Recent advances on spinel-based protective coatings for solid oxide cell metallic interconnects produced by electrophoretic deposition

Manganese–Cobalt Based Spinel Coatings Processed by Electrophoretic Deposition Method: The Influence of Sintering on Degradation Issues of Solid Oxide Cell Oxygen Electrodes at 750 °C

“…More interesting features can be appreciated by comparing the SEM images previously described, of 20s_Ox and 20s_Red, with those of the coating after the re-oxidation step (20s_RedOx), thus at the end of the two-step sintering process; the SEM cross sections and top-view images are presented in Figure 3 a–d. During the re-oxidation step, MnO and Co are reported to react, in order to re-form the spinel structure and bringing benefits in terms of densification [ 20 , 25 , 29 , 32 ]. To this purpose, the most evident characteristic is the significant densification (80%) that is reached after the re-oxidation step, with a final coating thickness of around 12 µm ( Figure 3 a,b).…”

“…The influence of the spinel coating microstructure (i.e., densification derived by different sintering treatments) on the Cr and Mn possible migration from the steel has already been discussed in various references. To this purpose, the importance of achieving a highly densified coating layer at the steel interface, to limit Cr and Mn diffusion, is reviewed in [ 20 ]. Moreover, a possible diffusion mechanism has already been proposed by Talic et al [ 30 ], where the poorly densified oxidized spinel coating is shown to undergo slower, but continuous, densification at the steel interface during long-term aging.…”

“…For example, sputtering [ 11 , 12 ], electroplating [ 13 ], and plasma spray [ 14 ] allow highly dense coatings to be obtained, and a sintering treatment may not be required. On the other hand, when screen printing [ 15 , 16 ] or slurry-based methods, such as deep coating [ 17 , 18 ] and electrophoretic deposition (EPD) [ 19 , 20 , 21 ], are used, a post-deposition treatment is always required, in order to consolidate and densify the deposited powders and reduce the residual porosity. EPD is a fast and versatile process that allows homogeneous layers to be deposited in few seconds, and in a RT condition on complexly shaped steel components [ 22 , 23 , 24 ].…”

“…However, a certain degree of porosity can be considered beneficial, as this might stop possible cracks from propagating further. Although a two-step sintering process, consisting of a reduction followed by a re-oxidation step, is widely recognized as a valid post-deposition treatment to achieve high coating densification, it causes an increase in the processing cost of the interconnect [ 20 , 29 ]. Indeed, even poorly densified spinel coatings subjected to the one-step sintering in air could only ensure sufficient protection against Cr vaporization and corrosion of the interconnect during the stack operation at 800 °C [ 30 ].…”

TEM Characterization of Long Term Aged Interconnect Oxide Layers from Real Stack

“…Several deposition techniques were developed and show promising results for MCO coating on ferritic stainless steel: thermal growth 13 , pulse plating 10 , electroplating 1 , brush painting and infiltration 6 , electrolytic co-deposition of Co and MnO 5 , electrophoretic deposition 9,14,17,18,20,21,23,28 , spray pyrolysis 22,29 , plasma spraying 30 , RF magnetron sputtering 7 , and thermal co-evaporation 7 . Each technique has its advantages, with electrophoretic deposition seemingly the most promising 28 , but their presentation and discussion are beyond the scope of this paper. The numerous studies demonstrate the interest of the community for the coating and its use in the industry.…”