Wikipedia

Proton-exchange membrane

Aproton-exchange membrane,orpolymer-electrolyte membrane(PEM), is asemipermeable membranegenerally made fromionomersand designed toconduct protonswhile acting as an electronic insulator and reactant barrier, e.g. tooxygenandhydrogengas.[1]This is their essential function when incorporated into amembrane electrode assembly(MEA) of aproton-exchange membrane fuel cellor of aproton-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 purepolymermembranes or fromcompositemembranes, where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is thefluoropolymer(PFSA)[2]Nafion,aDuPontproduct.[3]While Nafion is an ionomer with a perfluorinated backbone likeTeflon,[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 protonconductivity(σ),methanolpermeability (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

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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 theGeneral Electric Company.[6]Significant government resources were devoted to the study and development of these membranes for use in NASA'sProject Geminispaceflight 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 subsequentApollomissions.[9]The fluorinated ionomerNafion,which is today the most widely utilized proton-exchange membrane material, was developed byDuPontplastics chemist Walther Grot. Grot also demonstrated its usefulness as an electrochemical separator membrane.[10]

In 2014,Andre Geimof theUniversity of Manchesterpublished initial results on atom thick monolayers ofgrapheneandboron nitridewhich 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 assolid 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 theToyota 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, particularlyCOin 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) andprotic 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 theToyota Miraibeing the most popular model.[19]PEM fuel cells have seen successful implementation in other forms of heavy machinery as well, withBallard Power Systemssupplyingforkliftsbased 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 electrolysisis 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 asUSandRoyal Navysubmarines.[9]A recent example is the construction of a 20 MWAir LiquidePEM 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.Retrieved17 January2015.
  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 toHughes Aircraft
  4. ^Gabriel Gache (17 December 2007)."New Proton Exchange Membrane Developed – Nafion promises inexpensive fuel-cells".Softpedia.Retrieved18 July2008.
  5. ^Nakhiah Goulbourne."Research Topics for Materials and Processes for PEM Fuel Cells REU for 2008".Virginia Tech.Archived fromthe originalon 27 February 2009.Retrieved18 July2008.
  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.ISSN1945-7111.
  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.ISBN978-0-8412-0048-7.
  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.ISSN1937-5239.
  9. ^abcd"Collecting the History of Proton Exchange Membrane Fuel Cells".americanhistory.si.edu.Smithsonian Institution.Retrieved19 April2021.
  10. ^Grot, Walther (15 July 2011).Fluorinated Ionomers – 2nd Edition.William Andrew.ISBN978-1-4377-4457-6.Retrieved19 April2021.{{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.PMID25470058.S2CID4455321.
  12. ^Karnik, Rohit N. (26 November 2014)."Breakthrough for protons".Nature.516(7530):173–174.Bibcode:2014Natur.516..173K.doi:10.1038/nature14074.PMID25470064.S2CID4390672.
  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.Retrieved7 January2016.
  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.ISSN1099-114X.S2CID110367501.
  18. ^abLi, 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.ISSN0360-3199.S2CID108785340.
  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.Retrieved19 April2021.
  20. ^"Material Handling – Fuel Cell Solutions | Ballard Power".ballard.Retrieved19 April2021.
  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.ISSN0360-3199.
  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.Retrieved28 August2020.
  23. ^[1],"PEM (proton exchange membrane) low-voltage electrolysis ozone generating device", issued 2011-05-16
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