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{{Short description|Ion-exchange membrane specific for protons}}
{{Use dmy dates|date=August 2013}}
{{Use dmy dates|date=June 2024}}
A '''proton-exchange membrane''', or '''polymer-electrolyte membrane''' ('''PEM'''), is a [[Ion-exchange membranes|semipermeable membrane]] generally made from [[ionomer]]s and designed to [[proton conductor|conduct protons]] while acting as an electronic insulator and reactant barrier, e.g. to [[oxygen]] and [[hydrogen]] gas.<ref name="NasaTechBriefs">{{cite techreport | url=http://www.techbriefs.com/component/content/article/9-ntb/tech-briefs/physical-sciences/1440 | title=Alternative electrochemical systems for ozonation of water | accessdate=17 January 2015 | institution=[[NASA]] | date=20 March 2007 | work=[[NASA Tech Briefs]] | number=MSC-23045 }}</ref> This is their essential function when incorporated into a [[membrane electrode assembly]] (MEA) of a [[proton-exchange membrane fuel cell]] or of a [[Polymer electrolyte membrane electrolysis|proton-exchange membrane electrolyser]]: separation of reactants and transport of protons while blocking a direct electronic pathway through the membrane.
A '''proton-exchange membrane''', or '''polymer-electrolyte membrane''' ('''PEM'''), is a [[ion-exchange membrane|semipermeable membrane]] generally made from [[ionomer]]s and designed to [[proton conductor|conduct protons]] while acting as an electronic insulator and reactant barrier, e.g. to [[oxygen]] and [[hydrogen]] gas.<ref name="NasaTechBriefs">{{cite tech report | url=http://www.techbriefs.com/component/content/article/9-ntb/tech-briefs/physical-sciences/1440 | title=Alternative electrochemical systems for ozonation of water | access-date=17 January 2015 | institution=[[NASA]] | date=20 March 2007 | work=[[NASA Tech Briefs]] | number=MSC-23045 }}</ref> This is their essential function when incorporated into a [[membrane electrode assembly]] (MEA) of a [[proton-exchange membrane fuel cell]] or of a [[Polymer electrolyte membrane electrolysis|proton-exchange membrane electrolyser]]: separation of reactants and transport of protons while blocking a direct electronic pathway through the membrane.


PEMs can be made from either pure [[polymer]] membranes or from [[Composite material|composite]] membranes, where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is the [[fluoropolymer]] (PFSA)<ref>{{cite journal|url=http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/49_2_Philadelphia_10-04_1065.pdf |title=Novel inorganic/organic hybrid electrolyte membranes |author=Zhiwei Yang|year=2004 |volume=49 |issue=2 |pages=599 |journal=Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem.|display-authors=etal}}</ref> [[Nafion]], a [[DuPont]] product.<ref name="patent">{{Ref patent|country=US|number=5266421|status=patent|title=US Patent 5266421 – Enhanced membrane-electrode interface|pubdate=|gdate=2008-11-30|fdate=1992-05-12|pridate=|invent1=Townsend, Carl W.|invent2=Naselow, Arthur B.|assign1=[[Hughes Aircraft]]|assign2=|class=H01M8/10B2}}</ref> While Nafion is an ionomer with a perfluorinated backbone like [[Teflon]]<ref name = "Nafion">{{cite web |url=http://news.softpedia.com/news/New-Proton-Exchange-Membrane-Developed-74083.shtml |title=New Proton Exchange Membrane Developed – Nafion promises inexpensive fuel-cells |accessdate=2008-07-18 |author=Gabriel Gache |date=2007-12-17 |website= |publisher=[[Softpedia]]}}</ref>, there are many other structural motifs used to make ionomers for proton-exchange membranes. Many use polyaromatic polymers, while others use partially fluorinated polymers.
PEMs can be made from either pure [[polymer]] membranes or from [[Composite material|composite]] membranes, where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is the [[fluoropolymer]] (PFSA)<ref>{{cite journal|url=http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/49_2_Philadelphia_10-04_1065.pdf |title=Novel inorganic/organic hybrid electrolyte membranes |author=Zhiwei Yang|year=2004 |volume=49 |issue=2 |pages=599 |journal=Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem.|display-authors=etal}}</ref> [[Nafion]], a [[DuPont]] product.<ref name="patent">{{Cite patent|country=US|number=5266421|status=patent|title=Enhanced membrane-electrode interface|pubdate=|gdate=2008-11-30|fdate=1992-05-12|pridate=|invent1=Townsend, Carl W.|invent2=Naselow, Arthur B.|assign1=[[Hughes Aircraft]]}}</ref> While Nafion is an ionomer with a perfluorinated backbone like [[Teflon]],<ref name = "Nafion">{{cite web |url=http://news.softpedia.com/news/New-Proton-Exchange-Membrane-Developed-74083.shtml |title=New Proton Exchange Membrane Developed – Nafion promises inexpensive fuel-cells |access-date=2008-07-18 |author=Gabriel Gache |date=2007-12-17 |publisher=[[Softpedia]]}}</ref> there are many other structural motifs used to make ionomers for proton-exchange membranes. Many use polyaromatic polymers, while others use partially fluorinated polymers.


