A conceptually new, metal‐free electrocatalyst, black phosphorus (BP) is presented, which is further downsized to quantum dots (QDs) for larger surface areas, and thus, more active sites than the bulk form. However, BP QDs are prone to agglomeration, which inevitably results in the loss of active sites. Besides, their poor conductivity is not favorable for charge transport during electrolysis. To solve these problems, an electrochemically active, electrically conductive matrix, black tin oxide (SnO2−x) nanotubes, is employed for the first time. Through facile self‐assembly, BP QDs are stably confined on the SnO2−x nanotubes due to Sn‐P coordination, resulting in a robust, double‐active electrocatalyst. Benefiting from their synergistic superiority, the BP@SnO2−x nanotubes deliver impressively high ammonia yield and Faradaic efficiency, which represent a successful attempt toward advanced hybrid electrocatalysts for ambient nitrogen fixation. Through facile self‐assembly, black phosphorus quantum dots are stably confined on SnO2−x nanotubes, which serve as an electrocatalytically active and electrically conductive matrix. Benefiting from their synergistic superiority, the two components result in a robust, double‐active electrocatalyst delivering impressively high ammonia yield and Faradaic efficiency.