Influences of non-ionic branches on the properties of the anion exchange membranes based on imidazolium functionalized poly (2, 6-dimethyl-1, 4-phenylene oxide)
Graphical abstract
Introduction
As one of the power generation devices converting chemical energy into electricity, the anion exchange membrane fuel cell (AEMFC) possesses advantages of fast oxygen reduction kinetics in alkaline medium, low fuel permeability, and usably earth-abundant catalysts like nickel and silver [1], [2], [3]. However, compared to the polymer electrolyte of proton exchange membranes (PEMs), the anion exchange membrane (AEM) is urgently needed to improve its ionic conductivity and durability from points of view of its development and practical applications [4], [5], [6]. To solve these problems, great efforts have been made to design and optimize the structure of both polymer backbones and functional cations. For instance, thermally and chemically stable polymers of poly(vinylbenzyl chloride)-based copolymers [7], polyolefins [8], and fluorene-based polymers [9] have been employed as matrix materials for membrane preparation. Zhang et al. [10] designed tetra-pyrrolidinium modified block polymer of poly(arylene ether sulfone)s and achieved a conductivity of 68 mS cm−1 at 80 °C. After exposed to 1 M NaOH at 60 °C for 16 days, the membrane still exhibited a conductivity of 57 mS cm−1 at 80 °C. In addition, various functional groups such as quaternary ammonium [11], [12], imidazolium [13], [14], phosphonium [15], guanidinium [16], [17], and metal-based cations [18], [19] have been used to modify the polymers for both hydroxide ion conduction and possible high tolerance to the nucleophilic attack of hydroxide ions. Among these quaternary cations, the imidazolium has been widely used since it could bring on the polymer with relatively high hydroxide conductivity [20], [21]. Moreover, the imidazolium ring is easy to be structurally modified via grafting for a reasonable high stability against the attack of hydroxide ions [22]. For example, Yan and co-workers have demonstrated that the sterically bulky substituents at C2 or/and N3 positions could improve alkaline stability of the imidazolium based AEMs by prevention of ring-opening mechanism [23], [24].
Generally, the ionic conductivity of the membrane electrolyte is related to its cationic concentration, water content and micro-phase structure [25]. For instance, it is reported that the conductivity of the poly(arylene ether sulfone)s-based AEMs was increased from 12 to 72 mS cm−1 at room temperature as an increase in the ion exchange capacity (IEC) from 1.34 to 2.61 mmol g−1 [26]. It is essential to the AEMs to have enough cation groups for ion conduction [27]. However, the improvement on the conductivity via this way might bring on poor mechanical property of the AEMs due to the excessive water swelling [28]. It is well known that crosslinking of the polymer backbone is the most used strategy to reinforce the mechanical strength of the polymer electrolyte membrane [21], [29], [30], [31]. However, the enhanced dimensional and mechanical stability via crosslinking are often at the expense of ionic conductivity since the chemical crosslinking might occupy cationic functional sites of the polymer [32].
As AEMs generally are operated at temperatures below the water boiling point of 100 °C, construction of appropriate express way for ion conduction with lubrication of water molecules are attractive for enhanced performance of the AEMs. It has been found that design of different side chains could bring on appropriate amphiphilic phase-separated structure and reach high ion conductivity of the AEMs [33], [34], [35], [36]. For example, Zhuang et al. [37] constructed a highly efficient ion-aggregating structure by grafting alkyl side chains of different lengths to the polysulfone backbones. The membrane possessing a six-carbon alkyl side chain exhibited a hydroxide conductivity of 108 mS cm−1 at 80 °C, which is obviously higher than that of its pristine membrane, i.e., 41 mS cm−1.
Herein, we prepared the AEMs by grafting different non-ionic side chains, including amylamine (AA), 4-phenylbutylamine (PhA), 2-ethoxyethanamine (EOA) and 3-methoxypropylamine (MOA), onto poly(phenylene oxide) (PPO) backbones and 1,2,4,5-tetramethylimidazolium as functional cationic groups. The lone pair electrons of oxygen atom allow the electron-rich ether groups to show favorable interactions with the cationic groups and water molecules. It is expected that the ether containing side chains of EOA and MOA could assist the formation of water-rich ion transport domains, which might benefit creation of appropriate microphase distribution of the AEMs for high ionic conductivity and reasonable chemical and mechanical stabilities in the alkaline conditions. In addition, AA and PhA with different hydrophilicity were grafted onto the polymer backbones, separately, to investigate the influence of the nonionic branches on the properties of the AEMs as well. All the hydrogen atoms in the grafted imidazolium ring were substituted with methyl groups in order to achieve the AEMs a high alkaline stability [38], [39]. Comprehensive characterization and investigations were made to better understand the effects of the nonionic side branches on the performance of the AEMs.
