Toward Cobalt-Free SOC Stacks: Comparative Study of (Mn,Cu,Fe)3O4 vs. (Mn,Co)2O4 Spinels as Protective Coatings for SOFC Interconnects

The paper presents the experimental results of applying a novel protective coating made from Mn1.7Cu1.3-xFexO4, compared to commercial spinels Mn1.5Co1.5O4 and MnCo2O4, as a key component responsible for preventing chromium diffusion and slowing the increase in area-specific resistance (ASR) in solid oxide fuel cells (SOFCs). The layers of selected materials were deposited on Crofer 22APU steel by electrophoretic deposition (EPD) on small samples and by roll painting on full-scale interconnects. The coatings were evaluated by measuring the ASR of small samples for short and long runs (1000 h), as well as real-scale interconnects assembled in a SOFC stack composed of three cells, measuring 11 × 11 cm2, which operated for 1000 h at 670 °C. The collected data on the electrochemical performance of the stack allowed for estimation of the degradation rates of all the repeating units, revealing benefits from using (Mn,Cu,Fe)3O4 as a coating. The results are compared to the literature reports. Post-mortem analysis by the SEM-EDS technique allowed for investigation of Cr diffusion levels.