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 mgMo2C-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 ofNH3 demonstrates that the activation energy of nitrogen reduction on the employed catalyst was calculated to be 28.1 kJ mol-1.Our proposed earthabundant Mo2C@3DUM-C demonstrates an alternative insight into developing efficient and stable nitrogen fixation catalysts in acids as altematives to noble metal catalysts.