Unlocking the Critical Role of Noncovalent Interactions Between Alkali Metal Cations and Nitrate in Promoting the Reduction of Nitrate to Ammonia

The electrochemical nitrate reduction reaction (NO₃ ^-RR) is widely investigated for sustainable ammonia (NH₃) production from NO₃ ^- pollutants. Alkali metal cations (AM⁺) in the electrolyte often greatly impact electrocatalytic performance; however, the role of AM⁺ in the NO₃ ^-RR remains unclear. Here, we first investigate the influence of AM⁺ on the Cu-catalyzed NO₃ ^-RR, revealing an activity increase trend of Li⁺ < Cs⁺ < Na⁺< K⁺, which is inconsistent with the local electric field and proton transfer rate increase trend of Li⁺ < Na⁺ < K⁺ < Cs⁺, hinting that the presence of other important factors governs the NO₃ ^-RR activity. Intriguingly, Ab initio molecular dynamic (AIMD) simulations uncover that Na⁺, K⁺, and Cs⁺ with relatively soft solvation shells could be partially desolvated and then coordinate with NO₃ ^- via a short-range electrostatic interaction, thereby boosting the rate determining step (RDS), that is the conversion of NO₃ ^- to NO₂ ^-. Notably, K⁺ with suitable NO₃ ^- interaction strength has higher ability to boost the RDS than Na⁺ and Cs⁺ with too weak and strong strength, respectively. Our results highlight that the short-range electrostatic interaction strength of AM⁺/NO₃ ^- is a crucial factor to determine the NO₃ ^-RR activity.