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

Electrocatalytic nitrate reduction to ammonia (NO3RR) 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 (FeSA) with Fe nanoparticles (FeNP) in carbon supports high-performance NO3RR. It can deliver a maximum NH3 faradaic efficiency of 95.5% at −0.85 V and a high NH3 yield rate of 4042 μg h−1 mgcat−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 FeSA and corresponding FeNP, as well as the tandem-enhanced NO3RR mechanism whereby FeSA spontaneously adsorbs and activates NO3 to form ∗NO intermediates while FeNP accelerates water dissociation to provide more ∗H, thus promoting the following hydrogenation process and leading to consequent tandem-enhanced NO3RR activity.