Manipulating spin-state conversion to promote asymmetric d–p orbital hybridization for high-efficiency nitrate electroreduction to ammonia

The electrochemical nitrate reduction reaction (eNO₃ ^-RR) presents a sustainable solution for water pollutant management and green ammonia (NH₃) synthesis. However, hindered by the spin-forbidden barrier, the sluggish hydrogenation kinetics of the key intermediate *NO severely limits the production of NH₃. Here, we reported for the first time the realization of a controllable transition of the inner Co spin-state from a low spin to a high spin in CuCo₂O₄ through the Mn doping-driven oxygen vacancy strategy (Mn-CuCo₂O_4-<i>x</i> ). The elevated Co spin-state enhanced Co 3d (d _<i>xz</i> /d _<i>yz</i> /d _{<i>z</i> ²} )-*NO 2p asymmetrical orbital hybridization, facilitating *NO intermediate adsorption and the subsequent hydrogenation. Thanks to the Cu-Co synergistic effect enhanced <i>via</i> spin-state modulation, the Mn-CuCo₂O_4-<i>x</i> /graphene oxide aerogels (GAs) exhibited an attractive NH₃ yield rate of 2.14 mg h^-1 cm^-2 with a dramatic NH₃ faradaic efficiency of 98.37% at an environmentally relevant NO₃ ^- level (10 mM NO₃ ^--N), far superior to that of Co₃O₄/GAs, CuCo₂O₄/GAs and as-reported catalysts. Moreover, the strong interfacial interaction between GAs and Mn-CuCo₂O_4-<i>x</i> suppresses structural reconstruction of Mn-CuCo₂O_4-<i>x</i> , endowing the hybrid with robust stability. Herein, we confirm that spin-state modulation can enhance the Cu-Co synergistic effect and reveal a universal strategy to optimize intermediate adsorption/conversion through the spin-state, opening up a new avenue for deep purification of water pollutants based on spin optimization and providing general principles for the rational design of catalytic materials.