Mechanistic Insights into KCl-Induced Water Disordering for Efficient Ammonia Electrosynthesis

Abstract

The electrocatalytic nitrite reduction reaction (eNO2–RR) presents an extraordinary surge in clean yet green ammonia (NH3) synthesis due to mild operation and its promising compatibility with renewable energy sources. Nevertheless, the sluggish NO2– reaction kinetics and the competing hydrogen evolution reaction (HER) remain challenging for efficient NO2–-to-NH3 electrosynthesis. Herein, we reveal a strong dependence of H2O structure on KCl concentration in the electrolyte and decouple the KCl-induced water disordering mechanism for efficient NH3 electrosynthesis. This disrupts the hydrogen-bond network of H2O and increases the proportion of K+-H2O species, thereby transforming an ordered proton-hopping network into a disordered environment. This ordering-to-disordering transition increases the activation entropy and lowers the activation enthalpy, leading to a reduction in the apparent free energy and enabling a 2.9-fold enhancement in NH3 production compared to the conventional electrolyte. The KCl–water electrolyte exhibits an exceptional NH3 yield rate of 111.3 mg cm–2 h–1, a Faradaic efficiency of 99.6% at −0.5 V vs RHE, and stable operation for over 1000 h at 1 A cm–2. Multiscale theoretical simulations further confirm that the K+ ions suppress the HER by elevating the water dissociation barrier from 0.1 to 0.7 eV, while the Cl– ions lower the *NO-to-*NOH hydrogenation barrier, thereby promoting the eNO2–RR kinetics. Moreover, the proposed KCl-induced H2O disordering mechanism for efficient eNO2–RR is universal, delivering consistent performance gains across various catalysts.