Editing Solid oxide fuel cell (section)

==Introduction==
Solid oxide fuel cells are a class of [[fuel cell]]s characterized by the use of a solid [[oxide]] material as the [[electrolyte]]. SOFCs use a solid oxide electrolyte to conduct negative oxygen ions from the [[cathode]] to the [[anode]]. The electrochemical oxidation of the [[hydrogen]], carbon monoxide or other organic intermediates by oxygen ions thus occurs on the anode side.<ref name="singh2021">{{cite journal |last1=Singh |first1=Mandeep |last2=Zappa |first2=Dario |last3=Comini |first3=Elisabetta |title=Solid oxide fuel cell: Decade of progress, future perspectives and challenges |journal=International Journal of Hydrogen Energy |date=August 2021 |volume=46 |issue=54 |pages=27643–27674 |doi=10.1016/j.ijhydene.2021.06.020|bibcode=2021IJHE...4627643S |s2cid=237909427 }}</ref><ref name="Boldrin2019">{{cite journal |last1=Boldrin |first1=Paul |last2=Brandon |first2=Nigel P. |title=Progress and outlook for solid oxide fuel cells for transportation applications |journal=Nature Catalysis |date=11 July 2019 |volume=2 |issue=7 |pages=571–577 |doi=10.1038/s41929-019-0310-y|hdl=10044/1/73325 |s2cid=199179410 |hdl-access=free }}</ref> More recently, proton-conducting SOFCs (PC-SOFC) are being developed which transport protons instead of oxygen ions through the electrolyte with the advantage of being able to be run at lower temperatures than traditional SOFCs.<ref name="gao2023">{{cite journal |last1=Gao |first1=Yang |last2=Zhang |first2=Mingming |last3=Fu |first3=Min |last4=Hu |first4=Wenjing |last5=Tong |first5=Hua |last6=Tao |first6=Zetian |title=A comprehensive review of recent progresses in cathode materials for Proton-conducting SOFCs |journal=Energy Reviews |date=September 2023 |volume=2 |issue=3 |pages=100038 |doi=10.1016/j.enrev.2023.100038|s2cid=259652830 |doi-access=free |bibcode=2023EnRev...200038G }}</ref><ref name="vignesh2023">{{cite journal |last1=Vignesh |first1=D. |last2=Rout |first2=Ela |title=Technological Challenges and Advancement in Proton Conductors: A Review |journal=Energy & Fuels |date=2 March 2023 |volume=37 |issue=5 |pages=3428–3469 |doi=10.1021/acs.energyfuels.2c03926|s2cid=256964689 |doi-access=free }}</ref>

They operate at very high temperatures, typically between 600 and 1,000&nbsp;°C.<ref name="singh2021" /><ref name="Boldrin2019" /> At these temperatures, SOFCs do not require expensive [[platinum group metals]] [[catalysts]],<ref name="Boldrin2019" /><ref name="wang2022">{{cite journal |last1=Wang |first1=Qi |last2=Fan |first2=Hui |last3=Xiao |first3=Yanfei |last4=Zhang |first4=Yihe |title=Applications and recent advances of rare earth in solid oxide fuel cells |journal=Journal of Rare Earths |date=November 2022 |volume=40 |issue=11 |pages=1668–1681 |doi=10.1016/j.jre.2021.09.003|bibcode=2022JREar..40.1668W |s2cid=240563264 }}</ref> as is currently necessary for lower temperature fuel cells such as [[proton-exchange membrane fuel cell|PEMFCs]], and are not vulnerable to carbon monoxide catalyst poisoning. However, vulnerability to [[sulfur]] poisoning<ref name="hagen2011">{{cite journal |last1=Hagen |first1=Anke |last2=Rasmussen |first2=Jens F.B. |last3=Thydén |first3=Karl |title=Durability of solid oxide fuel cells using sulfur containing fuels |journal=Journal of Power Sources |date=September 2011 |volume=196 |issue=17 |pages=7271–7276 |doi=10.1016/j.jpowsour.2011.02.053|bibcode=2011JPS...196.7271H }}</ref><ref name="Boldrin2019" /><ref name="kim2021">{{cite journal |last1=Kim |first1=Jun Hyuk |last2=Liu |first2=Mingfei |last3=Chen |first3=Yu |last4=Murphy |first4=Ryan |last5=Choi |first5=YongMan |last6=Liu |first6=Ying |last7=Liu |first7=Meilin |title=Understanding the Impact of Sulfur Poisoning on the Methane-Reforming Activity of a Solid Oxide Fuel Cell Anode |journal=ACS Catalysis |date=5 November 2021 |volume=11 |issue=21 |pages=13556–13566 |doi=10.1021/acscatal.1c02470}}</ref> has been widely observed and the sulfur must be removed before entering the cell. For fuels that are of lower quality, such as gasified biomass, coal, or [[biogas]], the fuel processing becomes increasingly complex and, consequently, more expensive. The gasification process, which transforms the raw material into a gaseous state suitable for fuel cells, can generate significant quantities of compounds like methane and toluene, as well as larger polyaromatic and short-chain hydrocarbon compounds. These substances can lead to carbon buildup in SOFCs. The expenses associated with reforming and desulfurization are comparable in magnitude to the cost of the fuel cell itself. These factors become especially critical for systems with lower power output or greater portability requirements.<ref name="Boldrin2016">{{cite journal |last1=Boldrin |first1=Paul |last2=Ruiz-Trejo |first2=Enrique |last3=Mermelstein |first3=Joshua |last4=Bermúdez Menéndez |first4=José Miguel |last5=Ramı́rez Reina |first5=Tomás |last6=Brandon |first6=Nigel P. |title=Strategies for Carbon and Sulfur Tolerant Solid Oxide Fuel Cell Materials, Incorporating Lessons from Heterogeneous Catalysis |journal=Chemical Reviews |date=23 November 2016 |volume=116 |issue=22 |pages=13633–13684 |doi=10.1021/acs.chemrev.6b00284|pmid=27933769 |doi-access=free |hdl=10044/1/41491 |hdl-access=free }}</ref>

