SOFC single cells fed by biogas: Experimental tests with trace contaminants

Biogas from biological treatments and from the waste degradation in landfills generally contains a wide range of trace impurities (e.g., sulphur compounds, siloxanes, halogens, tar compounds, etc.). This paper describes an experimental analysis performed with SOFC single cells fed by a synthetic gas polluted by H₂S, HCl, D4 and a mixture of H₂S + C₂Cl₄. The aim is to detect the threshold tolerance limit on different cell performance parameters. Results show how: hydrogen sulphide has a strong impact on the polarization losses due to the nickel sulphide formation on the electrode that causes a mass transfer resistance. Hydrogen chloride particularly limited the electrochemical processes. Octamethylcyclotetrasiloxane (D4) showed a high impact on SOFC performance even at ultra-low level (78-178 ppb(v)) as a consequence of the formation of silicon dioxide covering the anode porous sites. Sulphur added to C₂Cl₄, accelerated the deterioration of SOFC performance. In addition, current density variations and operating temperature are studied during sulphur poisoning. An opposite behaviour on SOFC performance was revealed by operating temperature and current density.