Friedel-Crafts alkylation route for preparation of pendent side chain imidazolium-functionalized polysulfone anion exchange membranes for fuel cells
Graphical abstract
Introduction
In recent years, alkaline anion exchange membrane fuel cells (AAEMFCs) have drawn increasingly attentiveness by reason of the higher reaction kinetics in basic environments [1], [2], [3], [4], [5], [6], thus non-precious metals can be utilized as catalyst and reduce commercial costs [7], [8], [9]. As the essential compound of AAEMFCs, anion exchange membranes (AEMs) act as the separator and conductive support.[10]
The conventional method to prepare AEMs involves two steps: chloromethylation and quaternary amination. Particularly, chloromethylation is conducted by using chloromethyl methyl ether (CME) or chloromethyl octylether (CMOE), which provides excellent conversions and high yields [11]. Unfortunately, CME has been restricted to use since 1970s due to its carcinogenic and hazardous, and the same problem to CMOE [12], [13]. Recent methods to avoid the use of chloromethylation reagents are as following: (1) Friedel-Crafts acylation route [14], [15], (Scheme 1(1)), unfortunately, hydroxide ions attack the ketone after acylation reaction so that the anion exchange membrane has poor alkaline stability[16], [17]; Although the reduction of the ketone group to the methylene form can effectively solve this problem [15], the step of reducing the ketone group increases the difficulty of the reaction, making the reaction process more complicated, which is not conducive to simplifying the reaction process. (2) alkalinization of polymers containing uncharged functional groups using a brominating agent or methyl iodide [12], [18], [19], [20], (Scheme 1(2)); (3) N-Bromosuccinimide (NBS) acts as a brominating agent and bromination occurs with a benzyl or allyl-containing AEM material in the backbone structure, and then the quaternization reaction with the cation is performed to prepare anion exchange membrane [5], [21], [22], [23], (Scheme 1(3)); (4) preparing the anion exchange membrane by monomer polymerization after synthesis of the quaternized functional monomer [24], [25], [26], [27], (Scheme 1(4)). However, special groups, such as uncharged functional groups, a benzyl or allyl, functional monomer on polymer materials are required in methods (2) through (4), which limits the practical applications of these methods on commonly high performance polymers.
The Friedel-Crafts alkylation reaction means the preparation of alkyl carbocation by haloalkanes under the action of Lewis acid catalysts (AlCl3, FeCl3, SnCl4, etc.), which act as electrophiles attacking the benzene ring, then benzene ring forms carbocations and losses the proton to give the alkylbenzene [28], [29]. It has no special functional group requirements on the polymer materials since Friedel-Crafts alkylation is a characteristic reaction of benzene ring. Compared with the acylation reagents, Friedel-Crafts alkylation reagents do not require the alkaline unstable ketone, and therefore improve stability of the AEMs. More importantly, it is easy to introduce a flexible pendent functional side chain in AEMs through Friedel-Crafts alkylation, by designing hydrophobic haloalkane with -(CH2)n- spacers, which could effectively promote the construction of hydrophilic/hydrophobic micro-phase separation structures. Recent studies [30], [31], [32] on AMEs morphology have shown the continuous hydrophilic domains promote OH- transfer, and the connectivity of the hydrophobic domains inhibit excessive membrane swelling. Increasing the flexibility of the functional side chains [33], [34], [35], [36] can effectively solve the challenging issues that with the growth of IECs, ion conductivities increase, however, dimensional stability decreases due to excessive swelling of the membranes, and alkaline stability declines due to the growing chance of OH- attacking on the methylene groups that connect the functional groups to the polymer backbone [37], [38], [39]. Though it is an effective way to synthesis complex organics [40], [41], [42], [43], [44], as far as we know, it has no application on the preparation of AEMs.
In this work, polysulfone based anion exchange membrane containing pendent imidazole functionalized side chain are synthesized by the novel Friedel-Crafts alkylation route (Scheme 2), which is free of toxic carcinogenic chloromethylation reagents and has advantages over the above mentioned chloromethylation free methods. A new kind of alkylation reagent with -(CH2)4- spacer, 1-chlorobutyl- 2, 3-dimethylimidazole chloride [CBDMIm] Cl is synthesized and introduces a pendent alkyl functional side chain on polysulfone. The excellent hydrophilic/hydrophobic micro-phase separation structures make the PSf-BDMImOH anion exchange membranes prepared in this study exhibit higher IEC normalized ion conductivity than other AEMs prepared without chloromethylation reagent. More delightfully is that the swelling ratio of the membranes is very low and ion conductivity-normalized swelling ratio is the lowest even at 80 °C. It also has excellent alkaline stability.
Section snippets
Material
Udel P3500 polysulfone (PSf), Potassium hydroxide (KOH), H2SO4 (92.8%), N-methyl pyrrolidone (NMP), hydrochloric acid (HCl, 12 wt%) ethanol, dichloromethane(CH2Cl2), anhydrous aluminum chloride (AlCl3), 1,2-dimethylimidazole (DmIm), 4-Chloro-1-butanol were obtained commercially. Before using the deionized water was continuous boiled to remove carbon dioxide (CO2).
