Crack severity in relation to non-homogeneous Ni oxidation in anode-supported solid oxide fuel cells

Ni-8YSZ cermet re-oxidation of anode supported solid oxide fuel cell: From kinetics measurements to mechanical damage prediction

“…These results are in good agreement with the reported literature [6,18,27] considering two types of oxidation mechanisms depending on the temperature: the first one corresponds to a homogenous oxidation on the overall composite at low temperature; whereas the other one leads to an oxidation gradient. However, different values are reported in literature for the threshold T separating these two mechanisms.…”

“…Indeed, as shown in the previous section, the heterogeneous process at T ¼ 800 C induces a cell curvature with a compressive component in the electrolyte: this compression acts as a 'shielding stress' which shifts the fracture to higher DoO. It can be mention that the calculated DoO Ã 800 C is consistent with the value found by Young et al [27]. Indeed, they have experimentally shown that the first cracks develop on the surface of the electrolyte at T ¼ 800 C as soon as the re-oxidation reaches DoO z 61%.…”

“…However, different values are reported in literature for the threshold T separating these two mechanisms. Ettler et al [6] state that oxidation is homogeneously distributed for T < 700 C; whereas, it is suggested in the present study, in agreement with Young [27], that oxidation is homogenous up T ¼ 750 C. This slight discrepancy could be explained by the difference in microstructures that could arise in the different cermets considered for these studies. Since the definition of a unique critical threshold T between the oxidation processes is difficult, it is more likely that the transition spreads over the T range 700e750 C.…”

“…A special attention has been paid to take into account the heterogeneity of the oxidation across the substrate. Indeed, it has been shown that the cermet oxidation is homogeneous on the whole substrate at 600 C [6,18,27], whereas a Ni/NiO gradient arises in the thickness of the porous substrate for T > 700 C according to Young et al [27] and T ! 700 C according to Ettler et al [6].…”

“…700 C according to Ettler et al [6]. It has been suggested that the heterogeneous oxidation at high temperature could be linked to a O 2 concentration gradient due to gas diffusion in the depth of cermet [27].…”