In this study, ZnO/Co₃O₄ composite thin-film room-temperature hydrogen (H₂) sensors were prepared via the hydrothermal method and self-assembly techniques. The test results show that the composite sensor with a layer assembly ratio of 1:1 has good sensing performance for H₂. The ZnO/Co₃O₄ composite sensor can detect a wide range of H₂ concentrations from 100 to 50,000 ppm, and the response toward 300 ppm H₂ is more than six-times that of a single nanomaterial. In addition, it has a faster response recovery speed, better repeatability, selectivity and long-term stability. The improvement in composite sensor performance results from the synergistic effect between ZnO and Co₃O₄ materials and the formation of heterostructures. The prepared ZnO/Co₃O₄ composite thin-film sensor was successfully applied to detect the H₂ production concentration and behavior of an electrolytic cell for hydrogen production by water electrolysis.