Fuel cell system using nitrogen

The present invention provides a fuel cell system using nitrogen. The system determines the operating voltage of the stack module by measuring the hydrogen concentration fed into the stack module. Therefore the stack module does not need to carry out an electrochemical reaction in the case of hydrogen deficiency, so as to avoid damage to the stack module. In addition, nitrogen gas, which does not participate in the electrochemical reaction, is mixed with the incoming fuel gas, and the operating voltage is determined on the premise of completely consuming hydrogen gas. Then, the stack module generates the maximum electric energy under the maximum reaction efficiency, and uses nitrogen as the tail gas to take away the water generated by the reaction, so as to avoid the accumulation of water in the stack module and affect the power generation efficiency.