Reduction of chromium vaporization from SOFC interconnectors by highly effective coatings

The Effect of Metallic Co-Coating Thickness on Ferritic Stainless Steels Intended for Use as Interconnect Material in Intermediate Temperature Solid Oxide Fuel Cells

“…At such high temperatures, two mechanisms that are associated with the interconnect material contribute to the rapid degradation of the fuel cell: increased electrical resistance caused by a growing oxide scale [5] and poisoning of the cathode caused by volatilization of the chromium(VI) species from the Cr-rich oxide scale at the interconnect surface [6][7][8][9][10]. Custom-made steels have been developed to improve oxidation resistance; however, to mitigate Cr vapourization, these steels are coated with an oxide layer that reduces Cr vapourization [9,[11][12][13]. Furthermore, in addition to mitigating Cr vapourization, the coating material should possess high electrical conductivity at the desired operating temperature in order to avoid high electrical resistances caused by the coating.…”

“…These coatings can be applied with a variety of coating methods, such as in powder form [14][15][16][17], by plasma spraying [18,19], or by physical vapour deposition (PVD) [20], to mention a few. An alternative coating process is to coat the steel with a metallic Co layer that is rapidly converted to Co 3 O 4 when heated in air [12,[21][22][23][24]. At 750°C or higher, Mn from the steel will diffuse out into the Co 3 O 4 and form (Co,Mn) 3 O 4 [21-23, 25, 26].…”

“…Earlier generations of SOFCs operated at 800°C or higher, but due to the limited lifetime and the expensive materials necessary for long-term operation at such high temperatures, SOFC developers have put a lot of effort into reducing the operating temperature, and today, several SOFC systems operate in the temperature regime 600-700°C. At 800°C or above, the Cr 2 O 3 scale grows rapidly to become several lm thick [12,13,22,[29][30][31]. Therefore, the electrical resistance of the well-conducting (Co,Mn) 3 O 4 coating is not expected to contribute any significant amount to the total resistance of the oxide scale.…”

Cr-tolerance of the IT-SOFC La(Ni,Fe)03 material

“…1.4) decreasing, and preferably preventing, Crvaporization [19][20][21]. However, taking into account required life-time of 40,000 hours and the possibility of spalling and formation of cracks within interconnect coating layers [19,20] it seems that this approach should not be regarded as a sufficient solution to the Cr-poisoning issue.…”

“…The nearly linear relationship (RThe non-linear time dependent behavior of the electronic conductivity together with the corresponding amount of deposited Cr indicates that the Cr-incorporation in the LNF-layer is not linear in time. One of the possible explanations of the nonlinear Cr-incorporation behavior might be a change in the evaporation behavior of the porous ITM-14 foam-like structure with time, in contrast to a steady Cr evaporation rate reported for the ITM-14 sheet [19,21,49]. To explain this possible change in the Cr evaporation behavior, post-test analysis was performed on the exposed ITM-14 porous foams [56].…”