Planar Chlorination Engineering Enhances the Polarity of the Fe–N4 Site for Boosting Nitrate Electroreduction

Introducing polarity in traditional metal-N₄ catalytic sites and strengthening the adsorption of polar NO₂* intermediate are advantageous for the deep reduction of nitrate into ammonia. Herein, the planar chlorination engineering strategy successfully introduced the C–Cl bonds adjacent to the Fe–N₄ catalytic site with higher polarity, effectively boosting the catalytic activity for the nitrate reduction reaction (NO₃RR). The maximal NH₃ yield rate and the corresponding turnover frequency (TOF) value catalyzed by the Fe–N₄/CNCl catalyst were 1.82 mg h^–1 cm^–2 and 245 h^–1 at −0.83 V vs RHE, which were 3.4 times and 2.7 times those of the traditional Fe–N₄/CN catalyst without polarity, respectively. The Fe–N₄/CNCl catalyst also exhibited satisfactory stability during consecutive 15 cycles. The density functional theory (DFT) calculation revealed that the planar chlorination engineering of the Fe–N₄ site with higher polarity strengthened the adsorption of polar NO₂* intermediate, facilitated the deep reduction of nitrate into ammonia, lowered the energy barrier of rate-determining step (RDS) and thus improved the catalytic activity. This work exhibited the enormous advantage of a planar chlorination engineering strategy for enhancing the activity of electrocatalysis by introducing polarity in the traditional metal-N₄ catalytic site.