Tolerance Tests of Co-Feeding Cl₂ and H₂S Impurities in Biogas on a Ni-YSZ Anode-Supported Solid Oxide Fuel Cell

Biogas is a renewable resource which comes from numerous sources, such as biomass, manure, sewage, municipal waste, green waste and energy crops. It is a variable mixture of CH₄, CO₂, N₂ and other gases. Ni-YSZ cermet is commonly used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance and is cost effective. It can utilize not only hydrogen fuel, but also a clean synthesized biogas mixture of varying CH₄ and CO₂ concentrations with steam (H₂O) and air (O₂). However, trace impurities, such as H₂S, Cl₂, and F₂ in biogas may cause degradation of cell performance. In this work, Ni-CeO₂ coated Ni-YSZ anode-supported cells were exposed to two different compositions of synthesized biogases (biogas) with 100 ppm Cl₂ under a constant current load at 850°C. The electrochemical performance was evaluated periodically using standard electrochemical methods. 20 ppm H₂S impurity was also added to the fuel stream during the Cl₂ impurity testing and its effect was noted. Post-mortem analyses of the SOFC anode were performed using XRD, SEM and XPS. The results show that Cl₂ did not cause any electrochemical degradation of the cell during the 200 h test. However, after adding 20 ppm H₂S, the cell started to degrade and eventually lost all its performance. The experimental data showed that 100 ppm Cl₂ impurity in the fuel gas can postpone the degradation caused by addition of the H₂S impurity.