Atomic vacancy engineering of Co(OH)F nanoarray toward high-performance ammonia electrosynthesis with waste plastics upgrading

Developing energy-efficient nitrite-to-ammonia (NO₂RR) conversion technologies while simultaneously enabling the electrochemical upcycling of waste polyethylene terephthalate (PET) plastics into high-value-added chemicals is of great significance. Herein, an atomic oxygen vacancy (V_o) engineering is developed to optimize the catalytic performance of V_o2-Co(OH)F nanoarray towards the NO₂RR and PET-derived ethylene glycol oxidation reaction (EGOR). The optimal V_o2-Co(OH)F achieves an ultralow operating potential of −0.03 V vs. RHE at −100 mA cm⁻² and a remarkable NH₃ Faradaic efficiency (FE) of 98.4% at −0.2 V vs. RHE for NO₂RR, and a high formate FE of 98.03% for EGOR. Operando spectroscopic analysis and theoretical calculations revealed that oxygen vacancies play a crucial role in optimizing the electronic structure of V_o2-Co(OH)F, modulating the adsorption free energies of key reaction intermediates, and lowering the reaction energy barrier, thereby enhancing its overall catalytic performance. Remarkably, the V_o2-Co(OH)F-based NO₂RR||EGOR electrolyzer realized high NH₃ and formate yield rates of 33.9 and 44.9 mg h⁻¹ cm⁻² at 1.7 V, respectively, while demonstrating outstanding long-term stability over 100 h. This work provides valuable insights into the rational design of advanced electrocatalysts for co-electrolysis systems.