Mechanistic insights into Mg(OH)2-driven interfacial microenvironment engineering for stabilizing intermediate adsorption configuration toward enhanced electrocatalytic ammonia synthesis from nitrate

Electrochemical nitrate reduction reaction (NO 3 RR) is an energy efficient and environmentally friendly technology that removes nitrate compounds from wastewater while producing ammonia as a value-added product. NO 2 − is a crucial intermediate in the electrocatalytic NO 3 RR, and regulating the intermediate adsorption structure is the key to improve the reaction efficiency. However, stabilizing the reaction intermediates by optimizing the catalyst structure remains a great challenge. Herein, We demonstrate copper phthalocyanine (CuPc) anchored on a Mg(OH) 2 -decorated nitrogen-doped carbon composite as an efficient electrocatalyst for NO 3 RR, achieving ambient conditions ammonia synthesis in neutral electrolytes. The incorporation of Mg(OH) 2 induces interfacial electron transfer, creating a charge-redistributed Cu active site that facilitates the adsorption of NO 3 − and reaction intermediates. Moreover, the Mg 2+ sites with negative electrostatic potential (ESP) interact with the oxygen sites exhibiting positive ESP on the critical NO 3 RR intermediate, thereby optimizing the adsorption geometry while enhancing both the stability of the intermediate and its subsequent catalytic conversion. When used for electrochemical NO 3 − reduction reaction (NO 3 RR), the developed CuPc/Mg(OH) 2 /NC exhibits a prominent Faradaic efficiency for NH 3 formation (FE NH3 ) of 98.09 % and NH 3 yield of 12.632 mg h −1  cm −2 .