(Invited) Advanced Components Development for Electrochemical Ammonia Synthesis

Abstract

Ammonia is an essential industrial chemical for agricultural fertilizer, medical intermediates, and energy storage. For fuel cell electric vehicle applications, it can be used as a fuel directly or as a means of hydrogen storage due to its high energy density in the liquid state. Conventional ammonia production using Haber-Bosch processes require high pressure and temperature, which is energy intensive. In addition, approximately 1.9 tons of carbon dioxide is released per ton of ammonia produced, because fossil fuels are used as the energy source in the ammonia industry. Meanwhile, renewable energy sources like solar and wind have significantly penetrated into the energy market in the past decade. During off-peak times, a large portion of this renewable energy cannot be utilized and an economically viable technology has to be used to store this surplus, “stranded” energy. The strong need to store off-peak renewable energy provides an unprecedented opportunity to utilize electrochemically synthesized ammonia as a means of accumulating hydrogen equivalents and stranded energy. Our work aims to design and implement advanced components (e.g. catalyst and membrane) to transform electrochemical synthesis of ammonia (EAS) 1-2 and to integrate this process with off-peak renewable energy. The reactants are nitrogen and water that are immediately available and abundant. Novel metal oxide and metal nitride catalysts for the nitrogen reduction reaction (NRR) have been designed and synthesized, which may boost the ammonia production rate by at least an order of magnitude; the developed catalyst can also effectively suppress competing hydrogen evolution reaction. Second, high temperature anion exchange polymer membrane and composite ceramics electrolyte have been explored to further enhance process stability and ammonia production rate; they also enable the EAS at a wide temperature range, from 80 ℃ to 350 ℃. Techno-economic analysis (TEA) of the EAS system integrated with renewable energy will be analyzed to evaluate the cost feasibility. Faradic efficiency and overall electrical efficiency in the context of capital cost and operations cost will also evaluated. Acknowledgement: ARPA-E REFUL Program under award # DE_AR000814 Reference: Marnellos, G., and M. Stoukides, “Ammonia synthesis at atmospheric pressure,” Science, 282(2), 98-100 (1998). Licht, S, Cui, B., Wang, B., Li, F-F, Lau, J., and Liu, S., “Ammonia syhthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3”, Science, 345, 637-640 (2014)