In Situ Optical Investigation of H 2 s Impact on Carbon Oxidation in Operating Solid Oxide Fuel Cells

While solid oxide fuel cells (SOFCs) promise efficient electricity production and high fuel flexibility, trace sulfur and chlorine constituents commonly found in desirable fuel sources such as syngas and biogas pose challenges. Sulfur poisoning is a well-established phenomenon that can lead to rapid loss of electrochemical performance in SOFCs that operate at high temperatures (650 – 800 °C). State-of-the-art Ni/YSZ (yttrium stabilized zirconia) anodes lose significant catalytic activity upon exposure to even ppm-levels of H 2 S, but details regarding how the catalyst degrades and the specific effects on electro-catalytic processes remain unclear. One approach to solving this shortcoming is to understand the degradation mechanisms through real time correlation of electrochemical performance with in situ , molecular specific observations. This current study uses infrared emission from the Ni/YSZ anode surface of an operating SOFC to simultaneously characterize 1) gas species using Fourier transform infrared emission spectroscopy (FTIRES) and 2) temperature changes using near infrared (NIR) thermal imaging. These data are collected with electrochemical potential when the SOFC is operated at 75% maximum current at 700 °C using CH 4 , with and without 170 ppm H 2 S added. In situ FTIRES measurements show that the CO 2 oxidation product and the CO electrochemical intermediate are suppressed when cell potential deteriorates with H 2 S present. Simultaneous NIR thermal imaging measurements of surface temperatures show that cooling also reflects evolving processes at the anode. After each trial, electrochemical oxidation of deposited carbon showed that H 2 S also hindered carbon accumulation. These results together have begun to provide direct insight into how sulfur poisoning affects electrochemical processes in SOFCs through correlations of electrochemical potential, surface temperature changes, and gas species at the anode.