The effects of mercury on the performance of nickel/YSZ anode in a planar solid oxide fuel cell

This study was made to determine effects of mercury as a contaminant in coal syngas on the performance of a Ni/YSZ anode of a planar solid oxide fuel cell (SOFC). Anode supported SOFCs were operated with Hg-contaminated fuel gas at two different temperatures and at two different gas compositions. Significant modifications to the testing system were made to reduce the effects of stagnation layers. A reliable method of mercury delivery to the cell was designed, calibrated, and implemented prior to testing. A novel technique of area specific resistance (ASR) calculation using electrochemical impedance spectroscopy (EIS) was used, coupled with standard electrochemical techniques. The novel EIS technique for ASR analysis provided a reliable and repeatable method for determining cell degradation. Post-experimental materials analyses using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to determine the effects of mercury on SOFC performance. Electrochemical analyses coupled with material analyses demonstrated that mercury at concentrations as high as 1000 ppb had no discernable effect on normal cell performance. A novel method is proposed for computing cell degradation rate based on cell ASR that is much less current dependent than the present voltage-based method. Recommendations for future work include methods to improve SOFC test systems to obtain more reliable data by removing uncertainties in operational conditions.