(543c) Highly-Selective Electrochemical Reduction of Dinitrogen to Ammonia at Ambient Temperature and Pressure

Catalytic conversion of dinitrogen (N₂) into ammonia under ambient conditions represents one of the Holy Grails in catalysis and surface science. As a potential alternative to the Haber-Bosch process, electrochemical reduction of N₂ to NH₃ is attractive owing to its renewability and flexibility, as well as sustainability for producing and storing value-added chemicals from the abundant feedstock of water and nitrogen on earth. However, owning to the kinetically complex and energetically challenging N₂ reduction reaction (NRR) process, NRR electrocatalysts with high catalytic activity and high selectivity are rare. In this contribution, as a proof-of-concept, we demonstrate that both the NH₃ yield and NH₃ faradaic efficiency (FE) at ambient conditons can be improved by modification of the hematite nanostructure surface. The hematite electrocatalysts were fabricated with different numbers of surface oxygen vacancies. A higher concentration of surface oxygen vacancies renders improved performance toward NRR. A maximum ammonia production rate of 0.46 µg h^−1 cm^−2 and a maximun FE of 6.0% have been achieved at −0.9 V vs Ag/AgCl in 0.1 M KOH electrolyte. This is the highest FE reported so far among non-precious metal based catalysts using a polymer-electrolyte-membrane type cell and higher than those of the precious metal based catalysts (Ru/C and Pt/C) under comparable reaction conditions. This work suggests the important role of surface states in transition metal oxides for promoting electrocatalytic reduction of N₂ to NH₃ under ambient conditions and may spur interest toward rational structure design of efficient electrocatalysts for NRR with enhanced activity and selectivity.