In situ probing of the mechanisms of coking resistance on catalyst-modified anodes for solid oxide fuel cells

Abstract

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, BaZr0.9Y0.1O3-d (BZY), and BaZr0.1Ce0.7Y0.1Yb0.1O3-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 -CO3 groups reveal the interactions between surface functional groups and gas species (hydrocarbon, water steam, and CO2). While the switching from -OH to -CO3 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 -CO3 is found effective for carbon removal only on the BZCYYb surface.