High-Performance Ammonia Electrosynthesis from Nitrate in a NaOH-KOH-H₂O Ternary Electrolyte

A glut of dinitrogen-derived ammonia (NH₃) over the past century has resulted in a heavily imbalanced nitrogen cycle and consequently, the large-scale accumulation of reactive nitrogen such as nitrates in our ecosystems has led to detrimental environmental issues. Electrocatalytic upcycling of waste nitrogen back into NH₃ holds promise in mitigating these environmental impacts and reducing reliance on the energy-intensive Haber-Bosch process. Herein, we report a high-performance electrolyzer using an ultrahigh alkalinity electrolyte, NaOH-KOH-H₂O, for low-cost NH₃ electrosynthesis. At 3,000 mA/cm², the device with a Fe-Cu-Ni ternary catalyst achieves an unprecedented faradaic efficiency (FE) of 92.5±1.5 % under a low cell voltage of 3.83 V; whereas at 1,000 mA/cm², an FE of 96.5±4.8 % under a cell voltage of only 2.40 V was achieved. Techno-economic analysis revealed that our device cuts the levelized cost of ammonia electrosynthesis by ~40 % ($30.68 for Fe-Cu-Ni vs. $48.53 for Ni foam per kmol-NH₃). The NaOH-KOH-H₂O electrolyte together with the Fe-Cu-Ni ternary catalyst can enable the high-throughput nitrate-to-ammonia applications for affordable and scalable real-world wastewater treatments.