A cathode for a liquid fuel cell, which is covered with a film that is a liquid fuel barrier, but is permeable to oxygen, or for a direct methanol fuel cell, which is covered with a film that is a methanol barrier, but is permeable to oxygen. The fuel barrier may be made of the polymer of a macrocyclic compound having, in the same molecule, preferably three substituents that allow polymerization and crosslinking. The methanol barrier may be made of a polymerized porphyrin, wherein the porphyrin is chosen from among non-metallated and metallated porphyrins.