(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 HaberâBosch 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 . 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 â0.3 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.
 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.