Due to the susceptible reaction BaCeO₃-based proton-conductors toward steam and carbon dioxide, La₂Ce₂O₇(LCO) is proposed as a protect layer on top of solid electrolyte since LCO has shown high proton conductivity with adequate stability against steam. In the study, La(NO₃)₃·6H₂O and Ce(NO₃)₃·6H₂O were used as precursors to obtain La₂Ce₂O₇(LCO). Particle size analyzer and XRD are applied to analysis this result. From the XRD analysis, it can be seen at the temperature range above 900°C, the reflections representing fluorite-structured LCO appeared with other reflections from BaCe_0.5Zr_0.3Y_0.2O_3-δ(BCZY) perovskite substrate. The result can also demonstrate that there is no reaction between LCO layer and BCZY substrate. It is suggested that LCO exhibits good chemical compatibility with BCZY. This synergic bilayer electrolyte design may be a feasible design to overcome the instability of Zr- or Ce-rich Ba(CeZr)O_3−δ electrolysis cells against steam and CO₂ for better long-term performance. The stability and protection of La₂Ce₂O₇(LCO) on BaCe_0.5Zr_0.3Y_0.2O_3-δ(BCZY) will be evaluated based on structural and electrical properties measurement under humid and CO₂ containing environment as function of time and temperatures.