(399h) Rational Design of Metal Electrocatalysts for Ambient Ammonia Synthesis

Electrochemical reduction of N₂ to NH₃ under ambient conditions may provide an alternative to the Haber−Bosch process for sustainable NH₃ synthesis and enable renewable energy storage in NH₃ as a carbon-neutral fuel when powered by solar- or wind-generated electricity. However, the development of such process has been impeded by the lack of efficient electrocatalysts for N₂ reduction reaction (N₂RR), due to the inertness of N₂ and the competing hydrogen evolution reaction (HER). Here we report ambient electroreduction of N₂ to NH₃ with a high selectivity on Pd and Fe-based catalysts. We found that Pd nanoparticles can catalyze the electrohydrogenation of N₂ to NH₃ in a phosphate buffer solution and exhibit a high yield rate and a Faradaic efficiency of 8.2% for NH₃ production at +0.1 V vs the reversible hydrogen electrode (RHE). The unique activity of Pd at low overpotentials outperforms other catalysts including Au and Pt, and is attributed to the in situ formed Pd hydride [1]. We also developed an Fe/Fe₃O₄ catalyst for electrochemical NH₃ synthesis, which was prepared by oxidizing an Fe foil at 300 ^oC in O₂ atmosphere followed by in situ electrochemical reduction until a stable state is reached. The derived Fe/Fe₃O₄ catalyst shows a Faradaic efficiency of 8.3% for NH₃ production at −0.3 V vs RHE, superior to the catalytic performance of Fe, Fe₃O₄, and Fe₂O₃ nanoparticles. The enhanced selectivities for N₂RR on the Pd and the Fe/Fe₃O₄ catalysts are both attributed to a large improvement of the N₂RR activity as well as an effective suppression of the HER activity.

References:

[1] Wang, J.; Yu, L.; Hu, L.; Chen, G.; Xin, H.; Feng, X. Ambient ammonia synthesis via palladium-catalyzed electrohydrogenation of dinitrogen at low overpotential. Nature Communications 2018, accepted.