Design of ammonia oxidation electrocatalysts for efficient direct ammonia fuel cells

In the past few decades, renewable-energy-driven fuel cell technologies have been widely investigated as promising approaches to alleviate the energy and environmental crisis caused by fossil fuel consumption. Similar to hydrogen, ammonia provides a potential solution due to its comparable energy density and carbon-free emissions. Besides, the convenient storage and transportation of ammonia make the direct ammonia fuel cell (DAFC) a more secure technology than the hydrogen-based fuel cell system. However, the sluggish kinetics of ammonia oxidation reaction significantly hindered the performance of low-temperature DAFCs, urgently demanding systematic guidance for designing high-efficiency electrocatalysts. In this review, with an in-depth study of the basic principle of DAFC and the mechanism of AOR, we systematically summarized and discussed the recently reported strategies for developing high-performance AOR electrocatalysts, including size regulating, crystal facet engineering, morphology controlling, defect engineering, alloying, heterostructure constructing, and molecular engineering strategies. Finally, we propose perspectives and challenges for future AOR electrocatalyst development and high-performance DAFC construction. We hope this review could provide significant insights into fabricating active and stable AOR electrocatalysts for practical low-temperature DAFC.