Characterization of Cobalt-Manganese Spinel Thin Films (CoMn₂O₄ and MnCo₂O₄)

Recent investigations on the spinels CoMn₂O₄ and MnCo₂O₄ have shown their potential for applications in water splitting and fuel cell technologies as they exhibit strong catalytic behavior through oxygen reduction reactivity. To further understand these materials, cobalt-manganese spinels were synthesized as thin films using molecular beam epitaxy and characterized using experimental analyses. The Co_xMn_3-xO₄ samples vary in composition between Co₃O₄ and Mn₃O₄ to establish links between cation stoichiometry and material properties. Experiments that include in-situ x-ray photoelectron spectroscopy, x-ray diffraction, x-ray absorption spectroscopy, and spectroscopic ellipsometry reveal information on properties such as cation valence states, bond lengths and coordination, as well as electronic structure with references to density-functional theory models. The findings provide insights into the entire cobalt-manganese spinel system and related spinel oxides that are promising candidates for inexpensive oxygen reduction reaction catalysts.