Proton-exchange membranes are primarily characterized by proton [[conductivity (electrolytic)|conductivity]] (σ), [[methanol]] permeability (''P''), and thermal stability.<ref name="VTech">{{cite web |url=http://www.mii.vt.edu/SURP/research/fcm.html |title=Research Topics for Materials and Processes for PEM Fuel Cells REU for 2008 |accessdate=2008-07-18 |author=Nakhiah Goulbourne |publisher=[[Virginia Polytechnic Institute and State University|Virginia Tech]] |url-status=dead |archiveurl=https://web.archive.org/web/20090227182952/http://www.mii.vt.edu/SURP/research/fcm.html |archivedate=27 February 2009 |df=dmy-all }}</ref>
Proton-exchange membranes are primarily characterized by proton [[conductivity (electrolytic)|conductivity]] (σ), [[methanol]] permeability (''P''), and thermal stability.<ref name="VTech">{{cite web |url=http://www.mii.vt.edu/SURP/research/fcm.html |title=Research Topics for Materials and Processes for PEM Fuel Cells REU for 2008 |access-date=2008-07-18 |author=Nakhiah Goulbourne |publisher=[[Virginia Polytechnic Institute and State University|Virginia Tech]] |url-status=dead |archive-url=https://web.archive.org/web/20090227182952/http://www.mii.vt.edu/SURP/research/fcm.html |archive-date=27 February 2009 }}</ref>


PEM fuel cells use a solid polymer membrane (a thin plastic film) as the electrolyte. This polymer is permeable to protons when it is saturated with water, but it does not conduct electrons.
PEM fuel cells use a solid polymer membrane (a thin plastic film) which is permeable to protons when it is saturated with water, but it does not conduct electrons.


==Fuel cell==
== History ==
[[File:Grubb_Niedrach_photo.jpg|thumb|274x274px|Leonard Niedrach (left) and Thomas Grubb (right), inventors of proton-exchange membrane technology.]]
Proton-exchange membrane fuel cells (PEMFCs) are believed to be the most promising type of fuel cell to act as the vehicular power source replacement for gasoline and diesel internal combustion engines. They are being considered for automobile applications because they typically have a low [[operating temperature]] (~80&nbsp;°C) and a rapid start-up time, including from frozen conditions. PEMFCs operate at 40–60% efficiency and can vary the output to match the demands. First used in the 1960s for the NASA [[Gemini program]], PEMFCs are currently being developed and demonstrated from ~100&nbsp;kW cars to a 59 MW power plant.{{citation needed|date=September 2017}}
Early proton-exchange membrane technology was developed in the early 1960s by Leonard Niedrach and Thomas Grubb, chemists working for the [[General Electric|General Electric Company]].<ref>{{Cite journal|last1=Grubb|first1=W. T.|last2=Niedrach|first2=L. W.|date=1960-02-01|title=Batteries with Solid Ion-Exchange Membrane Electrolytes: II . Low-Temperature Hydrogen-Oxygen Fuel Cells|url=https://iopscience.iop.org/article/10.1149/1.2427622/meta|journal=Journal of the Electrochemical Society|volume=107|issue=2|pages=131|doi=10.1149/1.2427622|issn=1945-7111}}</ref> Significant government resources were devoted to the study and development of these membranes for use in NASA's [[Project Gemini]] spaceflight program.<ref>{{Cite book|url=https://pubs.acs.org/isbn/9780841200487|title=Fuel Cell Systems|date=1969-01-01|publisher=AMERICAN CHEMICAL SOCIETY|isbn=978-0-8412-0048-7|editor-last=Young|editor-first=George J.|series=Advances in Chemistry|volume=47|location=WASHINGTON, D.C.|doi=10.1021/ba-1965-0047|editor-last2=Linden|editor-first2=Henry R.}}</ref> A number of technical problems led NASA to forego the use of proton-exchange membrane fuel cells in favor of batteries as a lower capacity but more reliable alternative for Gemini missions 1–4.<ref>{{Cite journal|date=April 1979|title=Barton C. Hacker and James M. Grimwood. On the Shoulders of Titans: A History of Project Gemini. Washington, D. C.: National Aeronautics and Space Administration. 1977. Pp. xx, 625. $19.00|url=http://dx.doi.org/10.1086/ahr/84.2.593|journal=The American Historical Review|doi=10.1086/ahr/84.2.593|issn=1937-5239}}</ref> An improved generation of General Electric's PEM fuel cell was used in all subsequent Gemini missions, but was abandoned for the subsequent [[Apollo program|Apollo]] missions.<ref name=":02">{{Cite web|title=Collecting the History of Proton Exchange Membrane Fuel Cells|url=https://americanhistory.si.edu/fuelcells/pem/pemmain.htm|access-date=2021-04-19|website=americanhistory.si.edu|publisher=Smithsonian Institution}}</ref> The fluorinated ionomer [[Nafion]], which is today the most widely utilized proton-exchange membrane material, was developed by [[DuPont (1802–2017)|DuPont]] plastics chemist Walther Grot. Grot also demonstrated its usefulness as an electrochemical separator membrane.<ref>{{Cite book|last=Grot|first=Walther|title=Fluorinated Ionomers – 2nd Edition|url=https://www.elsevier.com/books/fluorinated-ionomers/grot/978-1-4377-4457-6|access-date=2021-04-19|website=elsevier.com|date=15 July 2011 |publisher=William Andrew |isbn=978-1-4377-4457-6 }}</ref>


