Heterogeneous functional materials play very important roles in solid oxide electrochemical cells in intermediate temperatures (400-600^oC). At this temperature regime, the solid oxide electrochemical cells can compromise the disadvantages from lower and higher temperature counterparts by adopting more cost-effective catalysts and materials as the cell components while mitigating the fast degradation to achieve optimal reaction kinetics. More importantly, it allows many nano-sized catalysts to be functioning that can be ultimately integrated into the real device through advanced manufacturing technologies. At Idaho National Laboratory, we developed a series of strategies to accommodate heterogeneous functional materials for a range of applications, including hydrogen production via water electrolysis, CO₂ conversion and ammonia electrosynthesis using protonic ceramic electrochemical cells (PCECs). The special emphasis is placed on the effect of structure, composition, morphology, and defects of these materials on electrochemical performance of PCECs and respective product for a given feedstock.