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.