Editing Solid oxide fuel cell (section)

===Cathode===
The [[cathode]], or air [[electrode]], is a thin porous layer on the electrolyte where oxygen reduction takes place. The overall reaction is written in [[Kröger-Vink Notation]] as follows:

:<math> \frac{1}{2}\mathrm{O_2(g)} + 2\mathrm{e'} + {V}^{\bullet\bullet}_o \longrightarrow {O}^{\times}_o </math>
<!-- was: 1/2O<sub>2</sub>(g) + 2e' + V<sub>o</sub><sup>**</sup> -> O<sub>o</sub><sup>x</sup> -->

Cathode materials must be, at a minimum, electrically conductive. Currently, [[lanthanum strontium manganite]] (LSM) is the cathode material of choice for commercial use because of its compatibility with doped zirconia electrolytes. Mechanically, it has a similar coefficient of thermal expansion to YSZ and thus limits stress buildup because of CTE mismatch. Also, LSM has low levels of chemical reactivity with YSZ which extends the lifetime of the materials. Unfortunately, LSM is a poor ionic conductor, and so the electrochemically active reaction is limited to the [[triple phase boundary]] (TPB) where the electrolyte, air and electrode meet. LSM works well as a cathode at high temperatures, but its performance quickly falls as the operating temperature is lowered below 800&nbsp;°C. In order to increase the reaction zone beyond the TPB, a potential cathode material must be able to conduct both electrons and oxygen ions. Composite cathodes consisting of LSM YSZ have been used to increase this triple phase boundary length. Mixed ionic/electronic conducting (MIEC) ceramics, such as perovskite [[LSCF]], are also being researched for use in intermediate temperature SOFCs as they are more active and can make up for the increase in the activation energy of the reaction.<ref>{{Cite journal |last1=Shen |first1=F. |last2=Lu |first2=K. |date=August 2018 |title=Comparison of Different Perovskite Cathodes in Solid Oxide Fuel Cells |url=https://onlinelibrary.wiley.com/doi/10.1002/fuce.201800044 |journal=Fuel Cells |language=en |volume=18 |issue=4 |pages=457–465 |doi=10.1002/fuce.201800044 |s2cid=104669264 |issn=1615-6846|url-access=subscription }}</ref>