Chemical-free closed-loop conversion of nitrate into struvite fertilizer via exsolved high-entropy perovskite electrocatalyst

Electrocatalytic nitrate reduction (NO₃RR) provides a sustainable pathway for converting nitrate into ammonia (NH₃); however, achieving a high NH₃ yield while simultaneously enabling its efficient recovery remains challenging. Herein, we develop an exsolved high-entropy perovskite oxide, La_0.9 (MnFeCoCuZn)_0.2O₃ (Ex-LMFCCZ), through in-situ exsolution of multimetallic nanoparticles. The exsolved nanoparticles, together with the enriched oxygen vacancies, create abundant active sites, resulting in an NH₃ yield rate of 5.62 mg/cm²/h, which is 2.13 times higher than that of the pristine catalyst Pr-LMFCCZ at −0.4 V vs . RHE. DFT calculations indicate that the downshifted d -band center facilitates the desorption of reaction intermediates, while the enhanced charge polarization promotes electron transfer, thereby enhancing the activity. In addition, the produced NH₃ from NO₃RR can be effectively captured as solid struvite (MgNH₄PO₄·6 H₂O). A closed-loop electrochemical system was further constructed for struvite recovery, in which NH₃ originated from NO₃RR, and both anodic and cathodic solutions dissolved waste minerals to provide PO₄^3- and Mg²⁺ without external reagents, yielding struvite with a purity of 57.9%. This integrated system achieves simultaneous nitrate removal, ammonia recovery, and nutrient recycling, offering a green and circular pathway for sustainable wastewater valorization.