(Invited) Green Ammonia Production from Electrochemically Upcycling Waste Nitrogen in an Membrane-Free Alkaline Electrolyzer

NH 3 is an essential nutrient for life, but its production through anthropogenic N 2 -fixing process has caused alarming damages to ecosystems and human health. Excessive NO 3 - leakage into water bodies due to overfertilization has led to the formation of "dead zones" in coastal areas. Denitrification generates N 2 O, which is 300 times more potent than CO 2 . Restoring the balance between the generation and elimination of Nr is an urgent task for humanity. Efforts to address the negative impact of human-generated N r have focused on converting it to harmless N 2 or improving its utilization in the nitrogen cycle. One promising method is electrochemical conversion, which can eliminate N r without additional oxidants/reductants. However, achieving selective NO3RR toward N 2 is challenging. An alternative approach is to convert other forms of N r to NH 3 in an electrochemical reactor, which could reduce the environmental impact of N r and decrease the NH 3 demand from the Haber-Bosch process, while also reducing the use of fossil-derived H 2 . In this work, we report our work on the development of a membrane-free alkaline electrolyzer (MFAEL), which transforms N r into NH 3 as the sole N-containing product. With the inexpensive and robust MFAEL system, we achieved an ampere-level partial current density towards NH 3 production. By properly choosing the conditions of NH 3 collection from MFAEL, continuous production of pure NH 3 -based chemicals can be realized without the need for additional separation procedures. Techno-economic analysis (TEA) suggests the potential economic feasibility of the waste-to-NH 3 process by coupling electrodialysis (ED) for Nr concentration and the MFAEL process for Nr conversion, offering an all-sustainable route for upcycling waste N into the highest-demanded N-based chemical product. Our recent efforts on green-ammonia capture CO 2 and reduction to valuable chemicals will also be briefly presented.