The purpose of this study was to use a spinel structure to improve the performance and stability of chemical looping combustion processes. The oxygen carrier employed was Fe2MnO4, in which Ni was substituted at the Fe sites. Fe2-xNixMnO4 spinel particles were successfully synthesized by a sol-gel method. The obtained particles were characterized by X-ray diffraction (XRD), scanning electron microscopy, and CH4-/CO-temperature programmed desorption experiments. The XRD analysis confirmed that all the synthesized particles presented spinel structure. The performance of the particles was evaluated in redox cycle experiments under H2/air and CH4/air at 850 °C using a thermogravimetric analyzer. The Ni-substituted particles exhibited a higher performance than Fe2Mn1, being Fe1Ni1Mn1 the sample with the highest oxygen transfer capacity (19.68 wt% in H2/air and 15.90 wt% in CH4/air).