Degradation Of Solid Oxide Fuel Cells Research Articles

Chemical durability of Solid Oxide Fuel Cells: Influence of impurities on long-term performance

Because of the fuel flexibility of Solid Oxide Fuel Cells (SOFCs), various types of fuels may be applied directly or via a simple reforming process, including hydrocarbons, alcohols, coal gas, biogas, besides hydrogen. However, various types of minor constituents in practical fuels and/or from the system components can cause chemical degradation of SOFCs, such as anode and cathode poisoning phenomena. In this study, we compare the influence of various external impurities, including sulfur, chlorine, phosphorus, boron, and siloxane for anodes, and H 2O and SO 2 for cathodes, on SOFC performance to have a general overview on long-term chemical durability of SOFCs. Chemical compatibility of Ni with foreign species has also been thermochemically considered. Using common model cells, the stability of cell voltage, electrode overpotential, and ohmic loss up to 3000 h has been experimentally examined for H 2-based fuels, for hydrocarbon-based fuels, and for partially pre-reformed CH 4-based fuels. Increase in degradation rate by impurities was verified for various operational parameters. Impurity poisoning mechanisms are discussed for each specific impurity.

A prefilter for mitigating PH 3 contamination of a Ni-YSZ anode

Ni-YSZ is used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance for operation with coal-derived syngas. However, trace impurities, PH 3 H 2S AsH 3, and Sb in coal-syngas can cause SOFC degradation. Described here is a means of removing PH 3 impurity from syngas by using a Ni-based prefilter. In one test, a thin Ni-based filter was set upstream of a Ni-YSZ anode-supported SOFC. The SOFC was exposed to syngas with PH 3 under a constant current load at 800 °C. The filter decreased 20 ppm PH 3 in the feed to a level which did not degrade the SOFC for over 400 h until the filter became saturated. In another test, both H 2S and PH 3 were co-fed to the cell with Ni-based and Fe/Ni-based filters. The interaction between these two impurities did not significantly impact the filter performance with respect to PH 3 removal for both filter formulations. The cell performance was evaluated by current–voltage measurements and impedance spectroscopy. Post-mortem analyses of the cell and filter were performed by means of XRD, SEM/EDS and XPS. With proper filter design, the Ni-YSZ SOFC can operate on contaminated coal-syngas without degradation over a prescribed period of time.

Fast performance degradation of SOFC caused by cathode delamination in long-term testing

The performance degradation of a solid oxide fuel cell (SOFC) single cell caused by delamination of the cathode is investigated. When the TEC difference between the cathode and the electrolyte is large, detachment of the interface occurs. This is confirmed by SEM images and impedance analysis during long-term operation. As delamination occurs, the active area naturally decreases, and the oxygen reduction reaction concentrates into the intact area. This leads to an increase in polarization and ohmic losses so that the performance of the single cell degrades by approximately 7.7% during 1000 h of operation. Assuming that the drop of power density was due only to delamination, the area change is approximately 10% when the TEC difference is 7 × 10 −6 K −1.

Degradation in Solid Oxide Fuel Cells Operating with Alternative Fuels

Solid Oxide Fuel Cells (SOFCs) have been shown to generate power with a wide variety of hydrocarbon based fuels. The operation of SOFCs with alternative fuels is hindered by carbon deposition and sulfur poisoning. Here we analyze the performance and degradation of SOFCs with different types of anode, including Ni-YSZ, Cu-ceria, and Rh-ceria based anodes. The tested fuels include Pennsylvania crude oil, JP-7 and JP-8 Plus jet fuels, waste vegetable oil, ethanol, and biodiesel. The performance of the cell with each fuel was characterized with cell voltage vs. current density curves, degradation tests, and electrochemical impedance spectroscopy measurements.

Fused LSM: A Novel Powder Limiting the Formation of La2Zr2O7 and SrZrO3 Resistive Phases at the Interface with YSZ in SOFC Cathodes

In solid oxide fuel cell (SOFC) on the cathode side, the formation of highly electrically resistive phases as La2Zr2O7 (LZO) or SrZrO3 (SZO) at the triple-phase boundary between LSM, YSZ and air decreases the performance of the cell and is partially responsible for the long term degradation of the SOFC. Saint-Gobain Company is making LSM material by fusion process. The reactivity of LSM made by fusion and conventional methods with 8YSZ was compared. Ageing tests were performed by increasing the temperature over 1100{degree sign}C and in several atmospheres (air and N2). Whatever the conditions are, the reactivity of fused LSM is barely if not observable whatever the Sr content is, whereas LSM powders made by conventional methods lead to the formation of LZO or SZO as a function of Sr content. Thus, LSM made by fusion process is a promising material for cathodes to avoid the long term degradation of SOFC.

Ni/YSZ Anode Interactions with Impurities in Coal Gas

Performance of solid oxide fuel cell (SOFC) with nickel/zirconia anodes on synthetic coal gas in the presence of low levels of phosphorus, arsenic, selenium, sulfur, hydrogen chloride, and antimony impurities were evaluated. The presence of phosphorus and arsenic led to the slow and irreversible SOFC degradation due to the formation of secondary phases with nickel, particularly close to the gas inlet. Phosphorus and antimony surface adsorption layers were identified as well. Hydrogen chloride and sulfur interactions with the nickel were limited to the surface adsorption only, whereas selenium exposure also led to the formation of nickel selenide for highly polarized cells.

Effect of Coal Gas Contaminants on Solid Oxide Fuel Cell Operation

The operation of solid oxide fuel cells (SOFC) was evaluated on simulated coal gas in the presence of several coal gas impurities that are expected to remain in low concentration after warm gas cleanup. Phosphorus, arsenic and sulfur were considered in this study. The presence of phosphorus and arsenic in low, 1-2 ppm, concentrations led to the slow and irreversible SOFC degradation due to the formation of the secondary phases with nickel in the upper part of the nickel-based anode close to the gas inlet. Sulfur interactions with the nickel were limited to the surface only. Cell performance losses due to sulfur exposure were reversible and independent of the presence of other impurities.