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 .