Supramolecular Proton Conductors Self-Assembled by Organic Cages

Abstract

Proton conduction is vital for living systems to execute various physiological activities. The understanding of its mechanism is also essential for the development of state-of-the-art applications, including fuel-cell technology. We herein present a bottom-up strategy, that is, the self-assembly of Cage-1 and -2 with an identical chemical composition but distinct structural features to provide two different supramolecular conductors that are ideal for the mechanistic study. Cage-1 with a larger cavity size and more H-bonding anchors self-assembled into a crystalline phase with more proton hopping pathways formed by H-bonding networks, where the proton conduction proceeded via the Grotthuss mechanism. Small cavity-sized Cage-2 with less H-bonding anchors formed the crystalline phase with loose channels filled with discrete H-bonding clusters, therefore allowing for the translational diffusion of protons, that is, vehicle mechanism. As a result, the former exhibited a proton conductivity of 1.59 × 10 –4 S/cm at 303 K under a relative humidity of 48%, approximately 200-fold higher compared to that of the latter. Ab initio molecular dynamics simulations revealed distinct H-bonding dynamics in Cage-1 and -2 , which provided further insights into potential proton diffusion mechanisms. This work therefore provides valuable guidelines for the rational design and search of novel proton-conducting materials.

Enhanced Proton Conductivity of an Ionic Hydrogen-Bonded Organic Framework-Embedded Nafion Matrix

“…The activation energy ( E a ) of 1 is 0.38 eV (Figure d), which belongs to the Grotthuss , mechanism ( E a < 0.40 eV) within 80–100 °C. 2 has an activation energy of 0.43 eV (Figure d), which belongs to the vehicular mechanism ( E a > 0.40 eV).…”

“…As humidity increases, more water molecules pass through the proton transport channel, the proton transport capacity increases, and the proton conductivity increases. The activation energy (E a ) of 1 is 0.38 eV (Figure 3d), which belongs to the Grotthuss 45,46 mechanism (E a < 0.40 eV) within 80−100 °C. 2 has an activation energy of 0.43 eV (Figure 3d), which belongs to the vehicular 47 mechanism (E a > 0.40 eV).…”

Space-Confined Nucleation of Semimetal-Oxo Clusters within a [H7P8W48O184]33– Macrocycle: Synthesis, Structure, and Enhanced Proton Conductivity

“…Finally, on the basis of the Arrhenius equation σ T = σ 0 exp(− E a / k B T ), the activation energy of E a = 0.61 eV was obtained for DMA-KNaLi-As 10 under 70% RH (Figure e). According to the previous work, such proton transfer is mainly via diffusive routes and can be explained in terms of the vehicle mechanism (typically E a > 0.4 eV). ,,− Meanwhile, the stable proton-conducting performance of DMA-KNaLi-As 10 was validated, as there was no obvious change of the conductivity value (85 °C and 70% RH) being observed over the course of 6 h (Figure S9). The phase purity and stability of DMA-KNaLi-As 10 were confirmed from a comparison of their powder XRD patterns (Figure f), FESEM images (Figure S10), EDX spectra (Figure S11), and FT-IR spectra (Figure S12) before and after the impedance measurements.…”

Recent advances in the applications of porous organic cages

“…Yang et al 116 synthesized two porous organic cages by the cycloimination of aldehyde-containing precursors and tris(2-aminoethyl)amine (Cage 1) or tris(3-aminopropyl)amine (Cage 2). These two cages were different in shape, cavity size, and H-bonding anchor.…”