Temperature gradient reduction in a tubular direct ammonia solid oxide fuel cell by fluidizing the cathode particles

Abstract

Thermal management is critical for the direct ammonia solid oxide fuel cell (DA-SOFC) to improve its stability and reliability. In this study, we proposed a DA-SOFC by fluidizing the cathode particles to decrease the axial temperature gradient. The results show that the non-uniform endothermic ammonia decomposition and exothermic electrochemical reactions contribute to the high axial temperature gradient, leading to a high axial thermal stress difference (8.8 MPa) between the cathode and electrolyte in the tubular DA-SOFC. Obvious de-lamination of the cathode from the electrolyte was observed at such a high thermal stress difference. Fluidizing the cathode particles significantly enhances the axial heat transfer, thus reducing the temperature gradient in the cathode chamber. Due to the low thickness (∼650 μm) and high heat transfer coefficient (11 W m⁻¹ K⁻¹) of the tube, heat can be efficiently transferred from the cathode chamber to the tube and anode chamber. The decreased temperature gradient in the cathode chamber can also decrease the temperature gradient in the tube and anode chamber. Therefore, fluidizing the cathode particles decreases the maximum temperature gradient from 22.7 °C cm⁻¹ to 10.5 °C cm⁻¹. The maximum axial thermal stress difference between the cathode and electrolyte is decreased to 4.0 MPa. Therefore, the micro-structure and electrochemical performance remain over 200 h. This work helps to deepen our understanding of the thermal management in the DA-SOFC through axial temperature gradient reduction and improves operational reliability.