Spatially Separated Cu/Ru on Ordered Mesoporous Carbon for Superior Ammonia Electrosynthesis from Nitrate over a Wide Potential Window

Nitrate (NO₃^-) in wastewater poses a serious threat to human health and the ecological environment. The electrocatalytic NO₃^- reduction to ammonia (NH₃) reaction (NO₃^-RR) emerges as a promising carbon-free energy route for enabling NO₃^- removal and sustainable NH₃ synthesis. However, it remains a challenge to achieve high Faraday efficiencies at a wide potential window due to the complex multiple-electron reduction process. Herein, spatially separated dual-metal tandem electrocatalysts made of a nitrogen-doped ordered mesoporous carbon support with ultrasmall and high-content Cu nanoparticles encapsulated inside and large and low-content Ru nanoparticles dispersed on the external surface (denoted as Ru/Cu@NOMC) are designed. In electrocatalytic NO₃^-RR, the Cu sites can quickly convert NO₃^- to adsorbed NO₂^- (*NO₂^-), while the Ru sites can efficiently produce active hydrogen (*H) to enhance the kinetics of converting *NO₂^- to NH₃ on the Cu sites. Due to the synergistic effect between the Cu and Ru sites, Ru/Cu@NOMC exhibits a maximum NH₃ Faradaic efficiency (FE_NH3) of approximately 100% at -0.1 V vs reversible hydrogen electrode (RHE) and a high NH₃ yield rate of 1267 mmol g_cat^-1 h^-1 at -0.5 V vs RHE. Finite element method (FEM) simulation and electrochemical in situ Raman spectroscopy revealed that the mesoporous framework can enhance the intermediate concentration due to the in situ confinement effect. Thanks to the Cu-Ru synergistic effect and the mesopore confinement effect, a wide potential window of approximately 500 mV for FE_NH3 over 90% and a superior stability for NH₃ production over 156 h can be achieved on the Ru/Cu@NOMC catalyst.