Characterizing electro-thermal balance of zero-emission ammonia-fed solid oxide fuel cell systems integrated into hybrid propulsion plant for marine applications

This study develops a multi-scale coupled model including electrochemical, thermodynamic, and kinetic processes to systematically analyze the electro-thermal balance characteristics of ammonia-fed solid oxide fuel cell (SOFC) systems for marine applications. The framework resolves stack temperature fields under various operating parameters and load conditions and evaluates system running boundaries, emissions, and levelized cost of electricity (LCOE) for six electro-thermal balance schemes. Compared with previous SOFC system studies, the model explicitly links ammonia pre-cracking and anode-off gas recirculation strategies to the electro-thermal feasibility envelope and techno-economic and environmental metrics. Comprehensive analysis shows that increasing ammonia pre-cracking ratio significantly reduces stack temperature gradients and enhances thermal safety, while narrowing the operating windows for dead-end anode (DEA) loop and baseline systems and expanding that for the anode-off gas recirculation (AGR) system. The recirculation ratio also strongly influences matching performance. Specifically, the AGR system offers the widest operating range and high efficiency, the DEA system achieves the highest efficiency with zero NOx and N2O emissions, and the baseline system delivers the highest power density but exhibits lower efficiency and higher emissions. According to the entropy-weighted TOPSIS method, the best case is the DEA system, showing an LCOE of 0.652 USD/kWh, zero emissions, a maximum stack temperature gradient of 28.16 K/cm, and a running range of 0.2132. These findings establish quantitative electro-thermal balance strategies for SOFC applications across diverse marine scenarios and provide theoretical support for net-zero, high-efficiency transformation of future ship propulsion systems.