TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The microstructure of the first layer is different from the microstructure of the superimposed layer in contact with the first layer. The elements (L) and (M) are the same for all the layers of the electrode. The first layer comprises a mixed oxide (I) with the condition that n-x is not equal to 1 and (n+1-x)/(n-y) is less than 2. The first layer is constituted of a mixed oxide of formula LNiO3, L2-xNiO4-s or L3Ni2O10-s. The first layer is made up of elementary solid particles linked to each other, the average size of these elementary particles are less than 300 nm. The thickness of the first layer is less than 200 nm, particularly around 50 nm. The last layer is made up of elementary solid particles forming open pores between them and constituting an interconnected network of solid material through its thickness. The last layer is made up of elementary solid particles linked to each other, the average size of these elementary particles being 100 nm to 5 mu m. The electrode comprises 2-5 piled layers on the solid substrate, and the different stacked layers have a total thickness of 1-15 mu m. The first layer has a porosity of less than 10 vol.%. The last layer has a porosity of greater than 10 vol.% and less than 50 vol.%. The first layer has high ionic conductivity. The first layer is made of a material of which the ionic conductivity is greater than or equal to 10-2 S.cm-1.The last layer is made of a material of which the ionic conductivity is greater than 10-4 S.cm-1 and electronic conductivity greater than 50 S.cm-1. The solid substrate is a gas proof solid electrolyte comprising conductive ceramics of oxygen (O2-) anions and proton conductive ceramics. The gas electrode in the electrochemical cell is totally flat or of cylindrical shape, particularly rotating cylinder.L = La, Pr or Nd.Preferred Process: The layers are obtained from a deposit comprising slurry deposit, charged sol deposit and sol-gel deposit. The intermediate layer between the first layer and the last layer is obtained by slurry deposition and a charged sol deposition. The first layer is obtained from a sol-gel deposition. The last layer (4) is obtained by slurry deposition or charged sol deposition. The first layer is deposited on a solid substrate by sol-gel deposition comprising mixing a precursor species in a solvent to form a mixed oxide, mixing suspension in an organic polymer matrix, applying applies the mixture on the solid substrate and subjecting the set to heat treatment for crystallization of each mixed oxide and decomposition of the organic polymer matrix. The final layer is applied either by slurry deposition comprising preparing a slurry containing solid particles of a mixed oxide dispersed in a liquid medium, applying the slurry in the form of a layer and subjecting the set to heat treatment for evacuating the liquid medium or charged sol deposition comprising dispersing the solid particles in a liquid solution of precursor species to form a mixed oxide, applying the suspension in the form of a layer and subjecting the set to a treatment for crystallizing the mixed oxides and evacuating the liquid phase. The solid substrate is deposited between two and five layers having a total thickness of 1-15 mu m. EXAMPLE - No suitable example given.