Innovative Fe-F-Co-doped NiO nanoarrays: Pioneering high-efficiency electrochemical nitrate reduction to ammonia

An efficient and long-lasting electrocatalyst was created for the electrocatalytic NITRR (nitrate reduction reaction) through a well-controlled hydrothermal process, followed by annealing. The catalyst consists of Fe, F-co-doped nickel oxide nano-arrays (Fe-F-NiO NNAs) uniformly prepared to offer high conductivity and many active sites for efficient nitrate-to-ammonia conversion. The analysis results verified the synthesis of the nanostructured Fe-F-NiO NNAs and demonstrated synergy attributed to the mutual contribution of Fe and F co-doping. Fe doping enhances the transfer of charges and active site density, resulting in an effective ion interface and reduced energy barriers. In contrast, F doping promotes the binding of intermediates and facilitates the final desorption of the product. The synergistic effects are reflected in the enhanced selectivity up to 99.9 % and efficiency in ammonia synthesis during the nitrate reduction reaction (NITRR), yielding 20.9 mmol/h.cm² of NH₃ and a Faradaic efficiency of 82.5 % under an applied potential of −1.198 V vs. RHE. Furthermore, the Fe-F-NiO NNAs showed an extended stability (36 h). Isotope tracer experiments ensured that the sensed ammonia exclusively resulted from nitrate reduction. The fabricated Fe-F-NiO NNAs functioned as a capable electrocatalyst for purifying nitrate-laden wastewater, enabling efficient NH₃ extraction.