⚫
In 2014, [[Andre Geim]] of the [[University of Manchester]] published initial results on atom thick monolayers of [[graphene]] and [[boron nitride]] which allowed only protons to pass through the material, making them a potential replacement for fluorinated ionomers as a PEM material.<ref name="hu2014">
⚫
{{cite journal|author=Hu, S.|author2=Lozado-Hidalgo, M.|author3=Wang, F.C.|author4=Mishchenko, A.|author5=Schedin, F.|author6=Nair, R. R.|author7=Hill, E. W.|author8=Boukhvalov, D. W.|author9=Katsnelson, M. I.|author10=Dryfe, R. A. W.|author11=Grigorieva, I. V.|display-authors=3|date=26 November 2014|title=Proton transport through one atom thick crystals|journal=[[Nature (journal)|Nature]]|volume=516|issue=7530|pages=227–30|arxiv=1410.8724|bibcode=2014Natur.516..227H|doi=10.1038/nature14015|pmid=25470058|author12=Wu, H. A.|author13=Geim, A. K.|author13-link=Andre Geim|s2cid=4455321}}</ref><ref>{{cite journal|last1=Karnik|first1=Rohit N.|date=26 November 2014|title=Breakthrough for protons|journal=Nature|volume=516|issue=7530|pages=173–174|bibcode=2014Natur.516..173K|doi=10.1038/nature14074|pmid=25470064|s2cid=4390672|doi-access=free}}</ref>

==Fuel cell==
PEMFCs have some advantages over other types of fuel cells such as [[solid oxide fuel cell]]s (SOFC). PEMFCs operate at a lower temperature, are lighter and more compact, which makes them ideal for applications such as cars.
PEMFCs have some advantages over other types of fuel cells such as [[solid oxide fuel cell]]s (SOFC). PEMFCs operate at a lower temperature, are lighter and more compact, which makes them ideal for applications such as cars.
However, some disadvantages are: the ~80&nbsp;°C operating temperature is too low for cogeneration like in SOFCs, and that the electrolyte for PEMFCs must be water-saturated. However, some fuel-cell cars, including the [[Toyota Mirai]], operate without humidifiers, relying on rapid water generation and the high rate of back-diffusion through thin membranes to maintain the hydration of the membrane, as well as the ionomer in the catalyst layers.
However, some disadvantages are: the ~80&nbsp;°C operating temperature is too low for cogeneration like in SOFCs, and that the electrolyte for PEMFCs must be water-saturated. However, some fuel-cell cars, including the [[Toyota Mirai]], operate without humidifiers, relying on rapid water generation and the high rate of back-diffusion through thin membranes to maintain the hydration of the membrane, as well as the ionomer in the catalyst layers.


