|< FEBRUARY >||< 2018 >|
Venue: Room G114, Merchant Marine College
Speaker: Dr. Xingbo Liu, West Virginia University,
Solid Oxide Fuel Cells (SOFCs) is one of the promising alternative technologies for inefficient coal combustion for power generation, which can potentially operate on syngas obtained from coal. The main advantages of SOFCs are high overall plant efficiency (when the waste heat is used for bottoming cycles) and suitability for carbon sequestration. However there are still some unresolved problems with performance durability of these devices when operating on coal syngas, which inherently has some undesirable contaminants such as sulfur and phosphorus compounds.
At anode side, the most important issues are (1) understanding the effects of impurities on the performance and microstructural degradation of Ni-YSZ anodes, and (2) developing impurity-tolerant anodes. I will present our investigation on effect of phosphorous and sulfur on both Ni-YSZ and perovskite anodes and our attempts to develop S-tolerant anode. The sulfur tolerance introduced by LaxCe1-xO2 coating has been tested with MSRI cells by using Pt paste and nickel mesh on the anode as current collector. The degradation for the impregnated MSRI cell was postponed and the degradation degree after H2S attack was also alleviated.
At cathode side, our approaches are to develop electrochemical models to simulate the kinetics of oxygen reduction and reaction (ORR) and to improve the cathode performance by employing infiltration method. Our ORR modeling recognize the overall charge-transfer reactions canproceed along both surface pathway via triple-phase boundary (3PB) and a bulk pathway via electrolyte/cathode interface (2PB) of SOFC cathodes. We analyzed the electrochemical behavior of LSM-type MIEC cathode by incorporating multi-step charge-transfer into the bi-pathway kinetics model. The results are compared to the experimental data to examine the physical validity of the assumed oxygen reduction scenario, and the consequent implication on performance improvement methods for SOFC cathode is also discussed. Experimentally, we infiltrated SDC into LSM cathode and showed the significant performance improvement and polarization resistance decrease at 800C.
On the system level, Cr-poisoning from interconnect is still one the major reasons to cause system performance degradation. Mn-Co spinel has been identified as the most promising candidate for SOFC interconnect coating due to its high electrical conductivity, capability to block chromium evaporation, and match with CTE with other cell components, etc. We developed low-cost coating methods by electroplating and electrophoretic deposition (EPD). Electroplating of alloys, followed by controlled oxidation to the desired spinel phase, offers advantages in terms of low cost and applicable to complex shapes, as compared to other coating methods. However, the huge difference on standard deposition potentials between Co2+/Co (-0.28VSCE) and that of Mn2+/Mn(-1.18VSCE)makes it very difficult to co-deposit Mn-Co alloys. We have been successfully co-deposited the alloys by optimizing bath chemistry, deposition voltage and current, as well as the deposition cycles during the pulse plating process.