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This study explores impact of novel parallel S-type flow channels on ammonia decomposition and thermal-electric performance of direct ammonia solid oxide fuel cells (DA-SOFC). Four channel arrangements were numerically studied using single cell models: conventional unbent channels (UC–SOFC) and proposed single S-type channels (SSC–SOFC), double S-type channels (DSC-SOFC), triple S-type channels (TSC-SOFC). Cells with parallel S-type channel configurations outperformed unbent channel. Particularly, TSC-SOFC demonstrated the highest electrical performance, followed by DSC-SOFC, SSC-SOFC, and UC-SOFC, with power density improvements of 33.6%, 28.9%, and 28.9%, respectively, compared to UC-SOFC. Further results show that S-type channels exhibit self-heating effects, namely heat released from electrochemical reactions in the rear supplies ammonia decomposition in the front part of channel, enhancing H 2 concentration and electrochemical reactions. Quantitatively, back-heat supplied to primary ammonia decomposition region increases by 33.3% in TSC-SOFC compared to UC-SOFC. Moreover, higher velocities in S-type channels enhance species diffusion towards rib underside, finally reducing concentration polarization and, improving power density. Besides of electrical performance, recycling waste heat from exhaust gases also improve the temperature uniformity cell, potentially benefiting the stability and lifetime of cell. [Display omitted] • Mathematical modeling of large-scale DA-SOFC single cells. • Cell performance optimization considering in-cell ammonia decomposition. • Promoting in-cell ammonia endothermic decomposition via a novel parallel S-type channel. • Both self-heating feedback and enhanced velocity toward the underside of the ribs are observed in the novel channel. [ABSTRACT FROM AUTHOR]

• Accurate process models for kW-level ammonia SOFC systems are developed. • Effect of off-gas recirculation on ammonia SOFC system is studied with energy flow diagram. • An optimization strategy by off-gas steam separation is proposed for ammonia SOFC system. • Comprehensive analyses of efficiency, power density and thermal safety are conducted. Solid oxide fuel cell (SOFC) power system fueled with the carbon-free fuel ammonia is a promising technique to reduce CO 2 in traffic and transportation sector. This study constructed zero-dimensional steady-state models for the SOFC stack and corresponding balance of plant (BOP) components, and conducted efficiency, power density and thermal safety analysis on a kW level ammonia SOFC system. The effects of off-gas recirculation strategy on system performance were firstly studied. The results show that in the basic ammonia SOFC system without off-gas recirculation, the fuel and air stream entering the afterburner are strictly determined by the stack operating parameters such as stack fuel utilization and flow rate. This makes its net electrical efficiency be not only low but also impossible to be independently and flexibly adjusted via controlling the fuel thermally consumed in the afterburner. The use of anode off-gas recirculation (AOGR) greatly improves the net electrical efficiency and operating flexibility via decoupling the system fuel utilization from the stack fuel utilization. By contrast, cathode off-gas recirculation (COGR) exhibits adverse effects, which reduces the net electrical efficiency and is not conducive to the thermal stability of the afterburner. In the end, a new system architecture design (SOFC-AOGR-SS) is proposed, which adopts both AOGR and steam separation in the anode recirculated off-gas using the vaporization cooling of liquid ammonia. The proposed system could operate at extended stack fuel utilization range of 0.67–0.80 and achieve a net electricity efficiency of 51.94–56.50% without external cooling water. Moreover, with additional external cooling water, the stack fuel utilization range and the net electricity efficiency of system could be extended to 0.58–0.80 and 51.84–57.15% respectively. [ABSTRACT FROM AUTHOR]