Asymmetrically Cu-O-Cu bridged dual-atom sites on bio-functionalized oxides for molecular nitrate upcycling

초록

The electrochemical nitrate reduction reaction (NO3RR) is a promising strategy for decentralized ammonia (NH3) production and environmental remediation under ambient conditions. However, achieving complete eight-electron/nine-proton (8e(-)/9H(+)) conversion of NO3- to NH3 with high selectivity and efficiency remains challenging owing to sluggish NO3- activation and competing N-N coupling side reactions such as N-2, N2O, and NO gas evolution. Herein, we report a rationally designed Cu dual-atom (DA) catalyst composed of asymmetrically coordinated Cu atomic pairs anchored on an L-tryptophan-functionalized Fe3O4/alpha-Fe2O3 heterostructure (Cu-2/try-FeOx), synthesized via a CO2 laser irradiation method involving multi-step continuous-wave exposure for interface engineering. The hybrid Cu-2/try-FeOx support provides abundant N and O coordination sites and enhanced electron mobility, enabling spatially separated Cu atom by asymmetrically coordinated Cu-N/O dual sites exhibit synergistic electronic interactions, forming robust DA configurations. In situ and ex situ spectroelectrochemical analyses, supported by theoretical calculations, confirm a & lowast;NO3 -> & lowast;NO2 -> & lowast;NO -> & lowast;NHO -> & lowast;NH2O -> & lowast;NH3 -> NH3 reaction pathway. At the optimal potential, the total Faradaic efficiency toward NH3 and NO2- approaches similar to 95%, indicating effective suppression of competing H-2, N-2, and N2O formation and confirming a highly selective 8e(-)/9H(+) NO3RR mechanism. Notably, NO3RR tests using Cu-2/try-FeOX achieve a high NH3 yield rate of 0.29 mmol h(-1) cm(-2) and a maximum Faradaic efficiency of 88.5% at -0.2 V vs. RHE. Furthermore, when integrated into a Zn-NO3- battery, the catalyst enables self-powered NO3- to NH3 conversion with stable operation over 100 h. This study presents a rational approach that integrates DA site engineering catalyst design with bio-functional support design to regulate intermediate adsorption and electron transfer, thereby enhancing the activity and selectivity for self-powered molecular NO3- upcycling technologies.

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