In situ Raman and optical characterization of H2S reaction with Ni-based anodes for SOFCs

• We re-assessed the use of in situ Raman spectroscopy to check the sulfidation of SOFC anodes which works well up to 500 °C.
• At high temperatures, nickel sulfide crystals’ growths is seen via optical microscopy, while no Raman bands can be obtained.
• At low temperature, Raman spectra indicate a severe poisoning caused by a H2S contact at 500 °C and during slow heating.
• The crystals’ growths observed in situ suggest the diffusion of nickel toward sulfide species.
• The reaction between H2S and CGO was detected at 750-790 °C, that between H2S and Ni is favorable at lower temperatures.

In this paper, we re-assess the use of Raman spectroscopy as an in situ method to monitor the sulfidation of SOFC (solid oxide fuel cell) anode-based materials. The technique allows studying in situ kinetics of the sulfidation of nickel at low temperature (up to 500 °C). A severe poisoning happens at 500 °C with a layer of Ni3S2 covering the entire pellet surface. At higher temperatures, optical microscopy helps to observe in situ the formation and growth of nickel sulfide crystals for the first time. The crystals' growths observed in situ strongly suggest the diffusion of nickel toward sulfide species. A reaction between H2S and CGO was clearly observed at 750–790 °C.