Electrochemical modeling of ammonia-fed solid oxide fuel cells based on proton conducting electrolyte

An electrochemical model was developed to study the NH₃-fed and H₂-fed solid oxide fuel cells based on proton conducting electrolyte (SOFC-H). The modeling results were consistent with experimental data in literature. It is found that there is little difference in working voltage and power density between the NH₃-fed and the H₂-fed SOFC-H with an electrolyte-support configuration due to an extremely high ohmic overpotential in the SOFC-H. With an anode-supported configuration, especially when a thin film electrolyte is used, the H₂-fed SOFC-H shows significantly higher voltage and power density than the NH₃-fed SOFC-H due to the significant difference in concentration overpotentials. The anode concentration overpotential of the NH₃-fed SOFC-H is found much higher than the H₂-fed SOFC-H, as the presence of N₂ gas dilutes the H₂ concentration and slows down the transport of H ₂. More importantly, the cathode concentration overpotential is found very significant despite of the thin cathode used in the anode-supported configuration. In the SOFC-H, H₂O is produced in the cathode, which enables complete fuel utilization on one hand, but dilutes the concentration of O₂ and impedes the diffusion of O₂ to the reaction sites on the other hand. Thus, the cathode concentration overpotential is the limiting factor for the H₂-fed SOFC-H and an important voltage loss in the NH₃-fed SOFC-H. How to reduce the concentration overpotentials at both electrodes is identified crucial to develop high performance SOFC-H. © 2008 Elsevier B.V. All rights reserved.