Development of sulfur tolerant anode for solid oxide fuel cells

• Main Author: Bek, Yong Joo.
• Other Authors: Chan Siew Hwa
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Alternative, renewable energy sources
• Online Access: http://hdl.handle.net/10356/16195
• Institution: Nanyang Technological University

Fuel cells are energy conversion devices that operate by converting the chemical energy stored inside appropriate fuels into electrical energy. In particular, Solid Oxide Fuel Cells (SOFCs) are a type of fuel cell that has unique characteristics that make them outstanding candidates for use in future power generation systems. They have good fuel flexibility, provide high quality power and are relatively clean running when compared to traditional heat engines. Despite their good fuel flexibility, SOFCs can be poisoned by certain substances. Hydrogen sulfide (H2S) in particular, is relatively common in most industrial fuels and poisons the anodes of fuel cells, causing performance drops or even anode delamination. H2S can be found in industrial fuels such as coal syngas, natural gas or even more „exotic‟ fuels such as biogas. Fuel purification, whilst not impossible, adds to the cost and complexity of fuel cell power systems, reducing their utility as well as attractiveness. To counter this problem, a number of sulfur tolerant anode materials have already been developed and tested to date. The work that remains then is to optimise and improve such materials so that they can eventually achieve commercial use. Of all the materials developed, one that shows particular promise is Strontium - doped Lanthanum Vanadate (LSV). Not only is LSV largely resistant to sulfur poisoning, it is also able to oxidise H2S, transforming H2S contained in the fuel feed from a useless poison into a potential fuel, thus allowing for increased electrical generation capability. Fuel cells equipped with anodes fabricated from LSV were electrochemically tested in a variety of fuels: pure H2, 100 ppm H2S balanced with H2 and 1000 ppm H2S balanced with CH4. The cells fabricated were tested over a temperature range of 800°C - 950°C. 60% LSV and 40% YSZ (Yttria –Stabilised Zirconia) was found to be the anode composition with the best performance, displaying stable operation and providing a maximum current density of 1.0 A/cm2 at voltage of 0.36V whilst operating at 950°C in 100ppm of H2S balanced with H2. 50 % LSV and 50% YSZ anodes also provided stable albeit poorer performance in sulfur containing fuels whilst the anodes with a composition of 70% LSV and 30% YSZ fared the worst, providing abysmal and unstable electrochemical performance in sulfur containing fuels. The results suggest that anodes with composition of LSV 60% YSZ 40% are stable whilst operating in sulfur contaminated environments and are more preferentially active towards the oxidation of H2S