High-temperature PEMFCs operate between 100&nbsp;°C and 200&nbsp;°C, potentially offering benefits in electrode kinetics and heat management, and better tolerance to fuel impurities, particularly [[carbon monoxide|CO]] in reformate. These improvements potentially could lead to higher overall system efficiencies. However, these gains have yet to be realized, as the gold-standard perfluorinated sulfonic acid (PFSA) membranes lose function rapidly at 100&nbsp;°C and above if hydration drops below ~100%, and begin to creep in this temperature range, resulting in localized thinning and overall lower system lifetimes. As a result, new anhydrous proton conductors, such as protic organic ionic plastic crystals (POIPCs) and protic ionic liquids, are actively studied for the development of suitable PEMs.<ref>
High-temperature PEMFCs operate between 100&nbsp;°C and 200&nbsp;°C, potentially offering benefits in electrode kinetics and heat management, and better tolerance to fuel impurities, particularly [[carbon monoxide|CO]] in reformate. These improvements potentially could lead to higher overall system efficiencies. However, these gains have yet to be realized, as the gold-standard perfluorinated sulfonic acid (PFSA) membranes lose function rapidly at 100&nbsp;°C and above if hydration drops below ~100%, and begin to creep in this temperature range, resulting in localized thinning and overall lower system lifetimes. As a result, new anhydrous proton conductors, such as protic organic ionic plastic crystals (POIPCs) and [[protic ionic liquid]]s, are actively studied for the development of suitable PEMs.<ref>
{{cite journal
{{cite journal
|author1=Jiangshui Luo |author2=Annemette H. Jensen |author3=Neil R. Brooks |author4=Jeroen Sniekers |author5=Martin Knipper |author6=David Aili |author7=Qingfeng Li |author8=Bram Vanroy |author9=Michael Wübbenhorst |author10=Feng Yan |author11=Luc Van Meervelt |author12=Zhigang Shao |author13=Jianhua Fang |author14=Zheng-Hong Luo |author15=Dirk E. De Vos |author16=Koen Binnemans |author17=Jan Fransaer |year=2015
|author1=Jiangshui Luo |author2=Annemette H. Jensen |author3=Neil R. Brooks |author4=Jeroen Sniekers |author5=Martin Knipper |author6=David Aili |author7=Qingfeng Li |author8=Bram Vanroy |author9=Michael Wübbenhorst |author10=Feng Yan |author11=Luc Van Meervelt |author12=Zhigang Shao |author13=Jianhua Fang |author14=Zheng-Hong Luo |author15=Dirk E. De Vos |author16=Koen Binnemans |author17=Jan Fransaer |year=2015
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|issue=4 |pages=1276 |doi=10.1039/C4EE02280G
|issue=4 |pages=1276 |doi=10.1039/C4EE02280G
|url=http://orbit.dtu.dk/en/publications/124triazolium-perfluorobutanesulfonate-as-an-archetypal-pure-protic-organic-ionic-plastic-crystal-electrolyte-for-allsolidstate-fuel-cells(d5647472-6868-4873-ba5a-ddd28a3fe195).html }}</ref><ref>
|url=http://orbit.dtu.dk/en/publications/124triazolium-perfluorobutanesulfonate-as-an-archetypal-pure-protic-organic-ionic-plastic-crystal-electrolyte-for-allsolidstate-fuel-cells(d5647472-6868-4873-ba5a-ddd28a3fe195).html }}</ref><ref>
{{cite journal|author1=Jiangshui Luo, Olaf Conrad|author2=Ivo F. J. Vankelecom|year=2013|title=Imidazolium methanesulfonate as a high temperature proton conductor|url=https://lirias.kuleuven.be/bitstream/123456789/392330/2/JMCA_%20Imidazolium%20methanesulfonate%20as%20a%20high%20temperature%20proton%20conductor.pdf|journal=[[Journal of Materials Chemistry A]]|volume=1|issue=6|pages=2238|doi=10.1039/C2TA00713D}}</ref><ref>
{{cite journal
|author1=Jiangshui Luo, Olaf Conrad |author2=Ivo F. J. Vankelecom
|year=2013
|title=Imidazolium methanesulfonate as a high temperature proton conductor
|journal=[[Journal of Materials Chemistry A]]
|volume=1
|issue=6
|pages=2238
|doi=10.1039/C2TA00713D
}}</ref><ref>
{{cite journal
{{cite journal
|author1=Jiangshui Luo |author2=Jin Hu |author3=Wolfgang Saak |author4=Rüdiger Beckhaus |author5=Gunther Wittstock |author6=Ivo F. J. Vankelecom |author7=Carsten Agert |author8=Olaf Conrad |year=2011
|author1=Jiangshui Luo |author2=Jin Hu |author3=Wolfgang Saak |author4=Rüdiger Beckhaus |author5=Gunther Wittstock |author6=Ivo F. J. Vankelecom |author7=Carsten Agert |author8=Olaf Conrad |year=2011
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|issue=28 |pages=10426–10436
|issue=28 |pages=10426–10436
|doi=10.1039/C0JM04306K
|doi=10.1039/C0JM04306K
|url=https://lirias.kuleuven.be/bitstream/123456789/313759/2/JMC_%20Protic%20ionic%20liquid%20and%20ionic%20melts%20as%20high%20temperature%20PEMFC%20electrolytes.pdf }}</ref>
}}</ref>


The fuel for the PEMFC is hydrogen, and the charge carrier is the hydrogen ion (proton). At the anode, the hydrogen molecule is split into hydrogen ions (protons) and electrons. The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and produce electric power. Oxygen, usually in the form of air, is supplied to the cathode and combines with the electrons and the hydrogen ions to produce water. The reactions at the electrodes are as follows:
The fuel for the PEMFC is hydrogen, and the charge carrier is the hydrogen ion (proton). At the anode, the hydrogen molecule is split into hydrogen ions (protons) and electrons. The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and produce electric power. Oxygen, usually in the form of air, is supplied to the cathode and combines with the electrons and the hydrogen ions to produce water. The reactions at the electrodes are as follows:
Line 52: Line 49:
The theoretical exothermic potential is +1.23 V overall.
The theoretical exothermic potential is +1.23 V overall.


