Synergistic effect of Cu and Cu+ sites in MOF-derived coral-like heterostructures for efficient electrocatalytic reduction of nitrate to ammonia

The electrochemical nitrate reduction reaction (NO 3 RR) offers a sustainable route for ammonia synthesis and wastewater remediation, yet developing efficient and stable electrocatalysts remains challenging. Herein, we report a high-performance heterostructured electrocatalyst, Cu-Cu 2 O@C-350, derived from controlled pyrolysis of a Cu-BTC metal-organic framework. Calcination at 350 °C transforms the precursor into a three-dimensionally interconnected coral-like carbon architecture embedded with Cu/Cu 2 O heterojunctions, exposing abundant active sites and facilitating mass transport. The optimal catalyst exhibits exceptional NO 3 RR performance, achieving a high ammonia yield of 46.63 mg h −1 mg cat −1 and a Faradaic efficiency of 98.43% at −0.7 V vs. RHE. In situ Raman spectroscopy reveals the synergistic mechanism that metallic Cu sites initiate nitrate reduction to nitrite, while Cu + sites facilitate deep hydrogenation of nitrite to ammonia. Density functional theory calculations demonstrate that the built-in electric field at the Cu-Cu 2 O interface induces directional electron transfer from Cu to Cu 2 O, optimizing intermediate adsorption and lowering the kinetic barrier. Finally, a rechargeable Zn-NO 3 battery with Cu-Cu 2 O@C-350 as the cathode delivers a peak power density of 2.07 mW cm −2 , highlighting its potential for practical energy conversion. This work provides valuable insights into the rational design of MOF-derived heterostructured electrocatalysts for efficient electrocatalytic reactions.