耐碱的胍盐阴离子交换膜研究进展
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摘要
近年来,碱性阴离子交换膜燃料电池的发展得到了国内外研究人员的广泛关注,其中开发具有高碱稳定性的阴离子交换膜材料成为了研究的热点和难点.除了聚合物骨架,改善离子基团的稳定性对于阴离子交换膜材料整体稳定性的提高具有关键作用.胍盐离子作为一种新型的离子基团,分子结构中正电荷共轭分布在中心碳和3个氮原子上,电荷高度离域使得胍盐离子具有非常优异的热稳定性和化学稳定性,有望解决传统季铵盐离子在碱性条件下存在的降解问题.本文综述了近年来胍盐型阴离子交换膜材料的研究进展,其中包括胍盐阴离子交换膜材料的制备、分类以及胍盐离子的降解机理,同时对于耐碱型胍盐阴离子交换膜的结构设计进行了分析和展望.
Anion exchange membranes(AEMs) are solid polymer electrolytes that contain cationic groups covalently bound to or embedded in a polymer backbone. They act as key role of hydroxide conduction and separator between two electrodes in anion exchange membrane fuel cells(AEMFCs). To achieve high performance in AEMFCs, ideal AEMs should own high ion conductivity and good alkaline stability. Considering to the alkaline stability of AEMs, ionic groups play very important role in determining the overall stability for the AEMs apart from polymer backbones. To date, various ion conductive moieties have been investigated as new tethered ionic groups to replace conventional quaternary ammoniums(QAs) in AEMs because of the multiple degradation pathways under alkaline conditions including:(1) nucleophilic substitution(S_N2),(2) Hoffmann elimination(E2), or(3) nitrogen ylide formation. Guanidiniums are found to be a kind of novel ionic groups for the application of AEMs. In the structure of guanidinium, the positive charge is uniformly distributed over the central carbon atom and three nitrogen atoms, leading to stabilized charge delocalization and good thermal and chemical stability. There are six substitutions distributed over three N atoms which can be easily tuned by a mature and feasible route. Additionally, the kinetics of hydrogen evolution/oxidation reaction(HER/HOR) and ORR catalyzed by Pt and carbon-based non precious metal could be greatly enhanced through using guanidiniums. Guanidinium cations can be introduced into the polymer backbone easily by the synthetic methods as follows:(1) halomethylation of a phenyl group and subsequent amination with pentalkylguanidine;(2) nucleophilic substitution of a Vilsmeier salt and a secondary amine;(3) activated fluoroamine reaction;(4) nucleophilic substitution of alkyl halid and guanidine to prepare guanidinium functional monomer;(5) polycondensation between guanidine hydrochloride and diamine. Recently, several types of guanidinium-functionalized AEMs have been explored including benzylic guanidinium AEMs, alkylic guanidinium AEMs and phenylic guanidinium AEMs. Some of the AEMs have been proven to possess excellent ion conductivity, and some have been used in AEMFCs and show good electrochemical performance. Considering to degradation mechanism of guanidinium, it can be concluded as a nucleophilic addition-elimination reaction: firstly the center C atom is attacked by OH~-and an intermediate is obtained(addition reaction); then one of N atoms combines with the H atom and eliminates from the intermediate(elimination reaction); finally the degradation products urea and amine are formed. It is worth noting that the degradation process of guanidinium is evidently different from quaternary ammoniums. Their degradation reaction sites only occur at the central carbon atom rather than the benzyl carbon which indicate the promising stability for guanidinium. Though the stabilities of guanidiniums are under debate by now, the usability of guanidiniums as ionic group is still a topic worthy of study. On the one hand, almost all of the studies are confined to guanidiniums with methyl groups substituted at the N1 and N3 positions, hence comprehensive and systematic analysis of the structure-stability relationship of guanidinium cations in alkaline media is still rarely developed. On the other hand, the degradation process of guanidiniums is only speculated by a few studies in theoretical way, more specific experimental studies of this process are badly needed to prove it. Therefore, revealing the structure-stability relationship and the detailed degradation mechanism are vital to design alkaline stable guanidinums which can be applied to AEMs preparation in the future. In addition, the polymer backbone is also very important to improve the stability of guanidiniums based AEMs. More guanidiniums based AEMs with various structures should be designed and prepared. The ion conductivity, alkaline stability and cell performace should be assessed comprehensively to figure out the relationship between the structures and properties of AEMs, and finally the preparation of high performance anion exchange membranes can be achieved.
