189:
ductility. Exchanging the counterion from hydroxide to hydrogen carbonate, carbonate, and chloride ions further enhances the strength and elastic modulus of the membranes. Narducci and colleagues concluded that the water uptake, related to the type of anion, plays a very important role for the mechanical properties. Zhang and colleagues prepared a series of robust and crosslinked poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) AEMs with chemically stable imidazolium cations through quaternization of C1, C3, C4-substituted imidazole and crosslinking them via "thiol-ene" chemistry. These crosslinked AEMs showed excellent film forming properties and exhibited a higher tensile strength owing to the increased entanglement interactions in the polymer chains which in turn increased the water up take. This strong relation between water uptake and mechanical properties mirrors the findings of
Narducci and colleagues. The findings of Zhang et al. suggest that the crosslinking of anion conductive materials with stable sterically-protected organic cations is an effective strategy to produce robust AEMs for use in alkaline fuel cells.
180:
used to measure these properties are very sensitive to the experimental procedure because the mechanical properties of polymers are heavily dependent on the nature of the environment such as the presence of water, organic solvents, oxygen, and temperature. Increasing the temperature generally results in a decrease of elastic modulus, a reduction of tensile strength, and an increase of ductility, assuming there is no modification of the microstructure. Near the glass transition temperature, very significant changes in mechanical properties is observed. Dynamic
Mechanical Analysis (DMA) is a widely used complimentary, characterization technique for measuring the mechanical properties of polymers including the storage modulus and loss modulus as functions of temperature.
92:
112:. Fuel is oxidized at anode and oxygen is reduced at cathode. At cathode, oxygen reduction produces hydroxides ions (OH) that migrate through the electrolyte towards the anode. At anode, hydroxide ions react with the fuel to produce water and electrons. Electrons go through the circuit producing current.
309:
Another challenge is achieving OH ion conductivity comparable to H conductivity observed in PEMFCs. Since the diffusion coefficient of OH ions is half that of H (in bulk water), a higher concentration of OH ions is needed to achieve similar results, which in turn needs higher ion-exchange capacity of
179:
The mechanical properties of anion-exchange membranes are relevant for use in electrochemical energy technologies such as polymer electrolyte membranes in fuel cells. Mechanical properties of polymers include the elastic modulus, tensile strength, and ductility. Traditional tensile stress-strain test
263:
is less than 0.07% and there is no precipitation on the electrodes in the absence of cations (K, Na). The absence of cations is, however, difficult to achieve, as most membranes are conditioned to functional hydroxide or bicarbonate forms out of their initial, chemically stable halogen form, and may
305:
when Ξ²-hydrogens are present and direct nucleophilic attack by OH ion at the cationic site. One approach towards improving the chemical stability towards
Hofmann elimination is to remove all Ξ²-hydrogens at the cationic site. All these degradation reactions limit the polymer backbone chemistries and
300:
used for PEMFCs, where an anion is covalently attached to the polymer and protons hop from one site to another. The challenge is to fabricate AEM with high OH ion conductivity and mechanical stability without chemical deterioration at elevated pH and temperatures. The main mechanisms of degradation
234:
systems have been developed using air as the oxidant source. In alkaline anion-exchange membrane fuel cell, aqueous KOH is replaced with a solid polymer electrolyte membrane, that can conduct hydroxide ions. This could overcome the problems of electrolyte leakage and carbonate precipitation, though
188:
One method of increasing the mechanical properties of polymers used for anion-exchange membranes (AEM) is substituting conventional ternary amine and anion exchange groups with grafted quaternary groups. These ionomers results in large storage and Young's moduli, a high tensile strength, and high
282:
has an advantage of easier storage and transportation and has higher volumetric energy density compared to hydrogen. Also, methanol crossover from anode to cathode is reduced in AAEMFCs compared to PEMFCs, due to the opposite direction of ion transport in the membrane, from cathode to anode. In
229:
precipitate on the electrodes. However, this effect has found to be mitigated by the removal of cationic counterions from the electrode, and carbonate formation has been found to be entirely reversible by several industrial and academic groups, most notably Varcoe. Low-cost
295:
The biggest challenge in developing AAEMFCs is the anion-exchange membrane (AEM). A typical AEM is composed of a polymer backbone with tethered cationic ion-exchange groups to facilitate the movement of free OH ions. This is the inverse of
823:
313:
Management of water in AEMFCs has also been shown to be a challenge. Recent research has shown that careful balancing of the humidity of the feed gases significantly improves fuel cell performance.
