Electrochemical reduction of N2 to NH3 under ambient conditions may provide an alternative to the Haber−Bosch process for sustainable NH3 production, as the Haber-Bosch process relies on fossil fuels and is energy-intensive (consuming 1−2% of the global energy supply). However, the development of this process has been hindered by the lack of efficient catalysts for the N2 reduction reaction (N2RR) under ambient conditions, due to the barrier for N2 activation and the competing hydrogen evolution reaction (HER). Here, we report electroreduction of N2 to NH3 on an Fe/Fe oxide catalyst, which was prepared by in situ reduction of a pre-oxidized Fe foil in 0.1 M phosphate buffer solution (PBS). The resulting Fe/Fe3O4 catalyst shows greatly enhanced activity and selectivity for N2RR under ambient conditions than the original Fe foil, achieving a Faradaic efficiency of 8.29% for NH3 production at −0.3 V vs the reversible hydrogen electrode in the 0.1 M PBS electrolyte, which is around 120 times higher than that of the Fe foil. The high selectivity is enabled by an enhancement of the intrinsic (surface-area-normalized) N2RR activity as well as an effective suppression of the undesired HER. Comparative studies with Fe/Fe oxide samples derived at different pre-oxidation temperatures indicate that the N2RR activity is affected by Fe/Fe oxide ratio. Furthermore, the N2RR selectivity of the Fe/Fe3O4 catalyst is also superior to that of commercial Fe, Fe3O4, and Fe2O3 nanoparticles, providing new insights into the understanding and development of efficient, cost-effective electrocatalysts for ambient NH3 synthesis.

Electrochemical synthesis of ammonia on Fe/Fe oxide catalyst

2019 Spring National Meeting

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