Promoting Active Hydrogen Supply and Nitrate Adsorption by Disordering Tetrahedral-Octahedral Structure of CuAl₂O_4-δ for Efficient Nitrate Reduction.

Abstract

Modulating the local coordination environment can optimize the electronic structure and reaction pathway of nitrate reduction to ammonia (NO₃RR), beneficial to enhance the catalytic activity and selectivity. Herein, a disordered tetrahedral-octahedral structure of CuAl₂O_4-δ (CAO) is proposed by Co doping as an efficient catalyst. Theoretical calculations reveal Co doping induces strong Co-Al orbital interactions at octahedral sites, which lowers the energy barrier for water dissociation, and meanwhile, Oxygen vacancies (Vos) induced by Co doping not only enhance NO₃ ^- adsorption, but also serve as reservoir sites for transient ^*H storage, thereby promoting hydrogenation steps. The synergistic Cu-Vo interaction facilitates the conversion of ^*NO₃ ^- to ^*NO₂ ^- and the interfacial electron transfer between Co and Cu suppresses the hydrogen evolution reaction (HER). The substitution of 30% Co in CAO (Co-3) nanofibers creates the most Vos, resulting in a high Faradaic efficiency (FE) of 92.00% and a substantial NH₃ yield rate of 27.86 mg h^-1 mg^-1 _cat. in neutral media. Additionally, it exhibits exceptional long-term electrochemical durability and chemical stability. Thermodynamic analysis unveils the potential-determining step of ^*NO₂ to ^*NO for Co-3 possesses a low free energy of only 0.05 eV, highly superior to 0.29 eV for the pristine CAO.