Design of High‐Performance MnCo _1.5 Cu _0.5 O ₄ Spinel Contact Material with Optimized Electrical Conductivity and Thermal Stability for Solid Oxide Electrolysis Cells by Cu Doping

As promising contact material candidates in solid oxide cells, spinel‐type MnCo 2‐x Cu x O 4 (0 ≤ x ≤ 0.5) and Cu 1.5 Mn 1.5 O 4 powders were synthesized via sol–gel and co–precipitation methods to investigate the effects of Cu doping on electrical and structural properties. Cu substitution introduced additional variable‐valent cations and elevated Mn oxidation state via charge compensation. This valence modulation promoted electron hopping between abundant Mn 4+ /Mn 3+ and Cu 2+ /Cu + redox pairs, leading to higher electrical conductivity. Cu doping also reduced lattice rigidity, as evidenced by increased thermal expansion coefficients. After 1000‐h aging at 850 °C in air, a multi‐layer assembly with MnCo 1.5 Cu 0.5 O 4 as contact layer exhibited a stable area‐specific resistance (ASR) value of ~10 mΩ cm 2 and good compatibility with MnCo 2 ‐coated SUS441 interconnects. Post‐mortem analysis revealed that the resistance was mainly attributed to a well‐defined Cr oxide interlayer. Though Cu 1.5 Mn 1.5 O 4 contact layer led to a thinner oxide scale, continuous Cr outward diffusion may deteriorate the cell performance. Finally, MnCo 1.5 Cu 0.5 O 4 was applied to a single‐cell stack under H 2 O/CO 2 co‐electrolysis operation for 600 h and achieved an electrolysis voltage of ~1.3 V at a current density of 0.4 A cm −2 . Overall, Cu‐doped Mn‐Co spinels demonstrate great potential as highly conductive contact materials with tunable thermal properties for solid oxide electrolysis cell applications.