Editing Fuel cell (section)

====Proton-exchange membrane fuel cell design issues====
; Cost: In 2013, the Department of Energy estimated that 80&nbsp;kW automotive fuel cell system costs of {{USD|67}} per kilowatt could be achieved, assuming volume production of 100,000 automotive units per year and {{USD|55}} per kilowatt could be achieved, assuming volume production of 500,000 units per year.<ref>
Spendelow, Jacob and Jason Marcinkoski. [http://www.hydrogen.energy.gov/pdfs/13012_fuel_cell_system_cost_2013.pdf "Fuel Cell System Cost – 2013"] {{webarchive|url=https://web.archive.org/web/20131202225059/http://www.hydrogen.energy.gov/pdfs/13012_fuel_cell_system_cost_2013.pdf |date= 2 December 2013 }}, DOE Fuel Cell Technologies Office, 16 October 2013 ([https://web.archive.org/web/20131202225059/http://www.hydrogen.energy.gov/pdfs/13012_fuel_cell_system_cost_2013.pdf archived version])
</ref> Many companies are working on techniques to reduce cost in a variety of ways including reducing the amount of platinum needed in each individual cell. [[Ballard Power Systems]] has experimented with a catalyst enhanced with carbon silk, which allows a 30% reduction (1.0–0.7&nbsp;mg/cm<sup>2</sup>) in platinum usage without reduction in performance.<ref>
{{Cite news
 | title = Ballard Power Systems: Commercially Viable Fuel Cell Stack Technology Ready by 2010
 | date = 29 March 2005
 | url = http://www.fuelcellsworks.com/Supppage2336.html
 | access-date = 2007-05-27
 | archive-url = https://web.archive.org/web/20070927050617/http://www.fuelcellsworks.com/Supppage2336.html
 | archive-date = 27 September 2007
 | url-status=dead
}}</ref> [[Monash University]], [[Melbourne]] uses [[poly(3,4-ethylenedioxythiophene)|PEDOT]] as a [[cathode]].<ref name="Online">
{{cite web
 |last=Online |first=Science
 |url=http://www.abc.net.au/news/stories/2008/08/02/2322139.htm
 |archive-url=https://web.archive.org/web/20080806174903/http://www.abc.net.au/news/stories/2008/08/02/2322139.htm
 |url-status=dead
 |archive-date=6 August 2008
 |title=2008 – Cathodes in fuel cells
 |publisher=Abc.net.au
 |date=2 August 2008
 |access-date=2009-09-21
}}</ref> A 2011-published study<ref>
{{cite journal
 | doi=10.1021/ja1112904
 | pmid=21413707
 | volume=133 | issue=14
 | title=Polyelectrolyte Functionalized Carbon Nanotubes as Efficient Metal-free Electrocatalysts for Oxygen Reduction
 | journal=Journal of the American Chemical Society
 | pages=5182–5185
 | last1 = Wang | first1 = Shuangyin
 | s2cid=207063759
 | year=2011
 | bibcode=2011JAChS.133.5182W
 }}</ref> documented the first metal-free electrocatalyst using relatively inexpensive doped [[carbon nanotube]]s, which are less than 1% the cost of platinum and are of equal or superior performance. A recently published article demonstrated how the environmental burdens change when using carbon nanotubes as carbon substrate for platinum.<ref>
{{cite journal
 |last1=Notter|first1=Dominic A.
 |last2=Kouravelou|first2=Katerina
 |last3=Karachalios|first3=Theodoros
 |last4=Daletou|first4=Maria K.
 |last5=Haberland|first5=Nara Tudela
 |title=Life cycle assessment of PEM FC applications: electric mobility and μ-CHP
 |journal=Energy Environ. Sci.
 |date=2015
 |volume=8|issue=7|pages=1969–1985
 |doi=10.1039/C5EE01082A
|bibcode=2015EnEnS...8.1969N
 }}</ref>
; Water and air management<ref>{{cite web|url=http://www.ika.rwth-aachen.de/r2h/index.php/Water_and_Air_Management_for_Fuel_Cells |title=Water_and_Air_Management |publisher=Ika.rwth-aachen.de |access-date=2009-09-21 |url-status=dead |archive-url=https://web.archive.org/web/20090114182615/http://www.ika.rwth-aachen.de/r2h/index.php/Water_and_Air_Management_for_Fuel_Cells |archive-date=14 January 2009}}</ref><ref>{{Cite journal|last1=Andersson|first1=M.|last2=Beale|first2=S. B.|last3=Espinoza|first3=M.|last4=Wu|first4=Z.|last5=Lehnert|first5=W.|date=2016-10-15|title=A review of cell-scale multiphase flow modeling, including water management, in polymer electrolyte fuel cells|journal=Applied Energy|volume=180|pages=757–778|doi=10.1016/j.apenergy.2016.08.010|bibcode=2016ApEn..180..757A }}</ref> (in PEMFCs): In this type of fuel cell, the membrane must be hydrated, requiring water to be evaporated at precisely the same rate that it is produced. If water is evaporated too quickly, the membrane dries, the resistance across it increases, and eventually, it will crack, creating a gas "short circuit" where hydrogen and oxygen combine directly, generating heat that will damage the fuel cell. If the water is evaporated too slowly, the electrodes will flood, preventing the reactants from reaching the catalyst and stopping the reaction. Methods to manage water in cells are being developed like [[electroosmotic pump]]s focusing on flow control. Just as in a combustion engine, a steady ratio between the reactant and oxygen is necessary to keep the fuel cell operating efficiently.
; Temperature management: The same temperature must be maintained throughout the cell in order to prevent destruction of the cell through [[thermal loading]]. This is particularly challenging as the 2H<sub>2</sub> + O<sub>2</sub> → 2H<sub>2</sub>O reaction is highly exothermic, so a large quantity of heat is generated within the fuel cell.
; Durability, [[service life]], and special requirements for some type of cells: [[Stationary fuel cell applications]] typically require more than 40,000 hours of reliable operation at a temperature of {{convert|-35|to|40|C|F}}, while automotive fuel cells require a 5,000-hour lifespan (the equivalent of {{convert|150000|miles|km|abbr=on|sigfig=2|order=flip|disp=or}}) under extreme temperatures. Current [[service life]] is 2,500 hours (about {{convert|75,000|mi|km|abbr=on|sigfig=2|order=flip|disp=or}}).<ref>{{cite web |url=http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/accomplishments.pdf |title=Progress and Accomplishments in Hydrogen and Fuel Cells |access-date=2015-05-16 |url-status=dead |archive-url=https://web.archive.org/web/20151123185414/http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/accomplishments.pdf |archive-date=23 November 2015}}</ref> Automotive engines must also be able to start reliably at {{convert|-30|°C|°F|abbr=on}} and have a high power-to-volume ratio (typically 2.5&nbsp;kW/L).
; Limited [[carbon monoxide]] tolerance of some (non-PEDOT) cathodes.<ref name=WGS />