Multiphysics-guided optimization of tubular SOECs for high-efficiency ammonia-to-hydrogen conversion

Ammonia solid oxide electrolysis cell (NH3-SOEC) offers a direct route for converting ammonia into hydrogen with high yield and without downstream purification, making it attractive for renewable energy storage and on-site hydrogen supply. However, its coupling mechanisms remain unclear, limiting improvements in hydrogen production rate and efficiency. Here, we developed a Multiphysics model based on experimental data from a tubular NH3-SOEC. Results reveal that moderate voltages enhance reaction, transfer rates, and local temperature, leading to improved performance and efficiency. Under reference conditions, the ammonia conversion, fuel utilization, and electrolysis efficiency reached 63.6%, 44.3%, and 42.0%, respectively. High-voltage operation or adjusting parameters related to cathode gas have limited effects on efficiency, yet reducing ammonia flow rate notably improves efficiency with only slight performance loss. Moreover, scaling up the cell size led to uneven hydrogen distribution. This issue was mitigated by adjusting the cell geometry: doubling the length and halving the radius improved the performance from −0.46 to −0.50 A cm−2 at 750 °C and 0.6 V. Further ammonia flow rate adjustment raised efficiencies to 93%, 74%, and 62% with only ∼3.4% loss in performance. Finally, a quantitative relationship among cell geometry, ammonia flow rate, and performance was established. This work offers mechanistic insight and design guidance for integrating NH3-SOEC into renewable ammonia-based hydrogen systems.