Electron-deficient asymmetric Co centers marry oxygen vacancy for NO3RR: Excellent activity and anion resistance property

The electrocatalytic reduction of nitrate (NO₃RR) to carbon-free ammonia synthesis from wastewater offers a promising alternative for achieving nitrogen recycling. Co-based electrocatalysts often suffer from competitive hydrogen evolution reactions, especially at a high reaction potential resulting in low faradaic efficiency in NO₃RR. Herein, we constructed electron-deficient asymmetric Co centers riching Co₃O₄ nanoparticles (HP-Co) through in-situ treatment of nitrogen for hollow Co₃O₄ precursor. Such a process triggers a rational superexchange effect of the N element in the O lattice of whole Co₃O₄, rendering electron-deficient asymmetric Co centers and abundant oxygen vacancies, making the catalyst conducive to the adsorption and activation of nitrate ions. Experimental results show an excellent ammonia yield of HP-Co of 59.7 ± 1.2 mg h⁻¹ mg_cat^-1, with an exceptional maximum faradaic efficiency of 99 ± 0.5 % and a nitrate conversion rate of 95 ± 0.8 %, which outperforms most state-to-art catalysts. Impressively, such a catalyst showcases no accumulation of intermediate NO₂^– in the NO₃RR excluding the threat of secondary pollution. The mechanistic XPS study with NO atmosphere at near-atmospheric pressure approved that the Co(II) and oxygen vacancy determine the reaction progress through dominant adsorption of intermediates and participated activation. Furthermore, the theoretical calculation results reveal that the asymmetric Co centers lower the reaction carrier of the reaction-determined step that NO* intermediates over reactive sites. Interestingly, HP-Co shows stable NO₃RR performance against various anions interference by highly negative potential, coupling with excellent stability test (60 h), further highlighting its potential for practical applications.