As the fuel cell is in the presence of water work, the stability of polymer water directly determines the life of the material. The stability of water in two ways: One is physical, that is, the loss of strength of the film due to swelling or even dissolution of the hydrophilic film by water. The other is chemically, i.e., the hydrolytic stability of the polyimide under battery conditions. Due to the imide ring itself on the hydrolysis, especially in alkali and strong acid in the instability, in the selection of polyimide as the exchange membrane when you need special attention. The usual five-membered ring is more sensitive to hydrolysis due to the larger ring tension, while the six-membered ring is relatively stable.