Nitridation and corrosion behavior of porous 430L stainless steel substrate under direct ammonia exposure

Metal-supported solid oxide fuel cells (M-SOFC) possess advantages such as high mechanical strength, high toughness, good thermal conductivity, and low cost compared to traditional ceramic-supported solid oxide fuel cells, making them widely studied as a new generation of clean energy devices. When fueled with liquid ammonia, which has been recognized as a clean hydrogen carrier with a much higher volumetric energy density than compressed hydrogen, the applications of M-SOFC can be further extended such as providing continuous power source for range-extended electric vehicle. Among reported metal supports, 430L stainless steel has been considered as one of the most affordable and promising materials for M-SOFC. However, we find that when porous 430L substrate is directly exposed to non-cracked ammonia fuel, much severer corrosion and damage than dense substrate are observed, particularly at 600 °C which coincidentally fits well with desired M-SOFC working temperature imposing significant challenges for the application of 430L or other stainless steels containing Cr and Fe as supports for M-SOFC. It is found that Fe, Cr, and Ni behave quite differently at tested temperatures, and porous 430L samples show fracture as soon as after being exposed to ammonia gas at 500 °C for 10 h and at 600 °C for 1 h. Our results thus suggest that cracking of ammonia either in-situ or externally is necessary for the use of 430L substrate in M-SOFC applications.