Strategies to improve the catalytic activity of Fe-based catalysts for nitrogen reduction reaction.

Electrochemical ammonia synthesis from N 2 under mild condition is considered a promising strategy to store energy produced by renewable sources, but it is affected by the lack of efficient catalysts for nitrogen reduction. In this work Fe-based nanoparticles with different morphology are deposited on carbon cloth via drop-casting and chemical reduction. The catalyst activity has been evaluated by cyclic voltammetry and chronoamperometry, using a 0.01 M phosphate buffered electrolyte (PBS). The produced ammonia has been determined through the indophenol method. As effective strategy to improve the catalytic activity, the morphology and particle size have been optimized and an electrochemical activation procedure has been implemented. Activation increases the available active sites and is related to higher amount of oxygen vacancies and Fe+2/Fe+3 ratio. Catalysts with optimized morphology produce ammonia at −0.35 V vs RHE with yield of 26.44 μg mg cat −1h−1 and Faradaic efficiency of 20.4%, more than five times higher than without activation. [Display omitted] • Fe-based NPs are deposited by drop casting and chemical reduction on C-cloth substrates. • Particles morphology has been optimized. • The catalytic activity for Nitrogen electroreduction reaction was investigated. • A crucial role is played by the oxygen vacancies and by the Fe+2/Fe+3 ratio. • The ammonia yield with the optimized catalyst was 5 times higher than without optimization. [ABSTRACT FROM AUTHOR]