Ammonia synthesis from nitrate reduction by the modulation of a built-in electric field and external stimuli

Abstract

Ammonia (NH₃) is a vital chemical feedstock and a carbon-free energy source. The reduction of nitrate (NO₃⁻) from environmental pollutants is a sustainable method for NH₃ production compared with the industrially intensive Haber–Bosch method, which can mitigate energy and environmental concerns. However, due to the involvement of multi-electron transfer-proton coupling processes, the NO₃⁻ reduction reaction (NO₃RR) exhibits sluggish kinetics and significant side reactions. This review provides a comprehensive summary of recent research progress in facilitating NO₃RRs using a built-in electric field and external stimuli. The paper commences by introducing the mechanisms and challenges of the NO₃RR, subsequently focusing on strategies for built-in electric field/external stimuli-assisted catalytic reactions. The internal electric field can be triggered by constructing a Mott–Schottky heterojunction and a semiconductor–semiconductor heterojunction, adjusting the coordination environment of active sites, and regulating the electrical double layer, while the external stimuli include optical, stress, and thermal stimuli. This review focuses on the activation and adsorption processes of reactants and intermediates by a built-in electric field/external stimuli, and their influence on the thermodynamics and kinetics of reactions. Finally, we summarize the strategies for built-in electric field/external stimuli-assisted NO₃RRs, highlight the challenges of achieving high activity and selectivity in NH₃ production, and provide clear guidance for future research.