Pyrochlore La₂Zr_2–xNi_xO₇ anodes for direct ammonia solid oxide fuel cells

Abstract

Developing efficient anode catalysts for direct ammonia solid oxide fuel cells (NH₃-SOFCs) under intermediate-temperatures is of great importance, in support of hydrogen economy via ammonia utilization. In the present work, the pyrochlore-type La₂Zr_2–xNi_xO_7+δ (LZN_x, x = 0, 0.02, 0.05, 0.08, 0.10) oxides were synthesized as potential anode catalysts of NH₃-SOFCs due to the abundant Frankel defect that contributes to the good conductivity and oxygen ion mobility capacity. The effects of different content of Ni²⁺ doping on the crystal structure, surface morphology, thermal matching with YSZ (Yttria-stabilized zirconia), conductivity, and electrochemical performance of pyrochlore oxides were examined using different characterization techniques. The findings indicate that the LZN_x oxide behaves as an n-type semiconductor and exhibits an excellent high-temperature chemical compatibility and thermal matching with the YSZ electrolyte. Furthermore, LZN_0.05 exhibits the smallest conductive band potential and bandgap, making it have a higher power density as anode material for NH₃-SOFCs compared to other anodes. As a result, the maximum power density of the LZN_0.05-40YSZ composite anode reaches 100.86 mW/cm² at 800 °C, which is 1.8 times greater than that of NiO-based NH₃-SOFCs (56.75 mW/cm²) under identical flow rate and temperature conditions. The extended durability indicates that the NH₃-SOFCs utilizing the LZN_0.05-40YSZ composite anode exhibits a negligible voltage degradation following uninterrupted operation at 800 °C for 100 h.

Graphical abstract

Keywords

anode catalyst / ammonia oxidation / Ni particles / NH₃-SOFCs

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 22378069, 22278081, and 22308055), the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No. 22221005), the National Key R&D Program of China (Grant Nos. 2022YFB4003701 and 2022YFB4002404), the Natural Science Foundation of Fujian Province, China (Grant Nos. 2023J01066 and 2022J05027), the Talent Program of Fuzhou University (Grant No. XRC-22036).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11708-024-0948-2 and is accessible for authorized users.

Competing Interests

The authors declare that they have no competing intererts.

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