We introduce the visible-light photocatalytic H2 evolution reaction as catalyzed by a cobaloxime/carbon nitride (C3N4) noble-metal-free hybrid photosystem by using a continuous-flow sampling reaction system. The photocatalytic H2 evolution rate is highly dependent on the structure of C3N4, in which porous C3N4 shows the best activity compared with bulk C3N4 (lamellar) and C3N4 nanosheets. When using porous C3N4, the system is neither affected by the solution pH, nor the C3N4 concentration, nor the structure of the cobaloxime complex.