A Water Stable Magnesium MOF That Conducts Protons over 10^–2 S cm^–1

Abstract

From the outset of the study of MOFs as proton conductors, both conductivity and hydrolytic robustness of the materials have needed to be improved. Here, we report a layered magnesium carboxyphosphonate framework, PCMOF10, that shows an extremely high proton conductivity value of 3.55 × 10(-2) S·cm(-1) at 70 °C and 95% RH. Moreover, PCMOF10 is water stable owing to strong Mg phosphonate bonding. The 2,5-dicarboxy-1,4-benzenediphosphonic acid (H6L) linker anchors a robust backbone and has hydrogen phosphonate groups that interact with the lattice water to form an efficient proton transfer pathway.

Metal–Organic Frameworks and Other Crystalline Materials for Ultrahigh Superprotonic Conductivities of 10−2 S cm−1 or Higher

“…A dicarboxy‐diphosphonate ligand was applied for constructing highly water‐stable MOF Mg 2 (H 2 O) 4 (H 2 L 1 )H 2 O (PCMOF‐10) through the use of both carboxylate and phosphonate acid groups onto a single ligand (H 2 L 1 ) . Coordination water molecules as well as lattice water molecules and the proton from phosphonate groups can act as proton sources.…”

Overcoming the crystallization and designability issues in the ultrastable zirconium phosphonate framework system

“…During the past decade, significant amounts of works have been devoted to designing and synthesizing MOFs that are resistant to structural degradation induced by moisture, acids/bases, oxidants/reductants and radiation, critical features for many practical applications12345. To achieve these goals, Pearson hard and soft acid and base theory was followed67.…”

1000-fold enhancement in proton conductivity of a MOF using post-synthetically anchored proton transporters

“…However, 1 clearly has significantly lower conductivities compared to the 1_EG even under 90% rH and 90 °C, which strongly suggests lack of any such decomposition. Even the recently reported sodium and cesium sulfonate and magnesium phosphonate MOFs do not show any such decomposition under similar conditions102040.…”

“…To the best of our knowledge, there is only one report of a post synthetic anchoring of protic species (histidine) in a MOF, which provided conductivities of the order of 10 −9 Scm −1 at 146 °C and the humidity dependent conductivity was not reported18. However, the potential of MOF electrolytes to deliver high conductivities in the order of 10 −2 Scm −1 has recently been demonstrated13192021222324, which has really triggered the interest in exploring different chemical/structural modifications to push the conductivities to record levels.…”