Sulfur diffusion of hydrogen sulfide contaminants to cathode in a micro-tubular solid oxide fuel cell

Abstract

The contamination effect of hydrogen sulfide on micro-tubular solid oxide fuel cells was investigated using various electrochemical techniques. The cells, mechanically supported by cupper tube, were provided by National Metal and Materials Technology Center, and they contain the electrode materials of nickel and yttria stabilized zirconia cermet for anode and lanthanum strontium manganate for cathode. Pure hydrogen and hydrogen gas containing diluted hydrogen sulfide were repeatedly switched for the anode feed at the constant cell voltage of 0.9 V. Exposure times of 30 and 60 min were applied to study the effects of the poisoning interval. Then, the obtained results were analyzed. Herein, we reported two effects that had not been reported previously: the poisoning interval effect on the same hydrogen sulfide dosage and the poisoning sulfur-transport effect to the cathode surface. In the same dosage experiment, the recovery process was required before complete adsorption of sulfur species, and it supported not to fully block active sites of hydrogen adsorption and oxidation, and thus it would expand a cell lifespan on the contamination. In the analysis, different contamination steps between short and long term exposure time were presented, and thermodynamic parameters were calculated. Also, transport of elemental sulfur from the anode to the cathode surface was presented using the energy dispersive X-ray spectroscopy technique. The results appear to be strong evidence for the transport of sulfur from anode to cathode, and this means that the effect of sulfur diffusion to the cathode should be considered one major reason for performance degradation. This paper provides additional possible reasons regarding the performance degradation on hydrogen sulfide contamination, and serves as a guide to overcome the barrier of the sulfur contamination.