Electrocatalytic N-2 fixation has been considered a most promising approach for sustainably producing NH3 under ambient conditions. However, owing to the strong chemical inertness of N-2, it is highly desired to explore efficient electrocatalysts for improving the yield and selectivity of nitrogen reduction. Herein, CeO2 and Mo2C nanoparticles embedded simultaneously in reduced graphene oxide nanosheets (CeO2/Mo2C@rGO) are successfully fabricated for catalyzing N-2 fixation. The as-obtained CeO2/Mo2C@rGO catalyst shows superior catalytic performance with an NH3 yield of 22.3 mu g h(-1) mg(-1) and a faradaic efficiency (FE) of 12.7% at -0.3 V vs. the RHE, distinctly outperforming the undoped Ce counterpart of Mo2C@rGO. The experimental and DFT calculations reveal that the introduced Ce optimized the electronic structure, contributing to the improved NRR performance.