Enrichment and electroreduction of ultra-low nitrate to ammonia via ZnO pore confinement and built-in electric field

An interfacial catalyst with porous ZnO and Cu is constructed to promote electroreduction of ultra-low NO 3 − to NH 3 . • Porous ZnO/Cu catalyst exhibits high selectivity and conversion rate for NH 3 under ultra-low NO 3 − conditions. • The charge redistribution between ZnO and Cu creates a interface comprising electron-deficient ZnO and electron-rich Cu. • The interface improves the enrichment and adsorption of NO 3 − , and accelerates hydrogenation steps for NH 3 formation. Electrochemical nitrate (NO 3 − ) reduction offers a sustainable route for green ammonia (NH 3 ) synthesis. However, in practical wastewater treatment scenarios, low NO 3 − concentrations typically compromise NH 3 selectivity and lead to the accumulation of toxic nitrite as a by-product. Herein, we demonstrate that the synergistic catalysis arising from the ZnO/Cu interfacial structure, combined with confinement effects, enhances NH 3 selectivity in low-concentration NO 3 − reduction. The work function difference drives electron transfer from porous ZnO to Cu at the interface, generating electron-deficient ZnO sites and electron-rich Cu sites. The electron-deficient nature of porous ZnO, coupled with the confinement effect of its porous structure, facilitates the enrichment and adsorption of NO 3 − reactants. The adjacent electron-rich Cu sites promote electron–proton transfer, accelerating the hydrogenation steps in the NO 3 − -to-NH 3 pathway. This interfacial electronic configuration allows ZnO/Cu to deliver outstanding performance in a 200 ppm nitrate solution, achieving an NH 3 Faradaic efficiency of 91.9% and an NH 3 yield of 11.5mmol h −1 cm −2 at −1.0 V vs. RHE. The catalyst also reaches a NO 3 − -to-NH 3 conversion rate of 96.4%, demonstrating its dual capability for nitrate-containing wastewater purification and green NH 3 production. Download: Download high-res image (132KB) Download: Download full-size image