Recently, 2D semiconductor-based heterojunctions emerge as a focal point of intensive research owing to their unique properties, including efficient charge separation and large interface areas. Herein, Ni or Co-doped black phosphorus/molybdenum disulfide (BP/MoS2–Y (Y: Ni, Co)) heterojunctions fabricate for photocatalytic H2 evolution and electrochemical nitrite sensor. Compared to the BP/MoS2, the BP/MoS2–Ni and BP/MoS2–Co exhibit enhanced H2 performance, as 6.4139 mmol h−1 g−1 and 7.4282 mmol h−1 g−1, respectively, in the presence of Eosin-Y (λ ≥ 420 nm). Furthermore, BP/MoS2–Co applies as an electrocatalyst on a GCE for the electrochemical detection of nitrite. To optimize the nitrite sensing performance of BP/MoS2–Co, the effect of the pH, amount of material, scan rates, and other conditions study in detail. The BP/MoS2–Co displays a linear response within the range of 100–2000 μM with a detection limit of 4.1 μM for DPV. This work can offer an opportunity for hydrogen systems as well as electrochemical sensor applications.