Ceria Coatings Effect on H[sub 2]S Poisoning of Ni/YSZ Anodes for Solid Oxide Fuel Cells

Abstract

Ceria is a good sulfur sorbent under reducing atmospheres because of its high affinity for sulfide at high temperatures. In this study, to enhance the sulfur tolerances of anodes for solid oxide fuel cells, we have used a dip-coating method to modify the pore wall surfaces of conventional nickel/yttria-stabilized zirconia (Ni/YSZ) anodes by coating them with ceria nanoparticles (10–20nm) . We have monitored the sulfur poisoning process in various normalH2S concentrations at 700°C . Because the ceria reacted with normalH2S to form normalCe2normalO2S , which acted as a sulfur sorbent, normalNi3normalS2 was hardly formed in the ceria-coated Ni/YSZ anode; therefore, its performance dropped to a lesser degree relative to that of the conventional Ni/YSZ anode. Furthermore, impedance spectroscopy revealed that the polarization resistance increased upon increasing the normalH2S concentration. Our results suggest that ceria nanocoatings on Ni–YSZ anodes provide greater sulfur tolerance at higher normalH2S concentrations (⩾200ppm) and lower operating temperatures (700°C) .

Oxide incorporation into Ni-based solid oxide fuel cell anodes for enhanced sulfur tolerance during operation on hydrogen or biogas fuels: A comprehensive thermodynamic study

“…This means that, although CeO 2 -modified anodes can exhibit superior performance in comparison to unmodified Ni-YSZ anodes, power output drop due to sulfur poisoning of Ni catalyst is unavoidable. These thermodynamic findings are in perfect agreement with the experimental results of Yun et al [8]. These authors also verified, in a more recent experimental study [9], that the performance of CeO 2 -modified anodes can be increased when SDC (Ce 0.8 Sm 0.2 O 2 ) is used instead of pure ceria.…”

“…The degree of sulfur poisoning is greater for biogas compositions with lower CH 4 /CO 2 molar ratios. 8 r e f e r e n c e s…”

“…From recent experimental results reported in the literature, one can see that Ni-YSZ anode infiltrated by BaO [10] or BaZr 0.1 Ce 0.7 Y 0.2 Yb 0.2Àx Yb x O 3Àd (BZCYYb) [12] exhibits no obvious change in stability and power output for SOFCs operating on H 2 S-containing hydrogen fuel, under humidified conditions. Although CeO 2 -modified anodes are claimed to have enhanced sulfur tolerance over the conventional Ni-YSZ anode, loss in performance due to sulfur poisoning of Ni catalyst is unavoidable [8,9,13]. The aforementioned experimental observations still require a detailed theoretical analysis for improving the understanding of the involved phenomena.…”

Electrochemical Analysis of a System Based on W and Ni Combined with CeO2 as Potential Sulfur‐tolerant SOFC Anode

“…Good fitting between the equivalent circuit and the experimental was observed. This equivalent circuit has been used by other authors to analyze H 2 S poising mechanism [21,26,32] and hydrogen oxidation varying the fuel utilization and gas flow rate in a SOFC cell [27]. In addition, we have also employed this model to study the methane oxidation in cells [25,28].…”

“…) could be related to diffusion processes [21,32] and/or bulk processes that might have been caused from the density changes resulting from the formation of NiS, WS 2 , and Ce 2 O 2 S from Ni, W and CeO 2 , after introducing H 2 S, thereby leading to decreased porosity and pores sizes of the anode. Alternatively, it is also possible that the increase of the LF arc could be related to changes in surface property after introduction of H 2 S, for example, surface exchange reactions not including electron transfer or surface diffusion.…”