Synthesis of 1- hydroxybutyl- 2, 3-dimethylimidazole chloride ([HBDMIm] Cl)
A certain proportion of DmIm and 4-chloro-1-butanol were dissolved in an appropriate amount of anhydrous ethanol, and then stirred
Structure characterization
Fig. 1 shows the 1H NMR spectra of DmIm, 4-Chloro-1-butanol, [HBDMIm] Cl, PSf and PSf-BDMImCl. In 1H NMR spectrum of DmIm the peaks of Ha, Hb, Hc, Hd, are arised at δ = 2.24, δ = 3.52, δ = 6.68, δ = 6.97 ppm, respectively. The triplets atδ= 3.80 ppm, δ = 3.62 ppm in 1 H NMR spectrum of 4-Chloro-1-butanol are attributed to the methylene protons He, Hh, respectively, and the multiple at 1.94 ppm are assigned to Hf, Hg. [HBDMIm]Cl has been synthesized after the menshutkin reaction of DmIm and
Conclusions
PSf-BDMImOH membranes with pendent imidazole functionalized side chains were prepared by Friedel-Crafts alkylation instead of chloromethylation. 1H NMR and FT-IR spectra confirmed the successful synthesis of PSf-BDMImCl. The new route is both environmentally friendly and non-toxic, avoiding the use of chloromethylation reagents. In addition, SAXS and TEM results showed that good hydrophilic/hydrophobic micro-phase separation structure has formed in the membrane. The IECs of the PSf-BDMImOH
Acknowledgement
The authors thank the National Natural Science Foundation of China (21476044, 21406031 and 21776034), the National Key Research and Development Program of China (2016YFB0101203), the Joint Funds of the National Natural Science Foundation of China (U1663223) and the Changjiang Scholars Program (T2012049) for financial support of this work.
References (63)
- et al.
High performance PtPdAu nano-catalyst for ethanol oxidation in alkaline media for fuel cell applications
Int. J. Hydrog. Energy
(2011) - et al.
A high-performance integrated electrode for anion-exchange membrane direct ethanol fuel cells
Int. J. Hydrog. Energy
(2011) - et al.
The effect of electrode parameters on the performance of anion exchange polymer membrane fuel cells
Int. J. Hydrog. Energy
(2011) - et al.
Stability challenge in anion exchange membrane for fuel cells
Curr. Opin. Chem. Eng.
(2016) - et al.
The evolution of the performance of alkaline fuel cells with circulating electrolyte
J. Power Sources
(2004) - et al.
Anion exchange membranes for alkaline fuel cells: a review
J. Membr. Sci.
(2011) - et al.
Developing a polysulfone-based alkaline anion exchange membrane for improved ionic conductivity
J. Membr. Sci.
(2009) - et al.
Quaternized polybenzimidazoles with imidazolium cation moieties for anion exchange membrane fuel cells
J. Membr. Sci.
(2014) - et al.
A safer route for preparation of anion exchange membrane from inter-polymer film and performance evaluation in electrodialytic application
J. Membr. Sci.
(2014) - et al.
Poly(2,6-dimethyl-1,4-phenylene oxide) containing imidazolium-terminated long side chains as hydroxide exchange membranes with improved conductivity
J. Membr. Sci.
(2016)
Quaternized triblock polymer anion exchange membranes with enhanced alkaline stability
J. Membr. Sci.
Characterization of a soluble poly(ether ether ketone) anion exchange membrane for fuel cell application
Int. J. Hydrog. Energy
A stable anion exchange membrane based on imidazolium salt for alkaline fuel cell
J. Membr. Sci.
A facile functionalized routine for the synthesis of imidazolium-based anion-exchange membrane with excellent alkaline stability
J. Membr. Sci.
Quaternized poly(methyl methacrylate-co-butyl acrylate-co-vinylbenzyl chloride) membrane for alkaline fuel cells
J. Power Sources
Bis-imidazolium-based anion-exchange membranes for alkaline fuel cells
J. Power Sources
Construction of ion transport channels by grafting flexible alkyl imidazolium chain into functional poly(arylene ether ketone sulfone) as anion exchange membranes
Int. J. Hydrog. Energy
Design of pendent imidazolium side chain with flexible ether-containing spacer for alkaline anion exchange membrane
J. Membr. Sci.
In situ compatibilization of polyolefin and polystyrene using Friedel-Crafts alkylation through reactive extrusion
Polymer
Anion exchange membranes based on quaternized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene for direct methanol alkaline fuel cells
J. Membr. Sci.
Imidazolium-functionalized polysulfone hydroxide exchange membranes for potential applications in alkaline membrane direct alcohol fuel cells
Int. J. Hydrog. Energy
Preparing alkaline anion exchange membrane with enhanced hydroxide conductivity via blending imidazolium-functionalized and sulfonated poly(ether ether ketone)
J. Power Sources
Enhancing the hydroxide conductivity of imidazolium-functionalized polysulfone by incorporating organic microsphere with ionic brushes
J. Membr. Sci.
Anion conductive aromatic membrane of poly(tetra phenyl ether sulfone) containing hexa-imidazolium hydroxides for alkaline fuel cell application
Solid State Ion.
Poly(arylene ether ketone) with pendant pyridinium groups for alkaline fuel cell membranes
Int. J. Hydrog. Energy
Fuel cells: operating flexibly
Nat. Energy
Highly conductive and durable poly(arylene ether sulfone) anion exchange membrane with end-group cross-linking
Energy Environ. Sci.
Hydrocarbon-based polymer electrolyte membranes: importance of morphology on ion transport and membrane stability
Chem. Rev.
Silver-carbon electrocatalyst for air cathodes in alkaline fuel cells
J. Appl. Electrochem.
Alkaline stability of poly(phenylene)-based anion exchange membranes with various cations
J. Polym. Sci. Part B Polym. Phys.
Influence of sulfone linkage on the stability of aromatic quaternary ammonium polymers for alkaline fuel cells
J. Electrochem. Soc.
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