Long-term stability and oxidation behavior of Mn2CuO4, Mn1.9Fe0.1CuO4, Mn1.7Fe0.3CuO4 coatings on SOFC interconnects: summary of a 10,000-h oxidation test

Abstract

This study presents the long-term stability and protective performance of spinel (Mn,Cu,Fe)₃O₄ coatings deposited on ferritic stainless steel Crofer 22 APU. The spinel coating was submitted to a 10,000-h oxidation test at 750 °C. Three spinel oxides with varying iron content (x = 0; 0.1; 0.3) were synthesized via the sol-gel method and deposited by electrophoretic deposition (EPD). During the characterization an oxidation kinetics, coating microstructure, electrical properties, and chromium retention capability were monitored. The results show that the addition of iron significantly improves the phase stability, reduces oxidation rate constants, and limits the growth of chromium oxide layers. Among tested spinel oxides the Mn_1.7CuFe_0.3O₄ coating exhibited the best performance, maintaining a low area-specific resistance (ASR ∼3.8 mΩ cm²) after 10,000 h and effectively suppressing chromium diffusion. Structural analyses using SEM, TEM, EDS, and Raman spectroscopy confirmed the formation of a dense and adherent protective layer with limited porosity and chromium content. Fuel cell aging tests confirmed the coating's protective capabilities, demonstrating minimal performance degradation and reduced Cr deposition on the cathode surface. Obtained results put more light on Mn-Cu-Fe spinels properties revealing their attractivity as an interesting cobalt-free, economically attractive and durable alternative for next generation SOCs interconnect protection.