Corrosion Susceptibility of Austenitic Stainless Steels in Direct Carbon Fuel Cell

Abstract

The direct carbon fuel cell (DCFC) is a future energy technology which is an efficient process for electrical energy generation from carbon-based sources. This technology has an extremely high theoretical efficiency due to favourable thermodynamics of the electro-oxidation reactions in the process. However, several technical challenges exist which must be addressed before the technology can be commercialized. One of the challenges is the corrosion of metal parts in the cell which limits the service life of the unit. In recent year, research on the development of new alloys and surface engineering have been done to address the corrosion issues in molten carbonate fuel cells. However, the literature on the corrosion behaviour of metals in a slurry system (coal + carbonate) is limited. Austenitic stainless steels are known for their high temperature corrosion resistance and excellent mechanical properties. In this work, the corrosion susceptibility of two types of austenitic stainless steels, i.e. 316L (16 wt.% Cr and 10wt. % Ni) and 235 MA (21 wt.% Cr and 11 wt.% Ni) were compared for fuel cell tank body application. The corrosion behaviour of the two stainless steels were evaluated in a slurry, which contained 20 wt% coal and 80 wt% ternary-eutectic (Li2CO3: 43.5 mol%, Na2CO3: 31.5 mol%, and K2CO3: 25.0 mol%), with nitrogen as a sweep gas at 800⁰C was examined for a 30-day period. The results indicate that the weight gain (due to corrosion product build-up) for both the stainless steels was marginal after 7 day exposure, i.e., 0.4% and 0.5% for 316L and 253 MA, respectively. However, after 30 days exposure, the weight gain increased to 0.98% for 316L, whereas for 253MA the weight gain remained at ~ 0.5%. Thus, the study suggest that 235 MA stainless steel is superior to 316L stainless steel in the coal-carbonate slurry environment. The corrosion mechanisms of the stainless steels will be discussed in the presentation.