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 H2. 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.