Section snippets
Materials and reagents
The polymer PPO, 2,2′-azobis-isobutyronitrile (AIBN), and N-bromosuccinimide (NBS) were purchased from Sigma-Aldrich. The 1,2,4,5-tetramethylimidazole (TMIm) and various amines including AA, PhA, EOA and MOA were purchased from TCI Development Co. Ltd. Anhydrous methanol, anhydrous ethanol, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc) were obtained from Tianjin Yongda Chemical Reagent Co. Ltd. The AIBN was recrystallized from the anhydrous methanol before use, and all the
Synthesis and characterization of AEMs
The 1H NMR spectra of PPO, BPPO, PPO-AA, Im-PPO and S-PPO membranes are shown in Fig. 1. For BPPO, the characteristic peak at 2.1 ppm is assigned to the protons of methyl groups (Hc,d and Hg), and the one at 4.3 ppm is attributed to the protons of bromomethyl groups (Hh). The degree of bromination of the BPPO could be calculated according to the ratio of integral areas of these two peaks [42]. Hereinafter, a bromination degree of 20%, which could be controlled by the addition molar ratio of NBS
Conclusions
Novel anion exchange membranes possessing different nonionic branches are fabricated based on imidazolium functionalized poly (2, 6-dimethyl-1, 4-phenylene oxide). Four kinds of side chains including amylamine, 4-phenylbutylamine, 2-ethoxyethanamine and 3-methoxypropylamine have been successfully grafted onto the polymer structure, respectively, according to 1H NMR and FTIR spectra. The side-chain structure can effectively improve the dimensional stability and control the water uptake and
CRediT authorship contribution statement
Ruiying Wan: Conceptualization, Methodology, Data curation, Validation, Writing - original draft, Investigation, Writing - review & editing. Dengji Zhang: Investigation, Data curation. Shaoshuai Chen: Software. Niya Ye: Validation. Yunfei Yang: Validation. Ronghuan He: Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We are grateful for the financial support from the National Natural Science Foundation of China (grant No. 51572044).
The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.
References (57)
- et al.
Polymeric materials as anion-exchange membranes for alkaline fuel cells
Prog. Polym. Sci.
(2011) - et al.
Advances and challenges in alkaline anion exchange membrane fuel cells
Prog. Energy Combust. Sci.
(2018) - et al.
Ion exchange membranes: New developments and applications
J. Membr. Sci.
(2017) - et al.
High alkaline resistance of benzyl-triethylammonium functionalized anion exchange membranes with different pendants
Eur. Polym. J.
(2018) - et al.
Pyrrolidinium-functionalized poly(arylene ether sulfone)s for anion exchange membranes: Using densely concentrated ionic groups and block design to improve membrane performance
J. Membr. Sci.
(2017) - et al.
Tri-quaternized poly (ether sulfone) anion exchange membranes with improved hydroxide conductivity
J. Membr. Sci.
(2016) - et al.
Well-designed mono- and di-functionalized comb-shaped poly(2,6-dimethylphenylene oxide) based alkaline stable anion exchange membrane for fuel cells
Int. J. Hydrogen Energy
(2018) - et al.
Clustered multi-imidazolium side chains functionalized alkaline anion exchange membranes for fuel cells
J. Membr. Sci.
(2017) - et al.
Imidazolium functionalized poly(aryl ether ketone) anion exchange membranes having star main chains or side chains
Renew. Energy
(2018) - et al.
Synthesis of novel guanidinium-based anion-exchange membranes with controlled microblock structures
J. Membr. Sci.
(2017)
Polysulfones with highly localized imidazolium groups for anion exchange membranes
J. Membr. Sci.
Ionic crosslinking of imidazolium functionalized poly(aryl ether ketone) by sulfonated poly(ether ether ketone) for anion exchange membranes
J. Coll. Interf. Sci.
Synthesis and characterization of anion exchange multi-block copolymer membranes with a fluorine moiety as alkaline membrane fuel cells
J. Power Sour.
Poly(arylene ether sulfone)s ionomers containing quaternized triptycene groups for alkaline fuel cells
