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a b s t r a c tNi-YSZ cermet is commonly used as the anode of a solid oxide fuel cell (SOFC) because it has excellent electrochemical performance, not only in hydrogen fuel, but also in a clean blended synthetic coal syngas mixture (30% H 2 , 26% H 2 O, 23% CO, and 21% CO 2 ). However, trace impurities, such as phosphine (PH 3 ), in coalderived syngas can cause degradation in cell performance [J.P. Trembly, R.S. Gemmen, D.J. Bayless, J. Power Sources 163 (2007) 986-996]. A commercial solid oxide fuel cell was exposed to a syngas with 10 ppm PH 3 under a constant current load at 800 • C and its performance was evaluated periodically using electrochemical methods. The central part of the anode was exposed directly to the syngas without an intervening current collector. Post-mortem analyses of the SOFC anode were performed using Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results show that the impurity PH 3 caused a significant loss of the Ni-YSZ anode electrochemical performance and an irreversible Ni-YSZ structural modification. Ni 5 P 2 was confirmed to be produced on the cell surface as the dominant nickel phosphorus phase.

Coking is a major cause of performance degradation of Ni-based anodes in solid oxide fuel cells (SOFCs) powered by carbon-containing fuels. While modification of Ni surfaces using a thin coating of BaO, BaZr 0.9 Y 0.1 O 3−d (BZY), and BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−d (BZCYYb) was reported to alleviate the problem, the mechanism is yet to be understood. In this study, in situ Raman spectroscopy and surface enhanced Raman spectroscopy (SERS) are used to probe the surface chemistry of BaO, BZY, and BZCYYb. Analyses of the time-resolved spectral features of C−C bonds, −OH groups, and −CO 3 groups reveal the interactions between surface functional groups and gas species (hydrocarbon, water steam, and CO 2 ). While the switching from −OH to −CO 3 groups is irreversible on BaO surfaces, it becomes reversible on both BZY and BZCYYb surfaces. Although the −OH mediated carbon removal is observed on the surfaces of all three catalysts, the −CO 3 is found effective for carbon removal only on the BZCYYb surface.

In this research, the polarization behavior and kinetic pathways of an SOFC cathode have been investigated with a 1-D continuum model incorporating material physical properties and surface potential effects into a multi-step ORR kinetic formalism. It is found that (1) Two different types of 3PB-to-2PB pathway transitions can be identified. A strong 2PB pathway contribution leads to an explicit transition, while an implicit transition implies more favorable 3PB kinetics. The predicted kinetic trends qualitatively agree with literature results on single-phase LSM cathodes in different configurations and operation conditions; (2) The explanation for the different transition modes concerns the fact that the mass transport limitation of the 3PB path is more easily reached (at lower overpotential) when incorporation kinetics are favored by the material properties; and (3) The surface potential is found to strongly control the oxygen adsorption by introducing a rate-limit for cathodes with lower oxygen coverage, and can drive the incorporation faster under 3PB-favorable states.