Characterization of direct-ammonia solid oxide fuel cells (DA-SOFCs) at 650–750 °C in a single-repeating unit stack: Effects of metallic components and residual ammonia

Abstract

Ammonia can be directly utilized in solid oxide fuel cells, known as direct-ammonia solid oxide fuel cells (DA-SOFCs), which are among the most efficient technologies for ammonia utilization. Current research efforts are directed towards lowering the operating temperatures of DA-SOFCs by incorporating additional catalysts. However, critical analyses regarding the extent of ammonia decomposition on metallic interconnects and Ni current collectors, as well as the negative effect of residual ammonia on performance, are lacking. In this study, we examine DA-SOFCs with a single-repeating unit stack on a small scale, addressing the effects of metallic interconnects and the Ni-current collector on DA-SOFC operation within the temperature range of 650 °C–750 °C. The anode components, including the metallic interconnect, Ni-current collector, and the SOFC cell, are investigated in powder form and in DA-SOFC operation to determine each component's influence under actual DA-SOFC operating conditions. Both Fe-rich and Ni-rich high-temperature alloys demonstrate high catalytic activity for the ammonia decomposition reaction, playing a significant role in actual cell operations. Furthermore, extensive impedance analysis of DA-SOFC operation under various fuel conditions reveals that residual ammonia significantly increases polarization resistance at lower temperatures, which is the primary factor contributing to negative effect on performance at these temperatures.