A composite of (La,Sr)(Cr,Mn)O ₃/(Gd,Ce)O ₂ (LSCM/GDC) was evaluated as a cathode in a high temperature solid oxide electrolysis cell (SOEC) used for steam electrolysis and/or steam-carbon dioxide co-electrolysis. When the steam feed rate was smaller than 30 ml/min, the LSCM/GDC cathode is subject to large diffusion resistance from inadequate steam supply at steam concentration of 3-20%. Sigmoidal shaped I-V curves were thus observed for steam electrolysis, unlike when CO ₂ was present during reduction where smooth I-V characteristics were observed. With respect to steam-carbon dioxide co-electrolysis, the LSCM/GDC cathode showed lower performance than for CO ₂ electrolysis, due to insufficient steam content at a feed of 20% H ₂O-5% H ₂/Ar (10 ml/min) and CO ₂/CO 70/30 (20 ml/min) mixture.