Mo₂C@3D ultrathin macroporous carbon realizing efficient and stable nitrogen fixation

Abstract

Ammonia is a key feedstock of fertilizers for farming and convenient hydrogen carrier as an emerging clean fuel, but industrial ammonium production process, Haber-Bosch reaction, is an energy-intensive process, consuming 1%–2% of global energy and producing 3% global CO₂. Electrochemical nitrogen reduction reaction (NRR) is one of the most promising routes to realize highly efficient NH₃ production under ambient conditions. However, up to now, few precious-metal-free electrocatalysts with desirable catalytic performance have been explored. In this work, Mo₂C nanodots anchored on three-dimensional ultrathin macroporous carbon (Mo₂C@3DUM-C) framework is developed toward significantly enhanced nitrogen reduction reaction. Thanks to the special structural design of 3D ultrathin macroporous carbon and highly active and stable Mo₂C toward N₂ electrochemical reduction, the Mo₂C@3DUM-C framework exhibits a high Faradaic efficiency of 9.5% for NH₃ production at −0.20 V and the yield rate reaches 30.4 µg h⁻¹${\rm{m}}{{\rm{g}}_{{\rm{M}}{{\rm{0}}_{\rm{2}}}{\rm{C}}}}^{-1}$. Further electrochemical characterizations reveal the enhanced electron transfer and increased electrochemical surface area in the 3D macroporous carbon framework. Moreover, the Mo₂C@3DUM-C electrocatalysts hold high catalytic stability after long-term NRR test. The temperature-dependent yield rate of NH₃ demonstrates that the activation energy of nitrogen reduction on the employed catalyst was calculated to be 28.1 kJ mol⁻¹. Our proposed earth-abundant Mo₂C@3DUM-C demonstrates an alternative insight into developing efficient and stable nitrogen fixation catalysts in acids as alternatives to noble metal catalysts.