Anion exchange membranes(AEMs) are solid polymer electrolytes that contain cationic groups covalently bound to or embedded in a polymer backbone. They act as key role of hydroxide conduction and separator between two electrodes in anion exchange membrane fuel cells(AEMFCs). To achieve high performance in AEMFCs, ideal AEMs should own high ion conductivity and good alkaline stability. Considering to the alkaline stability of AEMs, ionic groups play very important role in determining the overall stability for the AEMs apart from polymer backbones. To date, various ion conductive moieties have been investigated as new tethered ionic groups to replace conventional quaternary ammoniums(QAs) in AEMs because of the multiple degradation pathways under alkaline conditions including:(1) nucleophilic substitution(S_N2),(2) Hoffmann elimination(E2), or(3) nitrogen ylide formation. Guanidiniums are found to be a kind of novel ionic groups for the application of AEMs. In the structure of guanidinium, the positive charge is uniformly distributed over the central carbon atom and three nitrogen atoms, leading to stabilized charge delocalization and good thermal and chemical stability. There are six substitutions distributed over three N atoms which can be easily tuned by a mature and feasible route. Additionally, the kinetics of hydrogen evolution/oxidation reaction(HER/HOR) and ORR catalyzed by Pt and carbon-based non precious metal could be greatly enhanced through using guanidiniums. Guanidinium cations can be introduced into the polymer backbone easily by the synthetic methods as follows:(1) halomethylation of a phenyl group and subsequent amination with pentalkylguanidine;(2) nucleophilic substitution of a Vilsmeier salt and a secondary amine;(3) activated fluoroamine reaction;(4) nucleophilic substitution of alkyl halid and guanidine to prepare guanidinium functional monomer;(5) polycondensation between guanidine hydrochloride and diamine. Recently, several types of guanidinium-functionalized AEMs have been explored including benzylic guanidinium AEMs, alkylic guanidinium AEMs and phenylic guanidinium AEMs. Some of the AEMs have been proven to possess excellent ion conductivity, and some have been used in AEMFCs and show good electrochemical performance. Considering to degradation mechanism of guanidinium, it can be concluded as a nucleophilic addition-elimination reaction: firstly the center C atom is attacked by OH~-and an intermediate is obtained(addition reaction); then one of N atoms combines with the H atom and eliminates from the intermediate(elimination reaction); finally the degradation products urea and amine are formed. It is worth noting that the degradation process of guanidinium is evidently different from quaternary ammoniums. Their degradation reaction sites only occur at the central carbon atom rather than the benzyl carbon which indicate the promising stability for guanidinium. Though the stabilities of guanidiniums are under debate by now, the usability of guanidiniums as ionic group is still a topic worthy of study. On the one hand, almost all of the studies are confined to guanidiniums with methyl groups substituted at the N1 and N3 positions, hence comprehensive and systematic analysis of the structure-stability relationship of guanidinium cations in alkaline media is still rarely developed. On the other hand, the degradation process of guanidiniums is only speculated by a few studies in theoretical way, more specific experimental studies of this process are badly needed to prove it. Therefore, revealing the structure-stability relationship and the detailed degradation mechanism are vital to design alkaline stable guanidinums which can be applied to AEMs preparation in the future. In addition, the polymer backbone is also very important to improve the stability of guanidiniums based AEMs. More guanidiniums based AEMs with various structures should be designed and prepared. The ion conductivity, alkaline stability and cell performace should be assessed comprehensively to figure out the relationship between the structures and properties of AEMs, and finally the preparation of high performance anion exchange membranes can be achieved.
