Tandem Catalysis Driven by Nitrogen Spillover in a Core-Shell Heterostructure for Direct Ammonia Fuel Cells

Low-temperature direct ammonia fuel cells (DAFCs) are promising yet challenged by slow ammonia oxidation reaction (AOR) kinetics and severe catalyst poisoning. To address such bottlenecks, we design a vertically aligned NiCo₂O₄@NiCo₂S₄ core-shell heterostructure where the NiCo₂S₄ shell stands for NH₃ activization and the NiCo₂O₄ core serves for N₂ generation. The built-in electric field at the heterointerface, together with the bimetallic synergy introduced by Ni doping, enables the optimization of electron configuration via work function engineering. Driven by the adsorption energy gradient across heterointerface, the efficient *N spillover promotes the regeneration of NH₃ adsorption sites and facilitates the efficient desorption of N₂, leading to a refined tandem catalytic pathway of NH₃-*N-N₂. Consequently, NiCo₂O₄@NiCo₂S₄ achieves a high current density of 972 mA cm^-2 at 80 °C in a three-electrode system and delivers 20-h stability, offering a novel strategy for high-performance, poison-tolerant AOR anodes.