278:
The large majority of membranes/ionomer that have been developed are fully hydrocarbon, allowing for much easier catalyst recycling and lower fuel crossover.
209:
coming in through oxidant air stream and generated as by product from oxidation of methanol, if methanol is the fuel, reacts with electrolyte KOH forming CO
310:
the polymer. However, high ion-exchange capacity leads to excessive swelling of polymer on hydration and concomitant loss of mechanical properties.
729:
713:
656:
283:
addition, use of higher alcohols such as ethanol and propanol is possible in AAEMFCs, since anode potential in AAEMFCs is sufficient to oxidize
205:
and Space
Shuttle program generated electricity at nearly 70% efficiency using aqueous solution of KOH as an electrolyte. In that situation, CO
322:
412:
480:"Mechanical properties of anion exchange membranes by combination of tensile stressβstrain tests and dynamic mechanical analysis"
264:
significantly impact fuel cell performance by both competitively adsorbing to active sites and exerting
Helmholtz-layer effects.
590:
530:"Enhancement of the mechanical properties of anion exchange membranes with bulky imidazolium by "thiol-ene" crosslinking"
787:
Agel, E; Bouet, J.; Fauvarque, J.F (2001). "Characterization and use of anionic membranes for alkaline fuel cells".
327:
478:
Narducci, Riccardo; Chailan, J.-F.; Fahs, A.; Pasquini, Luca; Vona, Maria Luisa Di; Knauth, Philippe (2016).
56:
529:
528:
Zhang, Xiaojuan; Cao, Yejie; Zhang, Min; Huang, Yingda; Wang, Yiguang; Liu, Lei; Li, Nanwen (2020-02-15).
17:
707:
650:
726:
235:
still taking advantage of benefits of operating a fuel cell in an alkaline environment. In AAEMFCs, CO
796:
679:
491:
441:
862:
302:
77:
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557:
332:
268:
52:
695:
613:
591:"A carbon dioxide tolerant aqueouselectrolyte-free anion-exchange membrane alkaline fuel cell"
549:
507:
457:
408:
375:
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838:
824:"Importance of balancing membrane and electrode water in anion-exchange membrane fuel cells"
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precipitation, which can cause fuel (oxygen/hydrogen) transport problem during start-up.
800:
683:
495:
445:
430:"Viscoelastic Response of Nafion. Effects of Temperature and Hydration on Tensile Creep"
202:
808:
856:
575:
561:
773:
842:
822:
Omasta, T.J.; Wang, L.; Peng, X.; Lewis, C.A.; Varcoe, J.R.; Mustain, W.E. (2017).
271:, alkali anion-exchange membrane fuel cells also protect the electrode from solid
62:
Alkaline fuel cells (AFCs) are based on the transport of alkaline anions, usually
545:
746:
621:
81:
747:"Prospects for Alkaline Anion-Exchange Membranes in Low Temperature Fuel Cells"
553:
511:
461:
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63:
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Majsztrik, Paul W.; Bocarsly, Andrew B.; Benziger, Jay B. (2008-11-18).
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Anion
Exchange Membrane and Ionomer for Alkaline Membrane Fuel Cells
105:
91:
90:
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In an AAEMFC, the fuel, hydrogen or methanol, is supplied at the
198:
576:"Operating Method of Anion-Exchange Membrane-Type Fuel Cell"
393:
Knauth, Philippe; Di Vona, Maria Luisa, eds. (2012-01-27).
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the cations that can be incorporated for developing AEM.
76:, between the electrodes. Original AFCs used aqueous
354:"What are batteries, fuel cells, and supercapacitors?"
140:
Electrochemical reactions when methanol is the fuel:
115:
Electrochemical reactions when hydrogen is the fuel:
636:
634:
670:Mills, J. N.; McCrum, I. T.; Janik, M. J. (2014).
484:Journal of Polymer Science Part B: Polymer Physics
108:and oxygen through air, and water are supplied at
59:to separate the anode and cathode compartments.