引文
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5 He G,Li Z,Zhao J,et al.Nanostructured ion-exchange membranes for fuel cells:Recent advances and perspectives.Adv Mater,2015,27:5280-5295
6 Li N,Leng Y,Hickner M,et al.Highly stable,anion conductive,comb-shaped copolymers for alkaline fuel cells.J Am Chem Soc,2013,135:10124-10133
7 Pan J.A study of alkaline polymer electrolytes for fuel cell application(in Chinese).Doctor Dissertation.Wuhan:Wuhan University,2012[潘婧.燃料电池用碱性聚合物电解质研究.博士学位论文.武汉:武汉大学,2012]
8 Li N,Guiver M.Ion transport by nanochannels in ion-containing aromatic copolymers.Macromolecules,2014,47:2175-2198
9 Dong X,Hou S,Mao H,et al.Novel hydrophilic-hydrophobic block copolymer based on cardo poly(arylene ether sulfone)s with bis-quaternary ammonium moieties for anion exchange membranes.J Membr Sci,2016,518:31-39
10 Gu L,Sun Z,Yan F,et al.Progress of alkaline anion exchange membrane(in Chinese).J Funct Polym,2016,29:153-162[顾梁,孙哲,严锋,等.碱性阴离子交换聚合物膜研究进展.功能高分子学报,2016,29:153-162]
11 Dekel D,Amar M,Willdorf S,et al.Effect of water on the stability of quaternary ammonium groups for anion exchange membrane fuel cell applications.Chem Mater,2017,29:4425-4431
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13 Marino M,Kreuer K.Alkaline stability of quaternary ammonium cations for alkaline fuel cell membranes and ionic liquids.ChemSusChem,2015,8:513-523
14 Lin B,Qiu L,Qiu B,et al.A soluble and conductive polyfluorene ionomer with pendant imidazolium groups for alkaline fuel cell applications.Macromolecules,2011,44:9642-9649
15 Liu Y,Zhang B,Kinsinger C,et al.Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide)random copolymer functionalized with a bulky phosphonium cation.J Membr Sci,2016,506:50-59
16 Zhang B,Gu S,Wang J,et al.Tertiary sulfonium as a cationic functional group for hydroxide exchange Membranes.RSC Adv,2012,2:12683-12685
17 Zha Y,Disabb-Miller M,Johnson Z,et al.Metal-cation-based anion exchange membranes.J Am Chem Soc,2012,134:4493-4496
18 Wang J,Li S,Zhang S.Novel hydroxide-conducting polyelectrolyte composed of an poly(arylene ether sulfone)containing pendant quaternary guanidinium groups for alkaline fuel cell applications.Macromolecules,2010,43:3890-3896
19 Duan H F,Zhang S B,Lin Y J,et al.Progress in the research of guanidinium ionic liquids(in Chinese).Chin J Org Chem,2006,10:1335-1342[段海峰,张所波,林英杰,等.胍盐离子液体的研究进展.有机化学,2006,10:1335-1342]
20 Konopka D,Johnson M,Errico M,et al.Oxidation and oxygen reduction on polycrystalline platinum in aqueous tetramethylguanidine alkaline electrolyte.Electrochem Solid-State Lett,2012,15:B17-B19
21 Li S,Lin Y,Zhang S,et al.Guanidine/Pd(OAc)2-catalyzed room temperature Suzuki cross-coupling reaction in aqueous media under aerobic conditions.J Org Chem,2006,11:4067-4072
22 Wang J H.Synthesis and properties of quaternized poly(arylene ether)s as anion exchange membranes(in Chinese).Doctor Dissertation.Changchun:Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,2010[王俊华.聚芳醚基均相阴离子交换膜材料的制备与性质研究.博士学位论文.长春:中国科学院长春应用化学研究所,2010]
23 Lin X,Wu L,Liu Y,et al.Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells.J Power Sources,2012,217:373-380
24 Liu L,Li Q,Dai J,et al.A facile strategy for the synthesis of guanidinium-functionalized polymer as alkaline anion exchange membrane with improved alkaline stability.J Membr Sci,2014,453:52-60
25 Zhang Q,Li S,Zhang S.A novel guanidinium grafted poly(aryl ether sulfone)for high-performance hydroxide exchange membranes.Chem Commun,2010,46:7495-7497
26 Kim D,Labouriau A,Guiver M,et al.Guanidinium-functionalized anion exchange polymer electrolytes via activated fluorophenylamine reaction.Chem Mater,2011,23:3795-3797
27 Kim D,Fujimoto C,Hibbs M,et al.Resonance stabilized perfluorinated ionomers for alkaline membrane fuel cells.Macromolecules,2013,46:7826-7833
