A process for forming an electrolyte for a metal-supported solid-oxide fuel cell, the process comprising: a. applying a doped-ceria green electrolyte to an anode layer; b. removing any solvents and organic matter from the green electrolyte; c. pressing the green electrolyte to increase green electrolyte density; and d. heating the green electrolyte at a rate of temperature increase whilst in the temperature range 800° C.-1000° C. of in the range 5-20° C./minute to form the electrolyte, together with an electrolyte obtained by the process, a fuel cell and fuel cell stack, comprising the electrolyte, and the use of the fuel in the generation of electrical energy.