A Simple New Route to Covalent Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes

Abstract

The development of proton exchange membranes as electrolytes for polymer electrolyte fuel cells operating at intermediate temperatures has been achieved combining two approaches: the preparation of a cross-linked polymer and the formation of covalent organic/inorganic hybrids. A covalently crosslinked sulfonated polyetheretherketone with elevated degree of sulfonation (DS ) 0.8) was prepared by reaction with HSO 3 Cl (SOPEEK). No degradation of PEEK was detected upon sulfonation, but only cross-linking via sulfonic groups with formation of SO 2 moieties was observed. The extent of ramification was calculated by analyzing the 1 H nuclear magnetic resonance (NMR) spectra of the products and resulted in 20% of the total amount of -SO 3 H groups present in the polymer. The solubility of the -SO 2 Cl precursor in organic solvents allowed easy carrying out of functionalization reactions in homogeneous conditions by lithiation and subsequent reaction with SiCl 4 , thus introducing covalenly linked silicon moieties (SOSiPEEK) at the ratios 1:0.25 and 1:0.50 per monomeric unit. The products were characterized by 1 H and 13 C NMR, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

Analysis of Temperature-Promoted and Solvent-Assisted Cross-Linking in Sulfonated Poly(ether ether ketone) (SPEEK) Proton-Conducting Membranes

“…38 Simple condensation products, for example, by sSsOsSs bonds, which have been reported in annealed ionomers 39 and absorb around 1450 cm -1 , were not observed here, as shown in the inset spectrum in Figure 6a.…”

Proton Mobility in Sulfonated PolyEtherEtherKetone (SPEEK): Influence of Thermal Crosslinking and Annealing

“…There are several strategies that might be followed to further improve the properties of SAP and find an optimal balance between mechanical stability on the one hand and proton conductivity on the other, including (i) the introduction of a secondary phase for the realization of composite polymers [22][23][24][25], (ii) the formation of covalent cross-linking bonds between macromolecular chains, realized by innovative chemical synthesis [26,27] or by solvothermal treatments [28,29].…”

Composite polymer electrolytes of sulfonated poly-ether-ether-ketone (SPEEK) with organically functionalized TiO2

“…Several techniques can be used to obtain organic/inorganic hybrids [13][14][15][16]. In this work, we have dispersed an inorganic component in an organic polymer, obtaining a composite that belongs to Class I hybrids, according to the classification by Judeinstein and Sanchez [17].…”