Conjugated Microporous Polymer with C≡C and C–F Bonds: Achieving Remarkable Stability and Super Anhydrous Proton Conductivity

Abstract

Introducing nonvolatile liquid acids into porous solids is a promising solution to construct anhydrous proton-conducting electrolytes, but due to weak coordination or covalent bonds building these solids, they often suffer from structural instability in acidic environments. Herein, we report a series of steady conjugated microporous polymers (CMPs) linked by robust alkynyl bonds and functionalized with perfluoroalkyl groups and incorporate them with phosphoric acid. The resulting composite electrolyte exhibits high anhydrous proton conductivity at 30−120 °C (up to 4.39 × 10 −3 S cm −1 ), and the activation energy is less than 0.4 eV. The excellent proton conductivity is attributed to the hydrophobic pores that provide nanospace for continuous proton transport, and the hydrogen bonding between phosphoric acid and perfluoroalkyl chains of CMPs promotes short-distance proton hopping from one side to the other.

Covalent‐Organic Frameworks (COFs) as Proton Conductors

“…[23] Moreover, conjugated microporous polymers (CMPs), a special class under aromatic polymers were also tested for solid-state proton conduction by several groups due to its numerous superiority such as light element composition, extended π-conjugation, aromaticity, and harsh condition stability. [24,25] Employing such type of perfluorinated polyelectrolytes, and varieties of aromatic polymers as stated is no doubt a good choice for developing solid-state proton conductors, but the major barrier is the high cost-intensivity, limited operating temperature (0-80 °C), insufficient durability, and high water and/or methanol permeability, which not only restrict them from their maximum efficiency but also makes disable for successful employment as PEM in high-temperature fuel cells (HT-PEMFCs). Moreover, the heterogeneous random structure and the amorphous nature of such polymers are the major drawback to analyze the conduction mechanism efficiently and hence understanding the structure-property relationship at the molecular level.…”

“…Herein, we intend to provide a timeline of the important events on the development of proton‐conducting materials, which is depicted in Figure 1 for at a glance visualization to the readers. [ 8,12–37 ] The proton‐conducting materials development journey was started in 1806 by C. J. T von Grotthuss through the discovery of protonic species in an aqueous solution. [ 12 ] Later, in 1877, the electrical transport in ice was verified, and after that, Bjerrum, Eigen, and co‐workers extensively studied the proton conduction in ice; however, neither pure nor doped water was found to be a good conductor of protons.…”

“…[ 8 ] Therefore, in search for cheaper, commercially viable, and good conducting properties alternative to the Nafion and similar materials, some other chemically and thermally stable sulfonated aromatic polymers, such as poly(styrene sulfonic acid) and the analogous polymers of phenol sulfonic acid resin and poly(trifluorostyrene sulfonic acid), were also tested as proton conductors. [ 8 ] Furthermore, from 1970 to till now, in search of efficient and reliable proton‐conducting materials, a continuous effort was devoted to develop several new alternative solid‐state proton‐conducting materials, as depicted in Figure 1, [ 8,15–38 ] among which in 1976, Shilton and Howe developed hydrates of uranylphosphate (HUO 2 PO 4 ·3H 2 O, HUPs) as solid‐state proton conductors, which displayed high conductivity (4 × 10 −3 S cm −1 ) even at room temperature attributed to the continuous network of water molecules present between the charged layers. [ 17 ] Along the same line, in the early 1980s, solid oxo‐acid and their family (MHSO 4 where M = Rb, Cs) [ 8 ] along with perovskite‐type ceramic oxide were developed by Kreuer, [ 21 ] which displayed conductivity up to 10 −2 S cm −1 even at higher operating temperature (600–1000 °C) than Nafion.…”

Advances in porous organic polymers: syntheses, structures, and diverse applications

“…147 Zhang et al incorporated phosphoric acid into porous solids through Sonogashira coupling of 1,3,5-tris(4-ethynylphenyl)benzene with various aliphatic perfluoro monomers (Figure 20). 148 The obtained electrolytes of CMP polymers had a low activation energy (0.4 eV) and high proton conductivity (4.39  10 -3 S cm -1 ), due to their hydrophobic pores and hydrogen bonding between phosphoric acid and the perfluoroalkyl chains of the BET surface area of 962 m 2 g −1 and a pore size of 1.8 nm (Figure 23). 158 The conductivity of TAPP-TFPP-COF after doping with I 2 increased from 1.12  10 -10 to 1.46  10 -7 S cm -1 ; furthermore, TAPP-…”

Host–Guest Assembly of H-Bonding Networks in Covalent Organic Frameworks for Ultrafast and Anhydrous Proton Transfer

“…As a green and effective proton carrier, so far, the accumulation of PILs into nanochannels of COFs for conductivity fields is rarely investigated. , Regarding the appropriate proton carrier for anhydrous conductivity, phosphoric acids and ionic liquids are ideal alternatives and have been widely investigated in the past decades . Considering that stable frameworks being capable of accommodation of strong acids are limited, , the neutral ionic liquids provide us more possibilities to design proton-conducting materials.…”