(707g) Direct Electrosynthesis of Ammonia from Nitrate Reduction Reaction Via Catalyst Design and Electrolyzer Engineering

Electrochemically converting nitrate ions, a widely distributed nitrogen source in industrial wastewater and polluted groundwater, into ammonia represents a sustainable route for both ammonia fuel synthesis and wastewater treatment. However, the reaction environments in current lab-scale tests are still far from practical conditions for generating ammonia from real wastewater. Here, we first report a high-performance Ru-dispersed Cu nanowire catalyst that delivers an industrial-relevant nitrate reduction current while maintaining a high NH₃ Faradaic efficiency. This high nitrate-reduction catalytic activity enables over a 99% nitrate conversion into ammonia while still maintaining an over 90% Faradaic efficiency. Next, we report a three-chamber solid electrolyte reactor design, and couple this with cation shielding effects for efficient nitrate reduction reaction without supporting electrolytes. By flowing treated nitrate-containing water from the cathode chamber to the middle solid electrolyte layer, we can realize a cation shuttling from the middle layer back into the cathode chamber to boost the nitrate reduction selectivity. This reactor system can deliver high ammonia Faradic efficiencies (> 90%) at practical current densities (> 100 mA cm^–2) under a typical wastewater nitrate concentration of 2,000 ppm, enabling a high-purity water effluent with no need for any electrolyte recovery processes.