Highly-Selective Electrochemical Reduction of Dinitrogen to Ammonia at Ambient Temperature and Pressure

Qiang Zhang*, Xiaoyang Cui, Cheng Tang, Tsinghua University, China

15th Annual NH3 Fuel Conference, Pittsburgh, PA, October 31, 2018
NH3 Energy+ Topical Conference at the AIChE Annual Meeting

ABSTRACT

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, owing 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.

Read the abstract at the AIChE website.

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Qiang Zhang , Tsinghua University
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