Nitrogen-based fertilizer recovery from nitrate wastewater: A novel electrocatalyst for ammonia synthesis and a new strategy for ammonia absorption

Electrochemically upcycling wastewater nitrogen, such as nitrate (NO₃^–-N), into a nitrogen fertilizer (e.g., (NH₄)₂SO₄), holds promise for wastewater treatment and resource recovery. However, two challenges remain: finding an efficient catalyst for electrocatalytic NO₃^–-N reduction into NH₃ (NO₃RR) and developing a suitable strategy for subsequent NH₃ separation and recovery. In this study, a high-entropy perovskite oxide, La(MnFeCoCuZn)_0.2O₃ (LMFCCZ), was synthesized and applied for NO₃RR, illustrating excellent performance with an NH₃ yield rate of 1.5 ± 0.04 mg/(cm²·h) and a FE of 95.0 ± 1.53 % at a potential of −1.1 V vs. RHE. Furthermore, a novel strategy of using acidic anolyte instead of external acid to provide H⁺ ions for NH₃ separation and recovery was introduced. As a result, paired electrolysis was fully employed to recover nitrogen-based fertilizer from NO₃^–-N without any chemicals addition. Specifically, when acidic anolyte containing 50 mM K₂SO₄ was served as the absorption liquid, the NH₃ recovery efficiency reached 70.9 ± 3.0 %, and a solid powder containing both nitrogen (N) and potassium (K) was obtained, suggesting the formation of N-K compound fertilizer. This study not only extends the application of high-entropy perovskite oxides in NO₃RR but also opens a novel avenue for utilization of anodic reactions for nitrogen-based fertilizer recovery.