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alkaline anion exchange membrane fuel cell wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 mechanism 2 mechanical properties toggle mechanical properties subsection 2 1 measuring mechanical properties 2 2 methods of increasing mechanical properties 3 comparison with traditional alkaline fuel cell toggle comparison with traditional alkaline fuel cell subsection 3 1 challenges 4 see also 5 references toggle the table of contents alkaline anion exchange membrane fuel cell 2 languages español français edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia an alkaline anion exchange membrane fuel cell aaemfc also known as anion exchange membrane fuel cells aemfcs alkaline membrane fuel cells amfcs hydroxide exchange membrane fuel cells hemfcs or solid alkaline fuel cells safcs is a type of alkaline fuel cell that uses an anion exchange membrane to separate the anode and cathode compartments alkaline fuel cells afcs are based on the transport of alkaline anions usually hydroxide oh between the electrodes original afcs used aqueous potassium hydroxide koh as an electrolyte the aaemfcs use instead a polymer membrane that transports hydroxide anions alkaline anion exchange membrane fuel cell mechanism edit in an aaemfc the fuel hydrogen or methanol is supplied at the anode and oxygen through air and water are supplied at cathode 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 1 electrochemical reactions when hydrogen is the fuel at anode h 2 2oh 2h 2 o 2e at cathode o 2 2h 2 o 4e 4oh electrochemical reactions when methanol is the fuel at anode ch 3 oh 6oh co 2 5h 2 o 6e at cathode 3 2o 2 3h 2 o 6e 6oh mechanical properties edit measuring mechanical properties edit 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 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 2 3 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 are 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 methods of increasing mechanical properties edit 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 4 these ionomers results in large storage and young s moduli a high tensile strength and high 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 4 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 5 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 5 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 comparison with traditional alkaline fuel cell edit the alkaline fuel cell used by nasa in 1960s for apollo and space shuttle program generated electricity at nearly 70 efficiency using aqueous solution of koh as an electrolyte in that situation co 2 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 3 2 hco 3 unfortunately as a consequence k 2 co 3 or khco 3 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 co 2 systems have been developed using air as the oxidant source 6 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 still taking advantage of benefits of operating a fuel cell in an alkaline environment in aaemfcs co 2 reacts with water forming h 2 co 3 which further dissociate to hco 3 and co 3 2 the equilibrium concentration of co 3 2 hco 3 is less than 0 07 and there is no precipitation on the electrodes in the absence of cations k na 7 8 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 significantly impact fuel cell performance by both competitively adsorbing to active sites and exerting helmholtz layer effects 9 in comparison against alkaline fuel cell alkali anion exchange membrane fuel cells also protect the electrode from solid carbonate precipitation which can cause fuel oxygen hydrogen transport problem during start up 10 the large majority of membranes ionomer that have been developed are fully hydrocarbon allowing for much easier catalyst recycling and lower fuel crossover methanol 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 addition use of higher alcohols such as ethanol and propanol is possible in aaemfcs since anode potential in aaemfcs is sufficient to oxidize c c bonds present in alcohols 11 8 challenges edit 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 nafion 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 are hofmann elimination when β 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 β hydrogens at the cationic site all these degradation reactions limit the polymer backbone chemistries and the cations that can be incorporated for developing aem 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 the polymer 12 however high ion exchange capacity leads to excessive swelling of polymer on hydration and concomitant loss of mechanical properties management of water in aemfcs has also been shown to be a challenge recent research has shown 13 that careful balancing of the humidity of the feed gases significantly improves fuel cell performance see also edit anion exchange membrane electrolysis proton exchange membrane references edit winter m brodd r j 2004 what are batteries fuel cells and supercapacitors chemical reviews 104 10 4245 4269 doi 10 1021 cr020730k pmid 15669155 knauth philippe di vona maria luisa eds 2012 01 27 solid state proton conductors doi 10 1002 9781119962502 isbn 978 1 119 96250 2 majsztrik paul w bocarsly andrew b benziger jay b 2008 11 18 viscoelastic response of nafion effects of temperature and hydration on tensile creep macromolecules 41 24 9849 9862 bibcode 2008mamol 41 9849m doi 10 1021 ma801811m issn 0024 9297 1 2 narducci riccardo chailan j f fahs a pasquini luca vona maria luisa di knauth philippe 2016 mechanical properties of anion exchange membranes by combination of tensile stress strain tests and dynamic mechanical analysis journal of polymer science part b polymer physics 54 12 1180 1187 bibcode 2016jposb 54 1180n doi 10 1002 polb 24025 issn 1099 0488 1 2 zhang xiaojuan cao yejie zhang min huang yingda wang yiguang liu lei li nanwen 2020 02 15 enhancement of the mechanical properties of anion exchange membranes with bulky imidazolium by thiol ene crosslinking journal of membrane science 596 117700 doi 10 1016 j memsci 2019 117700 issn 0376 7388 s2cid 213381503 operating method of anion exchange membrane type fuel cell adams l a varcoe j r 2008 a carbon dioxide tolerant aqueouselectrolyte free anion exchange membrane alkaline fuel cell pdf chemsuschem 1 1 2 79 81 doi 10 1002 cssc 200700013 pmid 18605667 archived from the original pdf on 2018 07 20 1 2 shen p k xu c 2005 adv fuel cells 149 179 cite journal cs1 maint untitled periodical link mills j n mccrum i t janik m j 2014 phys chem chem phys 16 27 13699 13707 bibcode 2014pccp 1613699m doi 10 1039 c4cp00760c pmid 24722828 cite journal cs1 maint untitled periodical link anion exchange membrane and ionomer for alkaline membrane fuel cells archived december 7 2008 at the wayback machine varcoe j r slade r c t 2005 prospects for alkaline anion exchange membranes in low temperature fuel cells pdf fuel cells 5 2 187 200 doi 10 1002 fuce 200400045 s2cid 18476566 agel e bouet j fauvarque j f 2001 characterization and use of anionic membranes for alkaline fuel cells journal of power sources 101 2 267 274 bibcode 2001jps 101 267a doi 10 1016 s0378 7753 01 00759 5 omasta t j wang l peng x lewis c a varcoe j r mustain w e 2017 importance of balancing membrane and electrode water in anion exchange membrane fuel cells pdf journal of power sources 375 205 213 doi 10 1016 j jpowsour 2017 05 006 retrieved from https en wikipedia org w index php title alkaline_anion exchange_membrane_fuel_cell oldid 1334141405 category fuel cells hidden categories cs1 maint untitled periodical webarchive template wayback links this page was last edited on 21 january 2026 at 20 13 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents alkaline anion exchange membrane fuel cell 2 languages add topic