Editing Hydrogen (section)

=== Fuel ===
The potential for using hydrogen (H<sub>2</sub>)  as a fuel has been widely discussed. Hydrogen can be used in [[fuel cells]] to produce electricity,<ref>{{cite journal |doi=10.1155/2024/7271748 |title=A Recent Comprehensive Review of Fuel Cells: History, Types, and Applications |date=2024 |last1=Qasem |first1=Naef A. A. |last2=Abdulrahman |first2=Gubran A. Q. |journal=International Journal of Energy Research |issue=1 |doi-access=free |bibcode=2024IJER.202471748Q }}</ref> or burned to generate heat.<ref name="Lewis-2021">{{Cite journal |last=Lewis |first=Alastair C. |date=10 June 2021 |title=Optimising air quality co-benefits in a hydrogen economy: a case for hydrogen-specific standards for NO x emissions |journal=Environmental Science: Atmospheres |language=en |volume=1 |issue=5 |pages=201–207 |bibcode=2021ESAt....1..201L |doi=10.1039/D1EA00037C |doi-access=free}}{{Creative Commons text attribution notice|cc=by3|from this source=yes|url=|authors=|vrt=}}</ref> When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapor.<ref name="Lewis-2021" /> When burned, hydrogen produces relatively little pollution at the point of combustion, but can lead to thermal formation of harmful [[NOx|nitrogen oxides]].<ref name="Lewis-2021" />

If hydrogen is produced with low or zero greenhouse gas emissions ([[green hydrogen]]), it can play a significant role in decarbonizing energy systems where there are challenges and limitations to replacing fossil fuels with direct use of electricity.<ref name="IPCC-20222">{{Cite book |author=IPCC |author-link=IPCC |url=https://ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_FullReport.pdf |title=Climate Change 2022: Mitigation of Climate Change |publisher=Cambridge University Press (In Press) |year=2022 |isbn=9781009157926 |editor1-last=Shukla |editor1-first=P.R. |series=Contribution of Working Group III to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |place=Cambridge, UK and New York, NY, US |pages=91–92 |doi=10.1017/9781009157926 |ref={{harvid|IPCC AR6 WG3|2022}} |editor2-last=Skea |editor2-first=J. |editor3-last=Slade |editor3-first=R. |editor4-last=Al Khourdajie |editor4-first=A. |editor5-last=van Diemen |editor5-first=R. |editor6-last=McCollum |editor6-first=D. |editor7-last=Pathak |editor7-first=M. |editor8-last=Some |editor8-first=S. |editor9-last=Vyas |editor9-first=P. |display-editors=4 |editor10-first=R. |editor10-last=Fradera |editor11-first=M. |editor11-last=Belkacemi |editor12-first=A. |editor12-last=Hasija |editor13-first=G. |editor13-last=Lisboa |editor14-first=S. |editor14-last=Luz |editor15-first=J. |editor15-last=Malley}}</ref><ref name="Evans-2020" />

Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonization of industry alongside other technologies, such as [[electric arc furnace]]s for steelmaking.<ref>{{Cite web |last=Kjellberg-Motton |first=Brendan |date=2022-02-07 |title=Steel decarbonisation gathers speed {{!}} Argus Media |url=https://www.argusmedia.com/en//news/2299399-steel-decarbonisation-gathers-speed |access-date=2023-09-07 |website=www.argusmedia.com |language=en}}</ref> However, it is likely to play a larger role in providing industrial feedstock for cleaner production of ammonia and organic chemicals.<ref name="IPCC-2022">{{Cite book |author=IPCC |author-link=IPCC |url=https://ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_FullReport.pdf |title=Climate Change 2022: Mitigation of Climate Change |publisher=Cambridge University Press (In Press) |year=2022 |isbn=9781009157926 |editor1-last=Shukla |editor1-first=P.R. |series=Contribution of Working Group III to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |place=Cambridge, UK and New York, NY, US |pages=91–92 |doi=10.1017/9781009157926 |ref={{harvid|IPCC AR6 WG3|2022}} |editor2-last=Skea |editor2-first=J. |editor3-last=Slade |editor3-first=R. |editor4-last=Al Khourdajie |editor4-first=A. |editor5-last=van Diemen |editor5-first=R. |editor6-last=McCollum |editor6-first=D. |editor7-last=Pathak |editor7-first=M. |editor8-last=Some |editor8-first=S. |editor9-last=Vyas |editor9-first=P. |display-editors=4 |editor10-first=R. |editor10-last=Fradera |editor11-first=M. |editor11-last=Belkacemi |editor12-first=A. |editor12-last=Hasija |editor13-first=G. |editor13-last=Lisboa |editor14-first=S. |editor14-last=Luz |editor15-first=J. |editor15-last=Malley}}</ref> For example, in [[steelmaking]], hydrogen could function as a clean fuel and also as a low-carbon catalyst, replacing coal-derived [[Coke (fuel)|coke]] (carbon):<ref>{{Cite web |last1=Blank |first1=Thomas |last2=Molly |first2=Patrick |date=January 2020 |title=Hydrogen's Decarbonization Impact for Industry |url=https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf |url-status=live |archive-url=https://web.archive.org/web/20200922115313/https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf |archive-date=22 September 2020 |access-date= |publisher=[[Rocky Mountain Institute]] |pages=2, 7, 8}}</ref>
:{{chem2|2FeO  +  C -> 2Fe  +  CO2}}
:::vs
:{{chem2|FeO  +  H2 -> Fe  +  H2O}}
Hydrogen used to decarbonize transportation is likely to find its largest applications in shipping, aviation and, to a lesser extent, heavy goods vehicles, through the use of hydrogen-derived synthetic fuels such as [[Green ammonia|ammonia]] and [[Green methanol|methanol]] and fuel cell technology.<ref name="IPCC-2022" /> For light-duty vehicles including cars, hydrogen is far behind other [[alternative fuel vehicle]]s, especially compared with the rate of adoption of [[battery electric vehicles]], and may not play a significant role in future.<ref>{{Cite journal |last=Plötz |first=Patrick |date=2022-01-31 |title=Hydrogen technology is unlikely to play a major role in sustainable road transport |url=https://www.nature.com/articles/s41928-021-00706-6 |journal=Nature Electronics |language=en |volume=5 |issue=1 |pages=8–10 |doi=10.1038/s41928-021-00706-6 |s2cid=246465284 |issn=2520-1131}}</ref>

[[File:Shuttle Main Engine Test Firing cropped edited and reduced.jpg|thumb|[[Space Shuttle Main Engine]] burning hydrogen with oxygen, produces a nearly invisible flame at full thrust.|alt=A black inverted funnel with blue glow emerging from its opening.]]
[[Liquid hydrogen]] and [[liquid oxygen]] together serve as [[cryogenic propellant]]s in [[liquid-propellant rocket]]s, as in the [[RS-25|Space Shuttle main engines]]. [[NASA]] has investigated the use of [[rocket propellant]] made from atomic hydrogen, boron or carbon that is frozen into solid molecular hydrogen particles suspended in liquid helium. Upon warming, the mixture vaporizes to allow the atomic species to recombine, heating the mixture to high temperature.<ref>{{Cite web |url=https://ntrs.nasa.gov/api/citations/20030005922/downloads/20030005922.pdf |title=NASA/TM—2002-211915: Solid Hydrogen Experiments for Atomic Propellants |access-date=2 July 2021 |archive-date=9 July 2021 |archive-url=https://web.archive.org/web/20210709183557/https://ntrs.nasa.gov/api/citations/20030005922/downloads/20030005922.pdf |url-status=live }}</ref>

Hydrogen produced when there is a surplus of [[Variable renewable energy|variable renewable electricity]] could in principle be stored and later used to generate heat or to re-generate electricity.<ref>{{Cite journal |last1=Palys |first1=Matthew J. |last2=Daoutidis |first2=Prodromos |date=2020 |title=Using hydrogen and ammonia for renewable energy storage: A geographically comprehensive techno-economic study |journal=[[Computers & Chemical Engineering]] |volume=136 |pages=106785 |doi=10.1016/j.compchemeng.2020.106785 |issn=0098-1354 |doi-access=free}}</ref>  It can be further transformed into [[synthetic fuel]]s such as [[ammonia]] and [[methanol]].<ref>{{cite book |author=[[IRENA]] |url=https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2021/March/IRENA_World_Energy_Transitions_Outlook_2021.pdf |title=World Energy Transitions Outlook: 1.5°C Pathway |year=2021 |isbn=978-92-9260-334-2 |pages=12, 22 |archive-url=https://web.archive.org/web/20210611230855/https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2021/March/IRENA_World_Energy_Transitions_Outlook_2021.pdf |archive-date=11 June 2021 |url-status=live}}</ref> Disadvantages of hydrogen fuel include high costs of storage and distribution due to hydrogen's explosivity, its large volume compared to other fuels, and its tendency to make pipes brittle.<ref name="Griffiths-20212"/>