Abstract: This invention pertains to a fuel cell which comprises a case, positive and negative electrodes inserted therein and electrolyte filling the inner space between the electrodes. Means for introducing an oxidizing gas into the space behind one electrode and a fuel behind the other are provided. A porous membrane substantially parallel to the electrodes comprising a self-supporting compressible porous fibrous mat of randomly dispersed and entangled micro-fibers of a high molecular weight thermoplastic polymer impregnated with said electrolyte occupies said inner space. This porous membrane permits communication of electrolyte between electrodes but prevents passage of small bubbles of oxidizing or fuel gases.