Co-Doped Fe₃S₄ Nanoflowers for Boosting Electrocatalytic Nitrogen Fixation to Ammonia under Mild Conditions

Compared with the Haber Bosch process, the electrochemical nitrogen reduction reaction (NRR) under mild conditions provides an alternative and promising route for ammonia synthesis due to its green and sustainable features. However, the great energy barrier to break the stable N≡N bond hinders the practical application of NRR. Though Fe is the only common metal element in all biological nitrogenases in nature, there is still a lack of study on developing highly efficient and low-cost Fe-based catalysts for N₂ fixation. Herein, Co-doped Fe₃S₄ nanoflowers were fabricated as the intended catalyst for NRR. The results indicate that 4% Co-doped Fe₃S₄ nanoflowers achieve a high Faradaic efficiency of 17% and a NH₃ yield rate of 37.5 μg·h^-1·mg^-1_cat. at -0.55 V versus RHE potential in 0.1 M HCl, which is superior to most Fe-based catalysts. The introduction of Co atoms can not only shift the partial density states of Fe₃S₄ toward the Fermi level but also serve as new active centers to promote N₂ absorption, lowering the energy barrier of the potential determination step to accelerate the catalytic process. This work paves a pathway of the morphology and doping engineering for Fe-based electrocatalysts to enhance ammonia synthesis.