Dense ceramic membranes with mixed protonic-electronic conductivity have been widely studied because of their 100% H-2 selectivity and directly integrated advantage with high-temperature chemical reactions. In this study, Sr-based dual-phase ceramic membrane SrCe(0.95)Fe(0.05)O3(-delta)-SrFe0.95Ce0.05O3-delta (SCF-SFC) with mixed protonic-electronic conductivity was obtained by automatic phase-separation of SrCe0.5Fe0.5O3-delta (SCF55) precursor. After calcination at 1350 degrees C, the rationally designed SCF55 precursor auto-decomposed into two thermodynamically stable oxides: Ce-rich phase SrCe0.95Fe0.05O3-delta and Fe-rich phase SrFe0.95Ce0.05O3-delta that functioned as protonic and electronic conductors, respectively. The compositions and microstructures of the auto-formed phases were studied via XRD and SEM analyses. The dual-phase SCF-SFC membrane shows a high hydrogen permeation flux of 0.38 mL min(-1) cm(-2) at 940 degrees C. Stability tests indicated that the SCF-SFC membrane exhibited higher and more stable hydrogen permeation flux with less degradation under CO2-containing atmospheres compared with the BaCe0.15Fe0.85O3-delta-BaCe0.85Fe0.25O3-delta (BCF-BFC) membrane. This significant improvement can be attributed to the lower CO2 adsorption and reduced carbonate formation which is indicated by thermogravimetric analysis. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.