Abstract: The invention provides an improved method for producing cathode diffusion barrier layer, and a SOFC with high efficiency and longevity. It comprises depositing a pure ceria or aliovalently doped ceria layer, by ALD, on the electrolyte layer of the sintered half cell. The surface of a electrolyte onto which film is to be deposited is exposed to a dose of vapor from one or more lanthanide first precursors. Any excess of unreacted vapor from that precursor is removed. Next, a vapor dose of the second precursor is brought to the surface and allowed to react. A second purge completes the ALD cycle, which is repeated to build up thicker films. This ceria layer forms a cathode diffusion barrier layer on top of which a cobaltite based cathode layer is applied by screenprinting, and the cathode diffusion barrier layer and cathode layer are heated together to form a SOFC.