In general, reversible solid oxide electrolysis cells (SOECs) can be used for the high-temperature H2O/CO2 co-electrolysis process to generate syngas with high efficiency. As the cathode materials, Sr2Fe1.5Mo0.5O6-delta has various choices of B-site cations in a wide range of compositions, offering flexibility in setting their properties. 10% Fe is doped in the B-site of Sr2Fe1.5Mo0.5O6-delta. Furthermore, in situ grown Fe-ceramic composite cathode provides massive and efficient triple-phase boundary (TPB) for the H2O/CO2 co-electrolysis process after reduced. The Fe nanoparticles distributed on Sr2Fe1.5Mo0.5O6-delta substrate are demonstrated by the X-ray diffraction (XRD), the X-ray photoelectron spectroscopy (XPS), the scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The current density reaches 1.27 A cm(-2) at 1.6 V and 850 degrees C on the solid oxide Sr2Fe1.6Mo0.5O6-delta-SDC/LSGM/Sr2Fe1.5Mo0.5O6-delta-SDC cell. The highest current efficiency of similar to 91% is harvested at 1.3 V. The cell shows highly stable long-term performance after 100 h operation. (C) 2019 Elsevier Ltd. All rights reserved.