==Applications==
==Atomically thin material==
The primary application of proton-exchange membranes is in PEM fuel cells. These fuel cells have a wide variety of commercial and military applications including in the aerospace, automotive, and energy industries.<ref name=":02"/><ref>{{Cite web|title=Could This Hydrogen-Powered Drone Work?|url=http://www.popsci.com/could-hydrogen-fuel-cell-drone-work|access-date=2016-01-07|website=Popular Science|date=23 May 2015 }}</ref>
⚫
In 2014, [[Andre Geim]] of the [[University of Manchester]] published initial results on atom thick monolayers of [[graphene]] and [[boron nitride]] which allowed only protons to pass through the material.<ref name="hu2014">


Early PEM fuel cell applications were focused within the aerospace industry. The then-higher capacity of fuel cells compared to batteries made them ideal as NASA's Project Gemini began to target longer duration space missions than had previously been attempted.<ref name=":02" />
⚫
{{cite journal | title=Proton transport through one atom thick crystals | journal=[[Nature (journal)|Nature]] | doi=10.1038/nature14015 | date=26 November 2014 | author=Hu, S. | author2=Lozado-Hidalgo, M. | author3=Wang, F.C. | author4=Mishchenko, A. | author5=Schedin, F. | author6=Nair, R. R. | author7=Hill, E. W. | author8=Boukhvalov, D. W. | author9=Katsnelson, M. I. | author10=Dryfe, R. A. W. | author11=Grigorieva, I. V. | author12=Wu, H. A. | author13=Geim, A. K. | author13-link=Andre Geim | display-authors=3 | volume=516 | issue=7530 | pages=227–30 | arxiv=1410.8724 | bibcode=2014Natur.516..227H | pmid=25470058 }}</ref><ref>{{cite journal |last1=Karnik |first1=Rohit N. |title=Breakthrough for protons |journal=Nature |date=26 November 2014 |volume=516 |issue=7530 |pages=173–174 |doi=10.1038/nature14074|bibcode=2014Natur.516..173K }}</ref>


{{As of |2008}}, the automotive industry as well as personal and public power generation are the largest markets for proton-exchange membrane fuel cells.<ref>{{Cite journal|last1=Barbir|first1=F.|last2=Yazici|first2=S.|date=2008|title=Status and development of PEM fuel cell technology|journal=International Journal of Energy Research|volume=32|issue=5|pages=369–378|doi=10.1002/er.1371|s2cid=110367501 |issn=1099-114X|doi-access=free|bibcode=2008IJER...32..369B }}</ref> PEM fuel cells are popular in automotive applications due to their relatively low operating temperature and their ability to start up quickly even in below-freezing conditions.<ref name=":1">{{Cite journal|date=2019-04-23|title=Review on the research of hydrogen storage system fast refueling in fuel cell vehicle|url=https://www.sciencedirect.com/science/article/abs/pii/S0360319919308663|journal=International Journal of Hydrogen Energy|volume=44|issue=21|pages=10677–10693|doi=10.1016/j.ijhydene.2019.02.208|issn=0360-3199|last1=Li|first1=Mengxiao|last2=Bai|first2=Yunfeng|last3=Zhang|first3=Caizhi|last4=Song|first4=Yuxi|last5=Jiang|first5=Shangfeng|last6=Grouset|first6=Didier|last7=Zhang|first7=Mingjun|bibcode=2019IJHE...4410677L |s2cid=108785340 }}</ref> As of March 2019 there were 6,558 fuel cell vehicles on the road in the United States, with the [[Toyota Mirai]] being the most popular model.<ref>{{Cite web|title=Fact of the Month March 2019: There Are More Than 6,500 Fuel Cell Vehicles On the Road in the U.S.|url=https://www.energy.gov/eere/fuelcells/fact-month-march-2019-there-are-more-6500-fuel-cell-vehicles-road-us|access-date=2021-04-19|website=Energy.gov}}</ref> PEM fuel cells have seen successful implementation in other forms of heavy machinery as well, with [[Ballard Power Systems]] supplying [[forklift]]s based on the technology.<ref>{{Cite web|title=Material Handling – Fuel Cell Solutions {{!}} Ballard Power|url=https://www.ballard.com/markets/material-handling|access-date=2021-04-19|website=ballard.com}}</ref> The primary challenge facing automotive PEM technology is the safe and efficient storage of hydrogen, currently an area of high research activity.<ref name=":1" />
==Commercial applications==
PEM fuel cells have been used to power everything from cars to drones.<ref>{{Cite web|url=http://fuelcells.org/uploads/carchart.pdf|title=Fuel Cell Vehicles|date=|website=|accessdate=}}</ref><ref>{{Cite web|url=http://www.popsci.com/could-hydrogen-fuel-cell-drone-work|title=Could This Hydrogen-Powered Drone Work?|website=Popular Science|accessdate=2016-01-07}}</ref> 3,000 fuel cell cars will be sold or leased in 2016 globally, with 30,000 intended for 2017. [[Ballard Power Systems]] has developed a completely viable commercial market supplying [[forklift]]s.


