Coupling single atomic iron sites with iron nanoparticles for tandem-enhanced ammonia electrosynthesis from nitrate

Electrocatalytic nitrate reduction to ammonia (NO 3 RR) opens a feasible approach to both wastewater treatment and ammonia production. However, the key catalyst materials still suffer from low activity, especially in neutral medium. Here we report that a tandem catalyst obtained by coupling atomic Fe sites (Fe SA ) with Fe nanoparticles (Fe NP ) in carbon supports high-performance NO 3 RR. It can deliver a maximum NH 3 faradaic efficiency of 95.5% at −0.85 V and a high NH 3 yield rate of 4042 μg h −1 mg cat −1 at −0.9 V, ranked among the top-performing catalysts reported. The combined experimental and theoretical analyses demonstrate the synergistic effect for dual sites consisting of Fe SA and corresponding Fe NP , as well as the tandem-enhanced NO 3 RR mechanism whereby Fe SA spontaneously adsorbs and activates NO 3 to form ∗NO intermediates while Fe NP accelerates water dissociation to provide more ∗H, thus promoting the following hydrogenation process and leading to consequent tandem-enhanced NO 3 RR activity.