Water produced by the fuel cell or excess water recovered by the fuel reformer usually contains nitrogen by about 10 mol ppm. When the nitrogen-containing water is fed to the natural gas reformer or the converter which produces hydrogen, ammonia is produced by the reforming catalyst or the conversion catalyst. When the thus produced ammonia is fed to the electrode of the fuel cell together with the hydrogen gas, ammonium phosphate is produced as a result of chemical reaction between ammonia and phosphoric acid, causing the deterioration of the electrolyte. This invention solves the problem. A denitrification process is added to the steam separation/water supply system for the reforming reaction to reduce the dissolved nitrogen in water to be supplied to the fuel cell below 1 mol ppm in order to prevent the degradation of electrolyte in the fuel cell and to stabilize the output voltage of the fuel cell for a long period of time. As for the denitrification process, employing a nitrogen separation membrane, denitrifying by heating to distillation, or applying the vacuum for degassing can be used. 1 fig., 1 tab.
Tanaka, Y 
- The Tokyo Electric Power Co. Inc., Tokyo (Japan). Development and Research Lab.