[[Polymer electrolyte membrane electrolysis]] is a technique by which proton-exchange membranes are used to decompose water into hydrogen and oxygen gas.<ref>{{Cite journal|date=2013-04-22|title=A comprehensive review on PEM water electrolysis|url=https://www.sciencedirect.com/science/article/abs/pii/S0360319913002607|journal=International Journal of Hydrogen Energy|volume=38|issue=12|pages=4901–4934|doi=10.1016/j.ijhydene.2013.01.151|issn=0360-3199|last1=Carmo|first1=Marcelo|last2=Fritz|first2=David L.|last3=Mergel|first3=Jürgen|last4=Stolten|first4=Detlef|bibcode=2013IJHE...38.4901C }}</ref> The proton-exchange membrane allows for the separation of produced hydrogen from oxygen, allowing either product to be exploited as needed. This process has been used variously to generate hydrogen fuel and oxygen for life-support systems in vessels such as [[United States Navy|US]] and [[Royal Navy]] submarines.<ref name=":02" /> A recent example is the construction of a 20 MW [[Air Liquide]] PEM electrolyzer plant in Québec.<ref>{{cite web|date=25 February 2019|title=Air Liquide invests in the world's largest membrane-based electrolyzer to develop its carbon-free hydrogen production|url=https://www.newswire.ca/news-releases/air-liquide-invests-in-the-world-s-largest-membrane-based-electrolyzer-to-develop-its-carbon-free-hydrogen-production-892301297.html|access-date=28 August 2020|website=newswire.ca|publisher=Air Liquide}}</ref> Similar PEM-based devices are available for the industrial production of ozone.<ref>{{Cite patent|title=PEM (proton exchange membrane) low-voltage electrolysis ozone generating device|gdate=2011-05-16|url=https://patents.google.com/patent/CN202116659U/en}}</ref>
PEM is used in devices for [[hydrogen]] production for hydrogen water.
To prevent from production of [[ozone]] at the [[oxygen]] electrode this contact (of this electrode) to the water is 'out-sourced,' which does not produce oxygen as the usual [[electrolysis]] technique, and this does prevent production of ozone.{{citation needed|date=September 2019}}


==See also==
==See also==
Line 74: Line 69:
* [[Isotope electrochemistry]]
* [[Isotope electrochemistry]]
* [[Membrane electrode assembly]]
* [[Membrane electrode assembly]]
* [[Polymer electrolyte membrane electrolysis]]
* [[Proton exchange membrane electrolysis]]
* [[Roll-to-roll]]
* [[Roll-to-roll]]
{{div col end}}
{{div col end}}

Latest revision as of 03:45, 18 June 2024

A proton-exchange membrane, or polymer-electrolyte membrane (PEM), is a semipermeable membrane generally made from ionomers and designed to conduct protons while acting as an electronic insulator and reactant barrier, e.g. to oxygen and hydrogen gas.[1] This is their essential function when incorporated into a membrane electrode assembly (MEA) of a proton-exchange membrane fuel cell or of a proton-exchange membrane electrolyser: separation of reactants and transport of protons while blocking a direct electronic pathway through the membrane.

PEMs can be made from either pure polymer membranes or from composite membranes, where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is the fluoropolymer (PFSA)[2] Nafion, a DuPont product.[3] While Nafion is an ionomer with a perfluorinated backbone like Teflon,[4] there are many other structural motifs used to make ionomers for proton-exchange membranes. Many use polyaromatic polymers, while others use partially fluorinated polymers.

Proton-exchange membranes are primarily characterized by proton conductivity (σ), methanol permeability (P), and thermal stability.[5]

PEM fuel cells use a solid polymer membrane (a thin plastic film) which is permeable to protons when it is saturated with water, but it does not conduct electrons.

History

[edit]
Leonard Niedrach (left) and Thomas Grubb (right), inventors of proton-exchange membrane technology.

Early proton-exchange membrane technology was developed in the early 1960s by Leonard Niedrach and Thomas Grubb, chemists working for the General Electric Company.[6] Significant government resources were devoted to the study and development of these membranes for use in NASA's Project Gemini spaceflight program.[7] A number of technical problems led NASA to forego the use of proton-exchange membrane fuel cells in favor of batteries as a lower capacity but more reliable alternative for Gemini missions 1–4.[8] An improved generation of General Electric's PEM fuel cell was used in all subsequent Gemini missions, but was abandoned for the subsequent Apollo missions.[9] The fluorinated ionomer Nafion, which is today the most widely utilized proton-exchange membrane material, was developed by DuPont plastics chemist Walther Grot. Grot also demonstrated its usefulness as an electrochemical separator membrane.[10]

In 2014, Andre Geim of the University of Manchester published initial results on atom thick monolayers of graphene and boron nitride which allowed only protons to pass through the material, making them a potential replacement for fluorinated ionomers as a PEM material.[11][12]

Fuel cell

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PEMFCs have some advantages over other types of fuel cells such as solid oxide fuel cells (SOFC). PEMFCs operate at a lower temperature, are lighter and more compact, which makes them ideal for applications such as cars. However, some disadvantages are: the ~80 °C operating temperature is too low for cogeneration like in SOFCs, and that the electrolyte for PEMFCs must be water-saturated. However, some fuel-cell cars, including the Toyota Mirai, operate without humidifiers, relying on rapid water generation and the high rate of back-diffusion through thin membranes to maintain the hydration of the membrane, as well as the ionomer in the catalyst layers.

