Tunable Synthesis of Porous Iron Powder From Fe-Based MOFs via Shell-Protection Strategy for Enhanced N₂...

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable transformation of nitrogen (N₂) into highly valuable ammonia. However, achieving both a high ammonia yield and an Faradaic efficiency (FE) higher than 40% at practical current density remains challenging, particularly with bulk metal catalysts. Herein, we propose a shell-protection strategy to successfully prepare phase-pure iron powder from Fe-based metal-organic frameworks. Notably, the resulting iron powder exhibits good antioxidant and acid-resistant properties. As an NRR electrocatalyst, it delivers an ammonia yield rate of 120.05 µg h^-1 mg_cat. ^-1 and an FE of 43.44%-a 20-fold enhancement over commercial iron powder. The enhanced NRR activity is primarily attributed to the improved N₂-enrichment, facilitated N₂-activation, and effective suppression of the competitive hydrogen evolution. With only 3.83 wt% cobalt (Co) doping, the Co-doped iron powder achieves the substantially enhanced NH₃ yield rate of 200.50 µg h^-1 mg_cat. ^-1 with an FE of 56.34% at a high current density of 7 mA cm^-2. The combined experimental and theoretical analyses reveal that Fe vacancies are key to the adsorption and activation of N₂. This work provides a powerful guidance for developing more bulk transition metals to achieve green ammonia synthesis at a more industrial level.