28 Xue B,Dong X,Li Y,et al.Synthesis of novel guanidinium-based anion-exchange membranes with controlled microblock structures.JMembr Sci,2017,537:151-159
29 Qu C,Zhang H,Zhang F,et al.A high-performance anion exchange membrane based on bi-guanidinium bridged polysilsesquioxane for alkaline fuel cell application.J Mater Chem,2012,22:8203-8207
30 Chen Y,Tao Y,Wang J,et al.Comb-shaped guanidinium functionalized poly(ether sulfone)s for anion exchange membranes:Effects of the spacer types and lengths.J Polym Sci Part A Polym Chem,2017,55:1313-1320
31 Sajjada S,HongY,Liu F.Synthesis of guanidinium-based anion exchange membranes and their stability assessment.Polym Adv Technol,2014,25:108-116
32 Sherazi T,Zahoor S,Raza R,et al.Guanidine functionalized radiation induced grafted anion-exchange membranes for solid alkaline fuel cells.Int J Hydrog Energy,2015,40:786-796
33 Cheng J,Yang G,Zhang K,et al.Guanidimidazole-quanternized and cross-linked alkaline polymer electrolyte membrane for fuel cell application.J Membr Sci,2016,501:100-108
34 Mohanty A,Bae C.Mechanistic analysis of ammonium cation stability for alkaline exchange membrane fuel cells.J Mater Chem A,2014,2:17314-17320
35 Li W,Wang S,Zhang X,et al.Degradation of guanidinium-functionalized anion exchange membrane during alkaline environment.Int JHydrog Energy,2014,39:13710-13717
36 Fukui K.Role of frontier orbitals in chemical reactions.Science,1982,218:747-754
37 Pernpointner M,Hashmi A S K.Fully relativistic,comparative investigation of gold and platinum alkyne complexes of relevance for the catalysis of nucleophilic additions to alkynes.J Chem Theory Comput,2009,5:2717-2725
2 Borup R,Meyers J,Pivovar B.et al.Scientific aspects of polymer electrolyte fuel cell durability and degradation.Chem Rev,2007,107:3904-3951
3 Merle G,Wessling M,Nijmeijer K.Anion exchange membranes for alkaline fuel cells:A review.J Membr Sci,2011,377:1-35
4 Varcoe J,Atanassov P,Dekel D,et al.Anion exchange membranes in electrochemical energy systems.Energy Environ Sci,2014,7:3135-3191
5 He G,Li Z,Zhao J,et al.Nanostructured ion-exchange membranes for fuel cells:Recent advances and perspectives.Adv Mater,2015,27:5280-5295
6 Li N,Leng Y,Hickner M,et al.Highly stable,anion conductive,comb-shaped copolymers for alkaline fuel cells.J Am Chem Soc,2013,135:10124-10133
7 Pan J.A study of alkaline polymer electrolytes for fuel cell application(in Chinese).Doctor Dissertation.Wuhan:Wuhan University,2012[潘婧.燃料电池用碱性聚合物电解质研究.博士学位论文.武汉:武汉大学,2012]
8 Li N,Guiver M.Ion transport by nanochannels in ion-containing aromatic copolymers.Macromolecules,2014,47:2175-2198
9 Dong X,Hou S,Mao H,et al.Novel hydrophilic-hydrophobic block copolymer based on cardo poly(arylene ether sulfone)s with bis-quaternary ammonium moieties for anion exchange membranes.J Membr Sci,2016,518:31-39
10 Gu L,Sun Z,Yan F,et al.Progress of alkaline anion exchange membrane(in Chinese).J Funct Polym,2016,29:153-162[顾梁,孙哲,严锋,等.碱性阴离子交换聚合物膜研究进展.功能高分子学报,2016,29:153-162]
11 Dekel D,Amar M,Willdorf S,et al.Effect of water on the stability of quaternary ammonium groups for anion exchange membrane fuel cell applications.Chem Mater,2017,29:4425-4431
12 Edson J,Macomber C,Pivovar B,et al.Hydroxide based decomposition pathways of alkyltrimethylammonium cations.J Membr Sci,2012,399:49-59
13 Marino M,Kreuer K.Alkaline stability of quaternary ammonium cations for alkaline fuel cell membranes and ionic liquids.ChemSusChem,2015,8:513-523
14 Lin B,Qiu L,Qiu B,et al.A soluble and conductive polyfluorene ionomer with pendant imidazolium groups for alkaline fuel cell applications.Macromolecules,2011,44:9642-9649
15 Liu Y,Zhang B,Kinsinger C,et al.Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide)random copolymer functionalized with a bulky phosphonium cation.J Membr Sci,2016,506:50-59
