The role of input gas species to the cathode in the oxygen-ion conducting and proton conducting solid oxide fuel cells and their applications: Comparative 4E analysis

Most of the gas species in the air entering the fuel cell through the cathode electrode is nitrogen. Nitrogen recognizes as the only reactant inside the fuel cell stack that remains unchanged during its internal chemical and electrochemical processes. Owing to this specific behavior of nitrogen, this study investigates the performance of two types of solid oxide fuel cells with different electrolytes (oxygen-ion conducting and proton conducting) and their electricity generation applications under the influence of changes in nitrogen ratio of the air entering the cathode electrode. Also, the role of simultaneous changes in nitrogen ratio with two main fuel cell design parameters, precisely, current density and fuel utilization factor, on the performance of the fuel cell is scrutinized. Moreover, this study compares the performance of two different electrolytes in the fuel cell structure and their application under identical conditions from thermodynamic, economic, and environmental prespectives. According to the results, with increasing input nitrogen ratio, the voltage output of each cell, energy and exergy efficiencies, electricity generation rate, and exergoeconomic factor of the applications decrease, while the unit cost of electricity and carbon dioxide emission increase. The sensitivity of the reduction in performance is higher in nitrogen ratios above 0.7.