Steam electrolysis is one of the most efficient approaches for producing green hydrogen. The method is based on the application of solid oxide electrolysis cells (SOECs) fabricated by functional ceramic composites for water splitting at high temperatures. Gadolinium doped ceria (GDC) is a promising electrolyte material for the fabrication of SOECs. However, the effective sintering temperature for GDC composite is usually above 1250 °C, which makes it impossible to use conventional supporting materials like ferritic steels for stack fabrication. In this work, for the first time, we have developed a lithium bismuth-copper co-doped GDC composite capable of sintering at ~750 °C. The physicochemical and electrochemical characteristics of the co-doped GDC electrolyte were systematically analysed using thermogravimetric analysis (TG/DTA), Raman spectroscopy, SEM/EDX, XRD, EIS, XPS and dilatometry analysis. The fabricated electrolyte pellets sintered at 750 °C for 6 hours in an inert atmosphere (argon) showed high densification, obtaining 96.70 % relative density. Also, the electrical conductivity obtained for the synthesised composite Ce0.712Gd0.178Li0.05Bi0.05Cu0.01O1.801 (sintered at 950 °C 6h) was 29.6 mS.cm-1 at 750 °C with activation energy as low as 0.13 eV. The result of this study helps to understand better the properties of co-doped electrolyte materials for the fabrication of more efficient steam electrolysers for environmentally-friendly hydrogen generation.