Electrochemical synthesis of ammonia directly from N2 and water over iron-based catalysts supported on activated carbonElectronic supplementary information (ESI) available. See DOI: 10.1039/c6gc02386j

• Main Authors: Cui, Baochen, Zhang, Jianhua, Liu, Shuzhi, Liu, Xianjun, Xiang, Wei, Liu, Longfei, Xin, Hongyu, Lefler, Matthew J, Licht, Stuart
• Format: Article
• Language: English
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/c6gc02386j

A new green methodology for the CO 2 -free synthesis of ammonia from air and water is presented. The conventional production of H 2 utilizes fossil fuels and causes a massive greenhouse gas release, making ammonia production one of the most energy intensive and highest CO 2 emitting manufacturing processes. In 2014 we introduced an alternative method for efficient ammonia synthesis that utilizes water (along with N 2 ) instead of H 2 based on electrolysis of nano-structured catalyst suspensions of Fe 2 O 3 in low temperature aqueous or higher temperature molten hydroxide electrolytes. Here, this is replaced with a solid Fe 2 O 3 catalyst confined to activated charcoal opening pathways to improve the rate and efficiency of ammonia production. Cyclovoltammetric studies show that Fe 2 O 3 /AC catalysts can inhibit competing hydrogen reduction and enhance reduction of iron. This iron-based catalyst supported on activated carbon (Fe 2 O 3 /AC) was prepared for use as an electrocatalyst for the electrochemical synthesis of ammonia in molten hydroxide (NaOH-KOH) directly from wet N 2 at atmospheric pressure. XRD analysis shows that the catalyst exhibits a Fe 2 O 3 structure. At 250 °C, a voltage of 1.55 V with a current density of 49 mA cm −2 yielded the highest rate of ammonia formation, 8.27 × 10 −9 mol (s cm 2 ) −1 . The highest coulombic efficiency for the 3e − per ammonia formation, 13.7%, was achieved at 1.15 V with a lower average current density of 11 mA cm −2 . This is a promising simple technology for the sustainable synthesis of ammonia in the future. A CO 2 -free electrosynthesis of ammonia from air and water is presented with a solid Fe 2 O 3 catalyst confined to activated charcoal.