Ammonia is considered a promising hydrogen carrier due to its high hydrogen density and liquefaction temperature. Considering that the energy efficiency generally decreases as chemical conversion is repeated, it is more efficient to directly use ammonia as a fuel for fuel cells. However, catalysts in direct ammonia fuel cells have the critical issues of sluggish ammonia oxidation reaction (AOR) rate and poisoning of reaction intermediates. In particular, the use of precious metal as cathodic catalysts has been limited due to ammonia crossover and poisoning. In this study, we introduce Fe-based single-atom catalysts with selective activity for the oxygen reduction reaction (ORR) even in the presence of ammonia. As the Fe content increased, the single-atom structure of the catalysts changed into Fe nanoparticles or carbides. Among our Fe–N–C catalysts, FeNC-50 with a Fe loading amount of 0.34 wt% showed the highest ORR performance regardless of the ammonia concentration. In particular, the difference in activity between the catalysts increased as the concentration increased. The FeNC-50 catalyst showed remarkable stability after 1000 cycles. Therefore, we believe that single-atom dispersion is an important factor in the development of stable non-precious catalysts with high activity and inactivity for the ORR and AOR, respectively.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Synthesis of ZIF-8
        2.2 Synthesis of Fe–pNC-x
        2.3 Synthesis of FeNC-x
        2.4 Characterization
        2.5 Electrochemical measurements
    3 Results and discussion
    4 Conclusion
    References

• Han‑Wool Jang(Department of Energy Engineering, Konkuk University)
• Seon Yeong Lee(Department of Energy Engineering, Konkuk University)
• Jong Yoon Lee(Department of Energy Engineering, Konkuk University)
• Han‑Ik Joh(Department of Energy Engineering, Konkuk University)