Long-Term Operational Performance Degradation and Thermal Stability Assessment of Direct Ammonia Sofcs Considering Ni Coarsening Effects

Abstract

Anode morphology evolution caused by Ni coarsening is one of the primary factors contributing to performance decline in direct ammonia solid oxide fuel cells (DA-SOFCs). In this study, a 3D dynamic multi-physics field model is developed to elucidate the mechanism by which Ni coarsening affects the operational stability of DA-SOFCs under various design conditions. By utilizing this model, the impact of fuel composition, flow configuration and operating parameters on performance degradation and thermal stability are systematically examined. The findings indicate that employing a co-flow configuration significantly improves the thermal stability of DA-SOFCs, reducing the maximum temperature gradient ((φT/φn)max) by 85.4% compared to a counter-flow design, with only a 0.98% decrease in initial power density. Increasing the output voltage and inlet flow rate enhances total power generation (Ptot), but excessive increments result in negative net heat flux and a sharp rise in (φT/φn)max. Additionally, a multi-parameter collaborative analysis for Ptot and (φT/φn)max of DA-SOFCs is conducted to delineate boundaries for efficient and safe operation. Specifically, within the temperature range of 725-760 oC, voltage window of 0.7-0.75 V and reference current density of 1.0-1.8 A cm-2, DA-SOFCs can achieve the optimization targets of power degradation ≤ 1% kh-1, Ptot ≥ 3.5 kW h cm-2 and (φT/φn)max ≤ 20 K cm-1. These findings offer valuable insights for improving the long-term stability of DA-SOFCs for practical applications.

Keywords: Direct ammonia solid oxide fuel cell, Ni coarsening, Performance degradation, Thermal stability, Numerical simulation