16 Zhang B,Gu S,Wang J,et al.Tertiary sulfonium as a cationic functional group for hydroxide exchange Membranes.RSC Adv,2012,2:12683-12685
17 Zha Y,Disabb-Miller M,Johnson Z,et al.Metal-cation-based anion exchange membranes.J Am Chem Soc,2012,134:4493-4496
18 Wang J,Li S,Zhang S.Novel hydroxide-conducting polyelectrolyte composed of an poly(arylene ether sulfone)containing pendant quaternary guanidinium groups for alkaline fuel cell applications.Macromolecules,2010,43:3890-3896
19 Duan H F,Zhang S B,Lin Y J,et al.Progress in the research of guanidinium ionic liquids(in Chinese).Chin J Org Chem,2006,10:1335-1342[段海峰,张所波,林英杰,等.胍盐离子液体的研究进展.有机化学,2006,10:1335-1342]
20 Konopka D,Johnson M,Errico M,et al.Oxidation and oxygen reduction on polycrystalline platinum in aqueous tetramethylguanidine alkaline electrolyte.Electrochem Solid-State Lett,2012,15:B17-B19
21 Li S,Lin Y,Zhang S,et al.Guanidine/Pd(OAc)2-catalyzed room temperature Suzuki cross-coupling reaction in aqueous media under aerobic conditions.J Org Chem,2006,11:4067-4072
22 Wang J H.Synthesis and properties of quaternized poly(arylene ether)s as anion exchange membranes(in Chinese).Doctor Dissertation.Changchun:Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,2010[王俊华.聚芳醚基均相阴离子交换膜材料的制备与性质研究.博士学位论文.长春:中国科学院长春应用化学研究所,2010]
23 Lin X,Wu L,Liu Y,et al.Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells.J Power Sources,2012,217:373-380
24 Liu L,Li Q,Dai J,et al.A facile strategy for the synthesis of guanidinium-functionalized polymer as alkaline anion exchange membrane with improved alkaline stability.J Membr Sci,2014,453:52-60
25 Zhang Q,Li S,Zhang S.A novel guanidinium grafted poly(aryl ether sulfone)for high-performance hydroxide exchange membranes.Chem Commun,2010,46:7495-7497
26 Kim D,Labouriau A,Guiver M,et al.Guanidinium-functionalized anion exchange polymer electrolytes via activated fluorophenylamine reaction.Chem Mater,2011,23:3795-3797
27 Kim D,Fujimoto C,Hibbs M,et al.Resonance stabilized perfluorinated ionomers for alkaline membrane fuel cells.Macromolecules,2013,46:7826-7833
28 Xue B,Dong X,Li Y,et al.Synthesis of novel guanidinium-based anion-exchange membranes with controlled microblock structures.JMembr Sci,2017,537:151-159
29 Qu C,Zhang H,Zhang F,et al.A high-performance anion exchange membrane based on bi-guanidinium bridged polysilsesquioxane for alkaline fuel cell application.J Mater Chem,2012,22:8203-8207
30 Chen Y,Tao Y,Wang J,et al.Comb-shaped guanidinium functionalized poly(ether sulfone)s for anion exchange membranes:Effects of the spacer types and lengths.J Polym Sci Part A Polym Chem,2017,55:1313-1320
31 Sajjada S,HongY,Liu F.Synthesis of guanidinium-based anion exchange membranes and their stability assessment.Polym Adv Technol,2014,25:108-116
32 Sherazi T,Zahoor S,Raza R,et al.Guanidine functionalized radiation induced grafted anion-exchange membranes for solid alkaline fuel cells.Int J Hydrog Energy,2015,40:786-796
33 Cheng J,Yang G,Zhang K,et al.Guanidimidazole-quanternized and cross-linked alkaline polymer electrolyte membrane for fuel cell application.J Membr Sci,2016,501:100-108
34 Mohanty A,Bae C.Mechanistic analysis of ammonium cation stability for alkaline exchange membrane fuel cells.J Mater Chem A,2014,2:17314-17320
35 Li W,Wang S,Zhang X,et al.Degradation of guanidinium-functionalized anion exchange membrane during alkaline environment.Int JHydrog Energy,2014,39:13710-13717
36 Fukui K.Role of frontier orbitals in chemical reactions.Science,1982,218:747-754
37 Pernpointner M,Hashmi A S K.Fully relativistic,comparative investigation of gold and platinum alkyne complexes of relevance for the catalysis of nucleophilic additions to alkynes.J Chem Theory Comput,2009,5:2717-2725