Regulation of dynamic characteristics towards working fluctuation in ammonia solid oxide fuel cells for stable power generation

Abstract

Adapting to fluctuations in grid demand and fuel supply in direct ammonia solid oxide fuel cells (DA-SOFCs) is critically important yet highly challenging in hybrid energy systems. In this work, a high-resolution dynamic model was developed and validated with experiments to provide an in-depth understanding of the dynamic characteristics of tubular DA-SOFCs. The results reveal that ammonia decomposition increases complexity to the heat sources and distorts the distribution of species concentrations within the anode. Consequently, DA-SOFCs exhibit more pronounced relaxation times, current overshoot, and temperature variations under dynamic operating conditions. Enhanced thermal coupling between ammonia decomposition and electrooxidation through flow design reduces relaxation time by approximately 80% and temperature fluctuations by over 60%. A heat-transfer-based correlation is established to allow fast estimation of relaxation time. Extending the voltage ramp time to the ammonia mass transfer time substantially mitigates current overshoot. Furthermore, coordinated voltage and flow rate regulation on different time scales (seconds and minutes) enables fast and stable load tracking, effectively reducing power deviation from over 30% to less than 3%. These insights into the dynamic behavior of DA-SOFCs contribute to their flexible and durable operation in practical applications.