J. Power Sour.
Functionalization of polybenzimidazole-crosslinked poly(vinylbenzyl chloride) with two cyclic quaternary ammonium cations for anion exchange membranes
J. Membr. Sci.
Self-crosslinked alkaline electrolyte membranes based on quaternary ammonium poly (ether sulfone) for high-performance alkaline fuel cells
Int. J. Hydrogen Energy
Side-chain-type imidazolium-functionalized anion exchange membranes: The effects of additional hydrophobic side chains and their hydrophobicity
J. Membr. Sci.
Hydrophilic side chain assisting continuous ion-conducting channels for anion exchange membranes
J. Membr. Sci.
Preparation and investigation of various imidazolium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes
Electrochim. Acta
Synthesis and characterization of sulfonated poly(arylene ether sulfone) copolymers containing carboxyl groups for direct methanol fuel cells
J. Membr. Sci.
Modification of poly(aryl ether ketone) using imidazolium groups as both pendants and bridging joints for anion exchange membranes
Eur. Polym. J.
Development of BPPO-based anion exchange membranes for electrodialysis desalination applications
Desalination
Anion exchange membrane with a novel quaternized ammonium containing long ether substituent
J. Membr. Sci.
Design of pendent imidazolium side chain with flexible ether-containing spacer for alkaline anion exchange membrane
J. Membr. Sci.
Quaternized poly(ether ether ketone) hydroxide exchange membranes for fuel cells
J. Membr. Sci.
Highly stable ionic-covalent cross-linked sulfonated poly(ether ether ketone) for direct methanol fuel cells
J. Power Sour.
Comb-shaped anion exchange membrane with densely grafted short chains or loosely grafted long chains?
J. Membr. Sci.
Hydrophobic side chains to enhance hydroxide conductivity and physicochemical stabilities of side-chain-type polymer AEMs
J. Membr. Sci.
Cited by (16)
Preparation and alkaline stability of polyethylene composite hydroxide exchange membranes with different cations
2023, International Journal of Hydrogen EnergyDevelopment of rigid side-chain poly(ether sulfone)s based anion exchange membrane with multiple annular quaternary ammonium ion groups for fuel cells
2022, PolymerCitation Excerpt :As revealed in Table 3, the membranes rPES(x/y)-Q exhibit the PM values of 4.4–9.0 × 10−7 cm2 s −1, which is a little higher than the reported grafted membrane [41]. Nonetheless, it is found that much lower PM is arrived for rPES(5/10)-MM than the reported membrane Im-PPO with nearly hydroxide conductivity but high IEC and WU values (Table 4) [42]. At the same time, the PM of rPES(5/20)-MPy is half of the crosslink poly (aryl ether sulfone) based copolymer C-PAES-70/30, in spite of the fact that it has a similar ion conductivity and WU, but 2.5 times of IEC value [43].
Highly alkaline stable fully-interpenetrating network poly(styrene-co-4-vinyl pyridine)/polyquaternium-10 anion exchange membrane without aryl ether linkages
2022, International Journal of Hydrogen EnergyCitation Excerpt :Furthermore, the ionic conductivities of F-IPN QPS4VP/PQ-10 AEMs vary with temperature according to the Arrhenius equation. The apparent activation energy (Ea) of the membranes ranges from 6 to 12.55 kJ/mol, which is lower than that of many reported AEMs [7,69–71], verifying the smaller energy barrier in the process of OH− transmission and the easier transmission of OH− [5,72]. In addition, by comparing with the performances of some reported AEMs (Table 2), the comprehensive performances of F-IPN QPS4VP/PQ-10 AEMs are outstanding, indicating that they have great application potential in alkaline fuel cells.
Constructing the basal nanofibers suit of layer-by-layer self-assembly membranes as anion exchange membranes
2022, Journal of Molecular LiquidsCitation Excerpt :In our opinion, the prepared AEMs with lower β values were primarily suffered from the higher p values. The alkaline stability of membrane was evaluated by monitoring the variation on hydroxide conductivities and exterior inspection [59,61]. As expected, (LBL)200/PNs and (LBL)300/PNs membranes can keep the intact, tough and flexible profile without cracks and separation while the membrane samples were immersed into 1M KOH solution for 888 h. For the (LBL)200 and (LBL)300 membranes, they could decompose into small pieces (Fig. S7) while they were immersed into 1M KOH solution for 48 h. From Fig. 7, the long-term hydroxide conductivities were steady in the range of 30–80 °C.
Operational parameters correlated with the long-term stability of anion exchange membrane water electrolyzers
2021, International Journal of Hydrogen Energy