Abstract
The electrochemical nitrate reduction reaction (eNO(3) (-)RR) presents a sustainable solution for water pollutant management and green ammonia (NH(3)) synthesis. However, hindered by the spin-forbidden barrier, the sluggish hydrogenation kinetics of the key intermediate *NO severely limits the production of NH(3). 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 CuCo(2)O(4) through the Mn doping-driven oxygen vacancy strategy (Mn-CuCo(2)O(4-x) ). The elevated Co spin-state enhanced Co 3d (d (xz) /d (yz) /d (z (2)) )-*NO 2p asymmetrical orbital hybridization, facilitating *NO intermediate adsorption and the subsequent hydrogenation. Thanks to the Cu-Co synergistic effect enhanced via spin-state modulation, the Mn-CuCo(2)O(4-x) /graphene oxide aerogels (GAs) exhibited an attractive NH(3) yield rate of 2.14 mg h(-1) cm(-2) with a dramatic NH(3) faradaic efficiency of 98.37% at an environmentally relevant NO(3) (-) level (10 mM NO(3) (-)-N), far superior to that of Co(3)O(4)/GAs, CuCo(2)O(4)/GAs and as-reported catalysts. Moreover, the strong interfacial interaction between GAs and Mn-CuCo(2)O(4-x) suppresses structural reconstruction of Mn-CuCo(2)O(4-x) , 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.