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

Area of Science:

• Electrochemistry
• Green Chemistry
• Materials Science

Background:

• Electrocatalytic nitrite reduction (eNO2-RR) is a promising route for green ammonia (NH3) synthesis, compatible with renewable energy.
• Challenges include sluggish reaction kinetics and competition from the hydrogen evolution reaction (HER).

Purpose of the Study:

• To investigate the effect of electrolyte composition, specifically KCl concentration, on water structure.
• To decouple the mechanism by which KCl influences water structure for enhanced eNO2-RR.
• To improve NH3 electrosynthesis efficiency and yield.

Main Methods:

• Electrochemical experiments varying KCl concentration.
• Analysis of water structure and hydrogen-bond network disruption.
• Multiscale theoretical simulations (DFT) to probe reaction mechanisms and energy barriers.

Main Results:

• KCl concentration significantly alters H2O structure, disrupting the hydrogen-bond network and increasing K+-H2O species.
• This ordering-to-disordering transition enhances NH3 production by 2.9-fold, achieving 111.3 mg cm-2 h-1 with 99.6% Faradaic efficiency.
• K+ ions suppress HER, while Cl- ions promote eNO2-RR kinetics, confirmed by theoretical simulations.

Conclusions:

• A novel mechanism of KCl-induced water disordering effectively promotes eNO2-RR.
• The method demonstrates high efficiency, stability (>1000 h), and universality across different catalysts.
• This provides a pathway for efficient and sustainable ammonia synthesis.