Monitoring Ag−Cr Interactions in SOFC Cathodes Using Raman Spectroscopy

Abstract

Due to its excellent conductivity and catalytic activity toward oxygen reduction, silver has been used as cathode (or electrocatalyst), current collector, or electrical contact in low-temperature solid oxide fuel cells (SOFCs). Here we report our findings on the contamination of silver or a silver-containing cathode from the chromium oxide layer found on a Cr-containing interconnect. Silver wire was attached to a patterned La 0.8 Sr 0.2 MnO 3 cathode deposited onto a yttrium oxide-stabilized zirconium oxide substrate. The samples were placed inside a temperature-and atmosphere-controlled sample chamber filled with Cr-containing vapor. Raman spectra collected in situ from the sample surface revealed the formation of silver chromate, Ag 2 CrO 4 , on the silver surface at temperatures as low as 500°C. At 625°C, the Ag 2 CrO 4 was found to have vaporized and deposited across the LSM surface. In light of this contamination, special attention should be given to the selection of a metallic interconnect layer for an SOFC system that uses silver or a silver-containing cathode. Further, the use of in situ Raman spectroscopy as a powerful tool for probing and mapping new phase formation on electrode surfaces under fuel cell operating conditions is demonstrated.

Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells

“…[28][29][30] Although there are reports of operando PEM fuel cell water management/transport studies, [31][32][33][34][35][36] no potential-dependent data was provided. This H 2 /air fuel cell spectroscopy uses density functional theory (DFT) calculated normal mode analysis of the Nafion side chain and perfluorinated small molecules to correlate variation of MEA Preparation.-Nafion 117 (Wilmington, DE) was pretreated by immersing sheets in boiling 8 M nitric acid followed by two hours in boiling Nanopure TM water.…”

Novel Composite Materials for SOFC Cathode-Interconnect Contact

“…Both AgCrO 2 and Ag 2 CrO 4 could be formed as a result of the interaction between Ag and Cr in oxidizing environments at elevated temperatures [24][25][26]. EDS analysis of our tested cells revealed the presence of both of these compounds at room temperature.…”

“…The dominant phase, which was observed both in the contact layer and the porous cathode, was Ag 2 (Cr,Mn)O 4 , while only very small amounts of Ag(Cr,Mn)O 2 were detected in the contact layer. The compound Ag 2 CrO 4 is known to have a decomposition temperature of 665°C [25,26], which is well below the melting temperature of pure Ag (962 o C) [27], and also well below the test temperature of our cells (800°C). After reaching its decomposition temperature, Ag 2 CrO 4 is expected to convert to AgCrO 2 and Ag, following the reaction below [25].…”

Need for In Operando Characterization of Electrochemical Interface Features

“…From an overall point of view it appears that the majority of the in situ Raman spectroscopy on solid oxide electrodes has focused on the Ni-YSZ electrode, while perovskite based electrodes so far have been only scarcely investigated (76,77). One may wonder why that is.…”