Cathodic reactions in general

The corrosion of a metal, a process of oxidation or loss of electrons, is supported by a cathodic reactant or oxidizing agent, which is reduced in performing the cathodic reaction. In general, the stronger the oxidizing reaction is, thermodynamically and kinetically, the greater the induced corrosion rate will be. 

For nongalvanized steel, cosmetic corrosion generally involves a cathodic delamination mechanism the surface under the paint becomes cathodic and the surface exposed in the hole becomes anodic. To slow down or prevent atmospheric corrosion, it is therefore important that the siuface treatment be a good cathodic inhibitor in the finished product. The phosphate layer increases corrosion resistance by limiting the available free surface for the cathodic reaction. In general, the activity of the free surface is further reduced by passivating posttreatments or by the deposition of amorphous phosphate films between the crystals. 

The majority of SOFC cathodes are based upon either LaMnOs or LaCoOa substituted with Sr on the A site and Fe on the B site. The rationale for using these materials is a result of the best compromise in properties for the cathodic reactions. In general, with higher temperature cells, such as those based on YSZ, the cathode functions as a triple phase boundary (TPB) material, where the chemical reactions between the electrode, electrolyte and gas phase take place at a limited area within the cathode structure (Figure 2.5). In this case the electrode material is functioning as an electronic conductor and oxygen reduction catalyst. For this case the Sr doped LaMnOs (LSM) is a suitable choice with conductivity of the order of 320 S cm at 800 for the... 

---