NOVELTY - A catalyst coated membrane (CCM) comprises a membrane having on one of the two surfaces a first electrocatalytic layer containing a catalyst and on the other one a second electrocatalytic layer containing a catalyst. The orthogonal projection of the perimeter of the first electrocatalytic layer on the second layer is distant from the perimeter of the second electrocatalytic layer at least 1 (preferably 2) mm. The electrocatalytic layers and the membrane containing (per)fluorinated ionomers.    USE - In the preparation of catalyst coated membrane; in electrochemical cells e.g. fuel cells (claimed) and electrochemical device.    ADVANTAGE - The catalyst coated membrane shows an improved adhesion among the layers and very limited size variations in the two orthogonal directions of the plane xy such as lower than 15 (preferably lower than 10)%; remains unchanged after subjected to treatments of 60 cycles by dipping in water at 80degreesC for 8 hours and then in water at 25degreesC for 16 hours; good mechanical resistance on the electrocatalytic layer edges; shows the same size variation in the two orthogonal directions of the plane xy as no delamination takes place among the layers; improves catalyst coated membrane duration in electrochemical cell, in particular with improved resistance to the catalyst coated membrane breaks; shows high dimensional stability. The catalyst coated membrane is obtained by the process eliminates the coupling of unsupported membranes.    DETAILED DESCRIPTION - A catalyst coated membrane (CCM) comprises a membrane having on one of the two surfaces a first electrocatalytic layer containing a catalyst and on the other one a second electrocatalytic layer containing a catalyst. The orthogonal projection of the perimeter of the first electrocatalytic layer on the second layer is distant from the perimeter of the second electrocatalytic layer at least 1 (preferably 2) mm. The electrocatalytic layers and the membrane containing (per)fluorinated ionomers. The CCM has size variations in the orthogonal directions of the plane xy which is lower than (15, preferably lower than 10)%, after CCM dipping in demineralized water at 100degreesC for 30 minutes, dried at 105degreesC under vacuum for one hour; remains unchanged after 60 cycles by dipping in water at 80degreesC for 8 hours and then in water at 25degreesC for 16 hours. An INDEPENDENT CLAIM is included for preparation of catalyst coated membrane (CCM) involving 1) formation of the first electrolytic layer on the surface of an inert support is carried out by: 1a) preparing a first liquid dispersion containing an ionomer (0.5 - 40, preferably 0.5 - 25) wt.%, in acid or salified form, and the catalyst where the ratio by weight between catalyst and ionomer is 0.5 - 4; 1b) the dispersion prepared in step 1a) is placed on the surface of an inert support; 1c) removal of the solvent (80 wt.%) to obtain a first electrocatalytic layer having an extractable ionomer (greater than or equal to 80, preferably up to 100) wt.%; and a catalyst amount in electrocatalytic layer is 0.01 - 2 mg/cm2; 2) on the first electrolytic layer formation of the ionomeric membrane is carried out by: 2a) preparation of a liquid dispersion containing an ionomer in acid or salified form and having a concentration of 3 - 40 (preferably 7 - 25) wt.%; 2b) the liquid dispersion obtained in step 2a) is placed on the free surface of the first electrocatalytic layer; 2c) solvent removal for at least 80 wt.% as step 1c), obtaining an ionomeric membrane on the top of the first electrocatalytic layer; the ionomer % extractable after this step is greater than or equal to 80 (preferably up to 100) with respect to the total ionomer present in the first catalytic layer and the membrane; 3) formation of the second electrolytic layer on the surface of the ionomeric membrane free from the catalyst to obtain the raw catalyst coated membrane (CCM) on the inert support is carried out by: 3a) preparation of a second liquid dispersion comprising an ionomer (0.5 - 40, preferably 0.5 - 25) wt.%, in acid or salified form, and a catalyst where catalyst/ionomer ratio is 0.5 - 4 wt.% and in the second dispersion, the ionomer and/or catalyst those used in step 1a) and step 2a); 3b) deposition of the liquid dispersion obtained by step 3a) on the surface of the ionomeric membrane free from catalyst prepared in step 2) to form the second electrocatalytic layer, positioned on the membrane so that the orthogonal projection of its perimeter on the first electrocatalytic layer is distant from the perimeter of the latter at least 1 (preferably 2) mm in each point of the projection; 3c) solvent removal from the second dispersion for at least 80% by weight which is same as in step 1c), until obtaining the second electrocatalytic layer having a catalyst amount which is same as in step 1c) and the ionomer % extractable after this step from the raw catalyst coated membrane is greater than or equal to 80 (preferably up to 100) wt.% with respect to the total weight of the ionomer present in the catalyst coated membrane (CCM); 4) annealing of the raw catalyst coated membrane (CCM) supported on the inert support at 12 - 280degreesC and obtaining catalyst coated membrane (CCM) by separation of the inert support from the catalyst coated membrane (CCM).