Solid oxide fuel cells have a wide variety of applications, from use as auxiliary power units in vehicles to stationary power generation with outputs from 100 W to 2 MW. In 2009, Australian company, [[Ceramic Fuel Cells]] successfully achieved an efficiency of an SOFC device up to the previously theoretical mark of 60%.<ref>[http://www.cfcl.com.au/Assets/Files/20090219_CFCL_Announcement_60_percent_Efficiency.pdf Ceramic fuel cells achieves world-best 60% efficiency for its electricity generator units] {{webarchive|url=https://web.archive.org/web/20140603064840/http://cfcl.com.au/Assets/Files/20090219_CFCL_Announcement_60_percent_Efficiency.pdf |date=3 June 2014 }}. Ceramic Fuel Cells Limited. 19 February 2009</ref><ref name="e-collection.ethbib.ethz.ch">[http://e-collection.ethbib.ethz.ch/view/eth:41553 Electricity from wood through the combination of gasification and solid oxide fuel cells], Ph.D. Thesis by Florian Nagel, Swiss Federal Institute of Technology Zurich, 2008</ref> The higher operating temperature make SOFCs suitable candidates for application with [[heat engine]] [[energy recovery]] devices or [[combined heat and power]], which further increases overall [[fuel efficiency]].<ref>{{cite journal |last1=Radenahmad |first1=Nikdalila |last2=Azad |first2=Atia Tasfiah |last3=Saghir |first3=Muhammad |last4=Taweekun |first4=Juntakan |last5=Bakar |first5=Muhammad Saifullah Abu |last6=Reza |first6=Md Sumon |last7=Azad |first7=Abul Kalam |title=A review on biomass derived syngas for SOFC based combined heat and power application |journal=Renewable and Sustainable Energy Reviews |date=March 2020 |volume=119 |pages=109560 |doi=10.1016/j.rser.2019.109560|bibcode=2020RSERv.11909560R }}</ref>

Because of these high temperatures, light hydrocarbon fuels, such as methane, propane, and butane can be internally reformed within the anode.<ref>{{cite journal |last1=Xu |first1=Qidong |last2=Guo |first2=Zengjia |last3=Xia |first3=Lingchao |last4=He |first4=Qijiao |last5=Li |first5=Zheng |last6=Temitope Bello |first6=Idris |last7=Zheng |first7=Keqing |last8=Ni |first8=Meng |title=A comprehensive review of solid oxide fuel cells operating on various promising alternative fuels |journal=Energy Conversion and Management |date=February 2022 |volume=253 |pages=115175 |doi=10.1016/j.enconman.2021.115175|bibcode=2022ECM...25315175X |hdl=10397/97578 |hdl-access=free }}</ref> SOFCs can also be fueled by externally [[Fossil fuel reforming|reforming]] heavier hydrocarbons, such as gasoline, diesel, jet fuel (JP-8) or biofuels. Such reformates are mixtures of hydrogen, carbon monoxide, carbon dioxide, steam and methane, formed by reacting the hydrocarbon fuels with air or steam in a device upstream of the SOFC anode. SOFC power systems can increase efficiency by using the heat given off by the exothermic electrochemical oxidation within the fuel cell for endothermic [[steam reforming]] process. Additionally, solid fuels such as [[coal]] and [[biomass]] may be [[gasification|gasified]] to form [[syngas]] which is suitable for fueling SOFCs in [[Integrated Gasification Fuel Cell Cycle|integrated gasification fuel cell power cycles]].

[[Volumetric thermal expansion coefficient|Thermal expansion]] demands a uniform and well-regulated heating process at startup. SOFC stacks with planar geometry require on the order of an hour to be heated to operating temperature. [[Micro-tubular fuel cell design]]<ref>{{Cite journal|last=Sammes|first=N.M. |display-authors=etal |year=2005|title=Design and fabrication of a 100 W anode supported micro-tubular SOFC stack|journal=Journal of Power Sources|volume=145|issue=2 |pages=428–434|doi=10.1016/j.jpowsour.2005.01.079|bibcode=2005JPS...145..428S }}</ref><ref>{{Cite journal|last=Panthi|first=D. |display-authors=etal |year=2014|title=Micro-tubular solid oxide fuel cell based on a porous yttria-stabilized zirconia support|journal=Scientific Reports|volume=4|pages=5754|doi=10.1038/srep05754|pmid=25169166 |pmc=4148670 |bibcode=2014NatSR...4.5754P }}</ref> geometries promise much faster start up times, typically in the order of minutes.

Unlike most other types of fuel cells, SOFCs can have multiple geometries. The [[planar fuel cell design]] geometry is the typical sandwich type geometry employed by most types of fuel cells, where the electrolyte is sandwiched in between the electrodes. SOFCs can also be made in tubular geometries where either air or fuel is passed through the inside of the tube and the other gas is passed along the outside of the tube. The tubular design is advantageous because it is much easier to seal air from the fuel. The performance of the planar design is currently better than the performance of the tubular design, however, because the planar design has a lower resistance comparatively. Other geometries of SOFCs include [[modified planar fuel cell design]]s (MPC or MPSOFC), where a wave-like structure replaces the traditional flat configuration of the planar cell. Such designs are highly promising because they share the advantages of both planar cells (low resistance) and tubular cells.{{Citation needed|reason=Need citation for this modified planar design|date=May 2023}}