In this study, NiO-Ce0.8Sm0.2O1.9 (NiO-SDC) composite was synthesized through co-precipitation method by changing the NiO volume concentration from 45 to 65%. Then, experimentation was done to add La from 10 to 20 mol% in NiO-SDC composite. Finally, NiO-SDC composite was synthesized by the addition of 5–15 mol% hydrogen peroxide (H2O2) during co-precipitation to improve its properties by process modification. Thermogravimetric analysis showed that the weight loss was approximately same for NiO-SDC and LaNiO-SDC composites. However, the weight loss was greater for NiO-SDC composite synthesized by H2O2 addition during synthesis. X-ray diffraction analysis showed that all the calcined composites exhibited cubic fluorite crystal structure and the addition of La and H2O2 did not alter the phase and crystal structure of NiO-SDC composite. However, with 20 mol% La, there appeared the onset formation of La2NiO4 and LaNiO3 phases. Scanning electron microscopy images showed that the addition of La and H2O2 improves the microstructure of NiO-SDC composite through the formation of homogeneously dispersed particles.