities have good stability and durability in the broad temperature region from subzero temperatures to high temperatures above 100 °C.