By Jensen Karin Vels
The anode/electrolyte interface ш strong oxide gasoline cells (SOFC) is understood to reason electric losses. Geometrically easy Ni yttria-stabilised zirconia (YSZ) interfaces have been tested to realize info at the structural and chemical adjustments taking place in the course of experiments at 1000°C in an environment of ninety seven% H2/3% H20. Electrochemical impedance spectroscopy at open circuit voltage (OCV) and at anodic and cathodic polarisations (100 mV) was once played. A correlation of info with the constitution improvement and the chemical composition was once tried. Nickel wires with diversified impurity content material (99.8% Ni and 99.995% Ni) have been used to check the impression of impurities at the polarisation resistance and phone sector morphology. The electropolished nickel wires have been pressed opposed to a refined eight mol% YSZ surface.Extensive structural adjustments from a flat interface to a lull and valley constitution have been came across to ensue ш the touch sector with the impure nickel cord, and a ridge of impurities was once equipped alongside the rim of the touch region. Impurity debris within the interfacial area have been additionally saw. The impurity part was once defined as an alkali silicate glassy part. No modifications have been discovered among polarised and non-polarised samples. With natural nickel wires, despite the fact that, the microstructures relied on the polarisation /non-polarisation stipulations. At non-polarised stipulations a hill and valley style constitution was once discovered. Anodic polarisation produced an as much as 1 um thick interface layer together with nano-sized YSZ debris with a few Ni current. At cathodic polarisation either a granulated constitution and a lull and valley constitution equivalent to the constitution of non-polarised samples have been came upon. Small impurity ridges have been surrounding the touch parts on non-polarised and cathodically polarised samples. TOF-SIMS and XPS analyses confirmed the presence of impurities in either the impure and natural touch parts. The impedance spectroscopy printed that counting on the impurity content material of the nickel, diversified advancements of the polarisation resistance with time came about. At open circuit voltage the samples with impure nickel electrodes confirmed an preliminary raise towards a excessive consistent polarisation resistance, while the samples with natural nickel electrodes confirmed a substantial reduce to a low consistent polarisation resistance with time. For either sorts of nickel the polarisation resistance dropped upon polarisation. the world particular polarisation resistances for the samples with natural electrodes have been nearly 10 instances under for samples with impure electrodes. This used to be mostly ascribed to the impurity content material and distribution, either within the 3 section boundary region and as a kind of non-stop movie masking the interfacial area. The drop within the Rp upon polarisation can be ascribed to adjustments ш the distribution of the impurity part within the interfacial quarter.
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Extra resources for The Ni-YSZ interface
The sample that was annealed in air show a lower concentration of carbon (16 atom%) than samples, which were not annealed (60 atom%). This is explained by combustion of the organic material in air at elevated temperatures. The sample that was annealed in hydrogen shows a higher carbon content (35 atom%) than the air-annealed sample, but still it was lower than the samples, which were not annealed. In hydrogen the carbon species do not combust but are converted to CH4, which is a slow process. The carbon on the fresh fracture sample (13 atom%) is representative for the airborne species settling immediately on the surface when the sample is exposed to air.
Light areas are high and dark areas are low. The rim ridge is seen as a thin, white line through the image. In the contact area a hill and valley structure has developed. C) The line profile shows that the rim ridge is around 18 nm high in this place (arrows). The width of the rim ridge is 150 nm. 24 Fig. 16. A) AFM image of the hill and valley structure (sample 124n) of one of the grains from fig. 15a. The pyramid-shaped hills are aligned in regular patterns. Along the grain boundaries there is a row of pyramids.
From the shape of the rim ridge it is deduced that the interfacial impurity phase is sufficiently mobile to assume equilibrium shape. The driving force for interface formation is the decrease in free energy, ∆G, when a common interface is established. 1) where the γ’s are interface energies between liquid (L) (or mobile phase), solid (S) and vapour (V) phases . The Ni-YSZ-hydrogen-impurity phase(s) system is much more complicated than that, but the same principles apply. The contact angle, θ, between the solid and liquid, specifies the condition for minimum surface energy: γ LV cosθ = γ SV − γ SL .
The Ni-YSZ interface by Jensen Karin Vels