Remarkable proton conducting behavior driven by synergistic effects in acid–base conjugated MOFs impregnated with sulphuric acid molecules

Abstract

The Coulomb force between protons and negative charges usually leads to low proton diffusion and poor proton conductivity. Herein, acid–base conjugated MOFs of UiO-66-SO₃⁻-NH₃⁺ were constructed by linking sulfonic acid and amine groups to an organic skeleton. According to the XPS and elemental analysis, the ratio of 2-aminoterephthalic acid/2-sulfoterephthalic acid was ∼1.9 in UiO-66-SO₃⁻-NH₃⁺. After introducing sulphuric acid molecules, the MOF-based electrolyte exhibited a remarkable proton conductivity of 5.40 × 10⁻¹ S cm⁻¹ and low activation energy of 0.15 eV at 100% RH and 90 °C. This remarkable proton conducting behavior was generated by the synergistic system in the MOF, which contained certain synergistic effects such as between –SO₃⁻⋯H⁺⋯SO₄²⁻ and NH₃⁺⋯SO₄²⁻, therefore possessing a Grotthuss mechanism, which facilitates facile proton transport.