Long Term Resistivity Behavior of SOFC Interconnect/Ni-Mesh/Anode Interfaces

Abstract

Contact resistances between Crofer 22 APU and Crofer 22 H interconnect plates, Ni mesh and Ni-8YSZ anode interfaces were measured under an anode gas atmosphere (97%H 2 + 3%H 2 O) at 700 °C and 800 °C and current densities of 0 and 0.7 A/cm 2 for durations up to 3000 hours using the 4-point DC conductivity technique. Phase transformations within the steel samples close to the interface due to inter-diffusion of elements (Ni, Fe, Mn and Cr) were observed and analyzed. These phase transformations and the formation of oxide scales on steel as well as nickel mesh surface and grain boundaries do not seem to substantially affect the measured contact resistance with time.

Post‐test Characterization of Metallic Materials and Adjacent Components in an SOFC Stack After 34,000 h Operation at 700 °C

“…The width of the austenized zone is typically in the range 50 to 100 µm. This is slightly smaller than values which might be expected on the basis of laboratory data up to 3,000 h, described in reference , , assuming a parabolic time dependence of the nickel penetration depth into the steel. The reason for this difference might be, that the data in from laboratory tests were estimated using Ni/steel contacts obtained using spot welding.…”

Long-term behaviour of solid oxide fuel cell interconnect materials in contact with Ni-mesh during exposure in simulated anode gas at 700 and 800 °C

“…The reason for Laves-phase dissolution is thought to be the enrichment of Nb in the outer part of the Ni layer and a depletion of Nb in the subsurface zone of the steel. In spite of the fact that no contact resistance measurements were carried out, it seems that the microstructure changes at and near the steel-nickel interface do not substantially affect the electrical properties of the joint [18]. Long-term measurements with similar steel-nickel joints at 700 and 800 C in AreH 2 eH 2 O revealed changes of the area specific contact resistance in the range of 1e3.5 mU cm 2 during exposure times up to 3000 h. This result indicates that possible adverse effects of the nickelesteel interaction on the electrical properties seem to be less important than changes of the mechanical and/or physical properties of the interconnect and/or nickel wire mesh.…”

“…Formation of s-phase near the contact area between a Nimesh and the ferritic steel Crofer 22H has been observed after exposure in Are4%H 2 e2%H 2 O at 800 C for 1000 h [18]. Niewolak et al [12] found that s-FeCr precipitates formed in the interdiffusion zone, i.e.…”

Enhancing the Robustness of Brittle Solid Oxide Cell Stack Components

“…Other critical interfaces in planar SOC stacks are those between the cell and the interconnect. On the fuel electrode side Ni meshes or foams can be used to ensure good adhesion and current distribution (7)(8)(9). However, the adherence between the oxygen electrode and the interconnect is more challenging.…”