High-temperature PEMFCs operate between 100 °C and 200 °C, potentially offering benefits in electrode kinetics and heat management, and better tolerance to fuel impurities, particularly CO in reformate. These improvements potentially could lead to higher overall system efficiencies. However, these gains have yet to be realized, as the gold-standard perfluorinated sulfonic acid (PFSA) membranes lose function rapidly at 100 °C and above if hydration drops below ~100%, and begin to creep in this temperature range, resulting in localized thinning and overall lower system lifetimes. As a result, new anhydrous proton conductors, such as protic organic ionic plastic crystals (POIPCs) and protic ionic liquids, are actively studied for the development of suitable PEMs.[13][14][15]

The fuel for the PEMFC is hydrogen, and the charge carrier is the hydrogen ion (proton). At the anode, the hydrogen molecule is split into hydrogen ions (protons) and electrons. The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and produce electric power. Oxygen, usually in the form of air, is supplied to the cathode and combines with the electrons and the hydrogen ions to produce water. The reactions at the electrodes are as follows:

Anode reaction:
2H2 → 4H+ + 4e−
Cathode reaction:
O2 + 4H+ + 4e− → 2H2O
Overall cell reaction:
2H2 + O2 → 2H2O + heat + electrical energy

The theoretical exothermic potential is +1.23 V overall.

Applications

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The primary application of proton-exchange membranes is in PEM fuel cells. These fuel cells have a wide variety of commercial and military applications including in the aerospace, automotive, and energy industries.[9][16]

Early PEM fuel cell applications were focused within the aerospace industry. The then-higher capacity of fuel cells compared to batteries made them ideal as NASA's Project Gemini began to target longer duration space missions than had previously been attempted.[9]

As of 2008, the automotive industry as well as personal and public power generation are the largest markets for proton-exchange membrane fuel cells.[17] PEM fuel cells are popular in automotive applications due to their relatively low operating temperature and their ability to start up quickly even in below-freezing conditions.[18] As of March 2019 there were 6,558 fuel cell vehicles on the road in the United States, with the Toyota Mirai being the most popular model.[19] PEM fuel cells have seen successful implementation in other forms of heavy machinery as well, with Ballard Power Systems supplying forklifts based on the technology.[20] The primary challenge facing automotive PEM technology is the safe and efficient storage of hydrogen, currently an area of high research activity.[18]

Polymer electrolyte membrane electrolysis is a technique by which proton-exchange membranes are used to decompose water into hydrogen and oxygen gas.[21] The proton-exchange membrane allows for the separation of produced hydrogen from oxygen, allowing either product to be exploited as needed. This process has been used variously to generate hydrogen fuel and oxygen for life-support systems in vessels such as US and Royal Navy submarines.[9] A recent example is the construction of a 20 MW Air Liquide PEM electrolyzer plant in Québec.[22] Similar PEM-based devices are available for the industrial production of ozone.[23]

