Entropy-engineered Ni–Mn–Co spinel coatings via microwave sintering for ultra-stable SOFC interconnects

Microwave-sintered Ni-doped Mn–Co spinel coatings were developed as advanced protective layers for solid oxide fuel cell (SOFC) interconnects. By systematically varying the Ni content (in MnCo_2-xNi_xO₄, x = 0–0.5), we demonstrate that Ni incorporation significantly alters cation valence distributions and oxygen vacancy concentrations, leading to a substantial reduction in the thickness of Cr-containing oxide layers compared to undoped coatings. Among the compositions studied, the MnCo_1.7Ni_0.3O₄ coating exhibited the best performance, maintaining an area-specific resistance (ASR) below 20 mΩ cm² after 500 h at 800 °C, indicating excellent electrical conductivity and long-term stability. Crystal field analysis revealed that Ni doping not only suppresses the Jahn-Teller distortion of Mn³⁺ but also enhances configurational entropy, thereby stabilizing the spinel structure against Cr diffusion. These findings establish entropy engineering via Ni substitution as a viable strategy for designing thermodynamically robust, electrically conductive, and Cr-resistant coatings, offering a promising pathway for durable SOFC interconnect applications.