A solid oxide fuel cell (10) comprises an anode electrode (12), a cathode electrode (14) and an electrolyte (16) between the anode electrode (12) and the cathode electrode (14). A gaseous fuel is supplied to an anode chamber (18) partially defined by the anode electrode (12) and a gaseous oxidant is supplied to a cathode chamber (20) partially defined by the cathode electrode (14). The electrolyte (16) comprises a first dense non-porous layer (22), a second porous layer (24) on the first dense non-porous layer (22) and a third dense non-porous layer (26) on the second porous layer (24). The anode electrode (12) is arranged on the first dense non-porous layer (22) and the cathode electrode (14) is arranged on the third dense non-porous layer (26). The second porous layer (24) acts as a buffer between the first dense non-porous layer (22) and the third dense non-porous layer (26) to prevent defects propagating between the layers (22,26) and to prevent fuel and oxidant leaking through the electrolyte (16).