A composite electrolyte, Zr doped BaCe0.8Y0.2O3-delta (BaCe0.8Y0.2O3-delta, BCZY) and binary carbonates [(Li,Na)(2)CO3] (LNCO) was first applied to reduce CO2 accompanied with steam electrolysis in solid oxide electrolysis cell (SOEC) at 600 degrees C, lower than which conventional SOEC composed by YSZ works in (usually above 800 degrees C). Electrolysis performances are improved due to sufficient steam feed at oxygen electrode side (30-110 ml/min). Steam electrolysis provides proton source for the reduction of CO2. Application of composite electrolyte promotes proton transport and directly leads to H-2 even CH4 production. To a certain degree, carbon resistance guarantees the symmetric SOEC operation at a lower bias potential of 0.5 V (vs.00V) applied. A redox-stable and carbon-tolerant LSCM as symmetric electrode with a hybrid-ion-conducting composite electrolyte realizes the fuel synthesis by CO2 reduction in proton-type solid oxide electrolyzer. (C) 2016 Elsevier Ltd. All rights reserved.