45:hydroxide-exchange membrane fuel cells (HEMFCs)
193:Comparison with traditional alkaline fuel cell
8:
184:Methods of Increasing Mechanical Properties
88:membrane that transports hydroxide anions.
37:anion-exchange membrane fuel cells (AEMFCs)
95:Alkaline Anion-Exchange Membrane Fuel Cell
29:alkaline anion-exchange membrane fuel cell
18:Alkaline anion exchange membrane fuel cell
369:
745:Varcoe, J. R.; Slade, R. C. T. (2005).
344:
705:
648:
255:. The equilibrium concentration of CO
7:
589:Adams, L. A.; Varcoe, J. R. (2008).
523:
521:
473:
471:
323:Anion exchange membrane electrolysis
41:alkaline membrane fuel cells (AMFCs)
712:: CS1 maint: untitled periodical (
655:: CS1 maint: untitled periodical (
217:. Unfortunately as a consequence, K
25:
247:, which further dissociate to HCO
49:solid alkaline fuel cells (SAFCs)
352:Winter, M; Brodd, R. J. (2004).
197:The alkaline fuel cell used by
175:Measuring mechanical properties
843:10.1016/j.jpowsour.2017.05.006
1:
809:10.1016/s0378-7753(01)00759-5
396:Solid State Proton Conductors
84:. The AAEMFCs use instead a
641:Shen, P. K.; Xu, C. (2005).
546:10.1016/j.memsci.2019.117700
534:Journal of Membrane Science
239:reacts with water forming H
879:
732:December 7, 2008, at the
831:Journal of Power Sources
789:Journal of Power Sources
328:Proton-exchange membrane
267:In comparison, against
57:anion-exchange membrane
766:10.1002/fuce.200400045
672:Phys. Chem. Chem. Phys
610:10.1002/cssc.200700013
96:
405:10.1002/9781119962502
287:present in alcohols.
170:Mechanical properties
94:
801:2001JPS...101..267A
684:2014PCCP...1613699M
678:(27): 13699β13707.
496:2016JPoSB..54.1180N
446:2008MaMol..41.9849M
303:Hofmann elimination
78:potassium hydroxide
692:10.1039/c4cp00760c
504:10.1002/polb.24025
333:Alkaline fuel cell
269:alkaline fuel cell
97:
53:alkaline fuel cell
490:(12): 1180β1187.
454:10.1021/ma801811m
440:(24): 9849β9862.
371:10.1021/cr020730k
364:(10): 4245β4269.
35:), also known as
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147:OH + 6OH β CO
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795:(2): 267β274.
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760:(2): 187β200.
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627:on 2018-07-20.
604:(1β2): 79β81.
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166:O + 6e β 6OH
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137:O + 4e β 4OH
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201:in 1960s for
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129:At cathode: O
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143:At anode: CH
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80:(KOH) as an
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837:: 205β213.
598:ChemSusChem
118:At Anode: H
82:electrolyte
863:Fuel cells
754:Fuel Cells
645:: 149β179.
540:: 117700.
339:References
291:Challenges
122:+ 2OH β 2H
562:213381503
554:0376-7388
512:1099-0488
462:0024-9297
285:C-C bonds
273:carbonate
100:Mechanism
64:hydroxide
857:Category
774:18476566
730:Archived
700:24722828
618:18605667
380:15669155
317:See also
280:Methanol
155:O + 6e-
797:Bibcode
680:Bibcode
492:Bibcode
442:Bibcode
225:or KHCO
126:O + 2e
110:cathode
86:polymer
772:
698:
616:
560:
552:
510:
460:
411:
378:
298:Nafion
251:and CO
203:Apollo
33:AAEMFC
827:(PDF)
770:S2CID
750:(PDF)
625:(PDF)
594:(PDF)
558:S2CID
162:+ 3H
133:+ 2H
106:anode
47:, or
714:link
696:PMID
657:link
614:PMID
550:ISSN
508:ISSN
458:ISSN
409:ISBN
376:PMID
301:are
259:/HCO
213:/HCO
199:NASA
151:+ 5H
839:doi
835:375
805:doi
793:101
762:doi
688:doi
606:doi
542:doi
538:596
500:doi
450:doi
401:doi
366:doi
362:104
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243:CO
230:CO
221:CO
67:OH
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31:(
20:)
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