Ammonia is an important raw material in the fertilizer industry and a promising H-based fuel. However, its synthesis still largely relies on the conventional Haber-Bosch process, which is not only energy-consuming, but also environmentally damaging. Alternatively, the electrochemical synthesis of ammonia has drawn considerable interest. Herein, sandwich-like reduced graphene oxide/yolk-shell-structured Fe@Fe3O4/carbonized paper has been synthesized and employed as a freestanding electrode for nitrogen reduction reaction at room temperature and atmospheric pressure. The electrocatalytic measurements show that the as-obtained freestanding electrode exhibits high electrocatalytic activity (NH3 formation rate of 1.3 × 10-10 mol cm-2 s-1), excellent selectivity (faradaic efficiency of 6.25%), and good stability, which are equivalent to (or even higher than) those of previously reported noble metal-based catalysts under comparable reaction conditions. The superior electrocatalytic performance of the rGO/Fe@Fe3O4/CP freestanding cathode for electrochemical synthesis of ammonia is mainly attributed to its unique sandwich-like nanoarchitecture with the middle yolk-shell-structured Fe@Fe3O4 nanoparticles and the synergistic effect between rGO and Fe@Fe3O4.