Fast Seawater Desalination Driven by Efficient Nitrate Reduction via Bimetallic Iron/Zinc Polyphthalocyanine Frameworks

Freshwater scarcity and nitrate contamination in water sources are critical environmental sustainability challenges. We address these two challenges by coupling seawater desalination with electrochemical nitrate reduction (NO₃RR) via bimetallic Fe/Zn polyphthalocyanine frameworks. They serve as high-performance catalysts for NO₃RR toward ammonia (NH₃) production. The efficient NO₃RR is integrated into an electrocatalytic desalination device, enabling the production of freshwater from seawater and the removal of nitrate from contaminated water. In situ spectroscopic studies and theoretical calculations show that Zn-N₄ units incorporated into the Fe polyphthalocyanine framework modulate Fe-N₄ sites' d-band center to enhance the adsorption of NO₃ ^- and the generation of *H, resulting in 3.22 times higher turnover frequency and highly selective reduction toward NH₃. The optimized Fe₈Zn₁PPc delivered NH₃ Faradic efficiency (>97% over a wide potential range (-0.55 to -0.95 V vs. reversible hydrogen electrode (RHE)), the NH₃ yield rate of 2.68 mmol h^-1 cm^-2 at -0.85 V versus RHE, and over 120 h of stable operation, outperforming previously reported Fe-based catalysts for NO₃RR. The desalination device achieves the highest salt removal rates (1326.92 µg cm^-2 min^-1) among various desalination methods. Ten cycles of natural seawater desalination to drinking water are demonstrated with 99% ion removal. This work presents an innovative solution for addressing sustainable water challenges.