Superprotonic Conductivity of UiO-66 with Missing-Linker Defects in Aqua-Ammonia Vapor

Abstract

The design and preparation of proton-conducting metal–organic frameworks (MOFs) with superconductivity are of significance for the proton-exchange membrane fuel cell (PEMFC). Introducing functional structural defects to enhance proton conductivity is a good approach. Here, we synthesized a series of UiO-66 (first synthesized in the University of Oslo) with missing-linker defects and investigated the effect of defect numbers on the proton conductivity of the samples. Among them, 60-UiO-66-1.8 (60 represents the synthesis temperature and 1.8 the number of defects) prepared with 3-mercaptopropionic acid as a modulator has the best proton conductivity, which is 3 × 10–2 S cm–1 at 100 °C and under 98% relative humidity (RH). The acidic sites induced by missing-linker defects further promote the chemisorption of ammonia molecules, resulting in the formation of a richer hydrogen-bond network and hence boosting the proton conductivity to 1.04 × 10–1 S cm–1 at 80 °C, which is one of the highest values among the reported MOF-based proton conductor. Therefore, this work provides a new strategy for enhancing proton conduction in MOF-based materials.

New Type of Nanocomposite CsH2PO4-UiO-66 Electrolyte with High Proton Conductivity

“…The FTIR spectroscopy data for the systems based on the alkaline metal acid salts of the (M m H n (XO 4 ) p ) family and silica show that the formation of the composites occurs through the weak hydrogen bonds between salt protons and the surface OH − groups of the highly dispersed silica [ 37 , 47 , 48 ]. A similar process involving the partial sorption of the protons of CsH 2 PO 4 by the oxygen atoms of Zr clusters and the carboxylic groups of terephthalates [ 49 , 50 , 51 , 52 ] takes place in the CsH 2 PO 4 –UiO-66 system, which results in a weakening of the hydrogen bonds and a strengthening of the P-O bonds, leading to an increase in the mobility of protons.…”

Effect of Missing-Linker Defects and Ion Exchange on Stability and Proton Conduction of a Sulfonated Layered Zr-MOF

“…Ion-conducting materials are fundamentally of great importance to the development of energy storage and conversion devices, including fuel cells and batteries. While there is a growing number of papers concerning defective MOFs, those characterizing the relationship between defects and proton conductivity are only a few. ,− All these described defective proton-conducting MOFs have a zirconium cluster as a network node, and defects in the materials are created at the synthesis stage. All materials are also three-dimensional (3D), but they differ in connectivity (UiO-66 and UiO-66-SO 3 H are 12-connected, while MOF-808 is 6-connected) and ligand nature (only UiO-66-SO 3 H has a hydrophilic linker; ESI, Table S1).…”

“…In place of the missing linker, coordination unsaturated sites (CUS) appear on the metal cluster, which can provide both access to the metal center and a platform for further modification. 4 Materials with such defects, due to the presence of Lewis-type acidity and an improved sorption capacity, can be applied in catalysis, 5 decontamination, 6 dyes absorption and degradation, 7 sorption, 8 drug delivery, 9 sensing, 10 as well as charge transport, including ionic conductivity. 11−13 Ion-conducting materials are fundamentally of great importance to the development of energy storage and conversion devices, including fuel cells and batteries.…”

Comparative Studies on the Proton Conductivities of Hafnium-Based Metal–Organic Frameworks and Related Chitosan or Nafion Composite Membranes

“…On the basis of these advantages, researchers have applied MOFs to the field of proton conduction and achieved some impressive research results. For example, ultrahigh proton conductivities (σ) of some MOFs can be obtained, such as {[Co­(4,4′-bipy)­(H 2 O) 4 ]­(Hbtc)·(H 2 O) 1.5 } n [σ = 1.49 × 10 –1 S·cm –1 at 80 °C and 98% relative humidity (RH)], [Co­(DDPP)]·5H 2 O (σ = 3.9 × 10 –2 S·cm –1 at 80 °C and 97% RH), Cr-MIL-88B-PSA (σ = 1.58 × 10 –1 S·cm –1 at 100 °C and 85% RH), and so on. − Nevertheless, the MOFs’ bulk and grain boundaries limit the long-distance transport of protons. Moreover, the brittleness of MOFs also makes it difficult for them to be directly used as PEMs.…”