Evaluation of Cu- and Mn-doped Co3O4/NiO composites as cathodes for intermediate temperature solid oxide fuel cells.

This work advances Co3O4–NiO-based composite cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, we investigate the potential benefits of combining two electronically conducting phases in a composite system (Co3O4/NiO) and of doping this with Mn and Cu. The undoped, Mn-doped, and Mn/Cu-doped composites were synthesised and subjected to comprehensive structural, morphological, and electrochemical characterisation. X-ray diffraction confirmed phase purity, with Mn preferentially incorporating into the Co3O4 lattice, reducing crystallite size and enhancing surface area. Electron microscopy revealed that Mn doping suppressed particle agglomeration, promoting uniform porosity, while dynamic light scattering confirmed the presence of nanoparticles in this composition. Electrochemical impedance spectroscopy demonstrated superior catalytic performance for the Mn-doped composite, with distribution of relaxation time (DRT) analysis indicating accelerated oxygen reduction kinetics. Humidification of the cathode gas slightly increased polarization resistance, which is consistent with electronic conduction being dominant. Thermal stability tests confirmed chemical compatibility with GDC and YSZ electrolytes during annealing at 800 °C for 100 h. The Mn-doped composite emerged as the best candidate, balancing microstructural properties, rapid charge-transfer dynamics, and thermal stability, positioning it as a competitive cathode material for energy-efficient SOFCs.