See also

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References

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  1. ^ Alternative electrochemical systems for ozonation of water. NASA Tech Briefs (Technical report). NASA. 20 March 2007. MSC-23045. Retrieved 17 January 2015.
  2. ^ Zhiwei Yang; et al. (2004). "Novel inorganic/organic hybrid electrolyte membranes" (PDF). Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 49 (2): 599.
  3. ^ US patent 5266421, Townsend, Carl W. & Naselow, Arthur B., "Enhanced membrane-electrode interface", issued 2008-11-30, assigned to Hughes Aircraft 
  4. ^ Gabriel Gache (17 December 2007). "New Proton Exchange Membrane Developed – Nafion promises inexpensive fuel-cells". Softpedia. Retrieved 18 July 2008.
  5. ^ Nakhiah Goulbourne. "Research Topics for Materials and Processes for PEM Fuel Cells REU for 2008". Virginia Tech. Archived from the original on 27 February 2009. Retrieved 18 July 2008.
  6. ^ Grubb, W. T.; Niedrach, L. W. (1 February 1960). "Batteries with Solid Ion-Exchange Membrane Electrolytes: II . Low-Temperature Hydrogen-Oxygen Fuel Cells". Journal of the Electrochemical Society. 107 (2): 131. doi:10.1149/1.2427622. ISSN 1945-7111.
  7. ^ Young, George J.; Linden, Henry R., eds. (1 January 1969). Fuel Cell Systems. Advances in Chemistry. Vol. 47. WASHINGTON, D.C.: AMERICAN CHEMICAL SOCIETY. doi:10.1021/ba-1965-0047. ISBN 978-0-8412-0048-7.
  8. ^ "Barton C. Hacker and James M. Grimwood. On the Shoulders of Titans: A History of Project Gemini. Washington, D. C.: National Aeronautics and Space Administration. 1977. Pp. xx, 625. $19.00". The American Historical Review. April 1979. doi:10.1086/ahr/84.2.593. ISSN 1937-5239.
  9. ^ a b c d "Collecting the History of Proton Exchange Membrane Fuel Cells". americanhistory.si.edu. Smithsonian Institution. Retrieved 19 April 2021.
  10. ^ Grot, Walther (15 July 2011). Fluorinated Ionomers – 2nd Edition. William Andrew. ISBN 978-1-4377-4457-6. Retrieved 19 April 2021. {{cite book}}: |website= ignored (help)
  11. ^ Hu, S.; Lozado-Hidalgo, M.; Wang, F.C.; et al. (26 November 2014). "Proton transport through one atom thick crystals". Nature. 516 (7530): 227–30. arXiv:1410.8724. Bibcode:2014Natur.516..227H. doi:10.1038/nature14015. PMID 25470058. S2CID 4455321.
  12. ^ Karnik, Rohit N. (26 November 2014). "Breakthrough for protons". Nature. 516 (7530): 173–174. Bibcode:2014Natur.516..173K. doi:10.1038/nature14074. PMID 25470064. S2CID 4390672.
  13. ^ Jiangshui Luo; Annemette H. Jensen; Neil R. Brooks; Jeroen Sniekers; Martin Knipper; David Aili; Qingfeng Li; Bram Vanroy; Michael Wübbenhorst; Feng Yan; Luc Van Meervelt; Zhigang Shao; Jianhua Fang; Zheng-Hong Luo; Dirk E. De Vos; Koen Binnemans; Jan Fransaer (2015). "1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells". Energy & Environmental Science. 8 (4): 1276. doi:10.1039/C4EE02280G.
  14. ^ Jiangshui Luo, Olaf Conrad; Ivo F. J. Vankelecom (2013). "Imidazolium methanesulfonate as a high temperature proton conductor" (PDF). Journal of Materials Chemistry A. 1 (6): 2238. doi:10.1039/C2TA00713D.
  15. ^ Jiangshui Luo; Jin Hu; Wolfgang Saak; Rüdiger Beckhaus; Gunther Wittstock; Ivo F. J. Vankelecom; Carsten Agert; Olaf Conrad (2011). "Protic ionic liquid and ionic melts prepared from methanesulfonic acid and 1H-1,2,4-triazole as high temperature PEMFC electrolytes" (PDF). Journal of Materials Chemistry. 21 (28): 10426–10436. doi:10.1039/C0JM04306K.
  16. ^ "Could This Hydrogen-Powered Drone Work?". Popular Science. 23 May 2015. Retrieved 7 January 2016.
  17. ^ Barbir, F.; Yazici, S. (2008). "Status and development of PEM fuel cell technology". International Journal of Energy Research. 32 (5): 369–378. Bibcode:2008IJER...32..369B. doi:10.1002/er.1371. ISSN 1099-114X. S2CID 110367501.
  18. ^ a b Li, Mengxiao; Bai, Yunfeng; Zhang, Caizhi; Song, Yuxi; Jiang, Shangfeng; Grouset, Didier; Zhang, Mingjun (23 April 2019). "Review on the research of hydrogen storage system fast refueling in fuel cell vehicle". International Journal of Hydrogen Energy. 44 (21): 10677–10693. Bibcode:2019IJHE...4410677L. doi:10.1016/j.ijhydene.2019.02.208. ISSN 0360-3199. S2CID 108785340.
  19. ^ "Fact of the Month March 2019: There Are More Than 6,500 Fuel Cell Vehicles On the Road in the U.S." Energy.gov. Retrieved 19 April 2021.
  20. ^ "Material Handling – Fuel Cell Solutions | Ballard Power". ballard.com. Retrieved 19 April 2021.
  21. ^ Carmo, Marcelo; Fritz, David L.; Mergel, Jürgen; Stolten, Detlef (22 April 2013). "A comprehensive review on PEM water electrolysis". International Journal of Hydrogen Energy. 38 (12): 4901–4934. Bibcode:2013IJHE...38.4901C. doi:10.1016/j.ijhydene.2013.01.151. ISSN 0360-3199.
  22. ^ "Air Liquide invests in the world's largest membrane-based electrolyzer to develop its carbon-free hydrogen production". newswire.ca. Air Liquide. 25 February 2019. Retrieved 28 August 2020.
  23. ^ [1], "PEM (proton exchange membrane) low-voltage electrolysis ozone generating device", issued 2011-05-16 
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