Characterization of sulfur poisoning of Ni–YSZ anodes for solid oxide fuel cells using in situ Raman microspectroscopy

Redox dynamics of sulphur with Ni/GDC anode during SOFC operation at mid- and low-range temperatures: An operando S K-edge XANES study

“…But, up to now, spectroscopic measurements with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or, Raman microspectroscopy either obtain information from SOFC anode surface in the presence of H 2 S, H 2 , and, possibly even heat, or ex-situ and under postmortem conditions [14,15,22,33]. The molecular structure of sulphur compounds has been studied with sulphur K-shell edge Xray absorption spectroscopy in various fields of application, particularly in relation to fossil fuels, such as sulphur in coal [34], sulphur in residual oil fly ash [35] and heterogeneous catalysis [36].…”

“…There is some consensus about the first step of poisoning, but there are several significantly different if not controversial views about the second, slower step. Some authors are supporting the idea that slow degradation is caused by the formation of volatile Ni x S y phase, which causes restructuring and degradation of electrode structure [14,15,27]. Sasaki et al proposed that blocking of hydrogen diffusion to the TPB caused by sulphur adsorption leads to the oxidation of Ni at TPB interface, causing depletion of active sites [9].…”

“…Sasaki et al proposed that blocking of hydrogen diffusion to the TPB caused by sulphur adsorption leads to the oxidation of Ni at TPB interface, causing depletion of active sites [9]. Slow decline in performance might also be caused by adsorption of sulphur on nickel surface grains which are more difficult to access, such as pores with bottlenecks [14], or, because of surface reconstruction or recrystallization of nickel grains from catalytically more active into catalytically less active crystallographic form [14], or, because of bulk phase diffusion of sulphur penetrating into Ni grains [14]. One possible reason of slow degradation could be the formation of Ce 2 O 2 S as well as Ce(SO 4 ) 2 at relatively low H 2 S concentrations in reaction with nonstoichiometric CeO n (n < 2), because reduced or doped ceria exhibits significantly larger affinity for H 2 S compared to CeO 2 used in theoretical calculations [20,32].…”

Direct Carbon Fuel Cell System Utilizing Solid Carbonaceous Fuels

“…If carbon is deposited under OCV conditions, it is expected that during cell operation it will be oxidized. Indeed, a recent study employing in situ Raman spectroscopy for CO oxidation on Ni/YSZ cermet SOFC anodes at 715 o C reported direct evidence of graphitic carbon formation under open circuit conditions [29][30][31]. However, under current carrying conditions, they reported that the Raman spectra clearly showed the gradual disappearance of the graphitic carbon peak within several minutes, and increasingly faster at larger cell overvoltages.…”

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

“…The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion 2 . Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation [8][9][10][11][12] . It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell.…”