Graphitic carbon nitride (g-C3N4) is one of the promising two-dimensional metal-free photocatalysts for solar water splitting. Regrettably, the fast electron-hole pair recombination of g-C3N4 reduces their photocatalytic water splitting efficiency. In this work, we have synthesized the CuO/g-C3N4 heterojunction via wet impregnation followed by a calcination method for photocatalytic H-2 production. The formation of CuO/g-C3N4 heterojunction was confirmed by XRD, UV-vis and PL studies. Notably, the formation of heterojunction not only improved the optical absorption towards visible region and also enhanced the carrier generation and separation as confirmed by PL and photocurrent studies. The photocatalytic H-2 production results revealed that CuO/g-C3N4 photocatalyst demonstrated the increased photocatalytic H-2 production rate than bare g-C3N4. The maximum H-2 production rate was obtained with 4 wt % CuO loaded g-C3N4 photocatalyst. Importantly, the rate of H-2 production was further improved by introducing simple redox couple Co2+/Co3+. Addition of Co2+ during photocatalytic H-2 production shuttled the photogenerated holes by a reversible conversion of Co2+ to Co3+ with accomplishing water oxidation. The effective shuttling of photogenerated holes decreased the election-hole pair recombination and thereby enhancing the photocatalytic H-2 production rate. It is worth to mention that the addition of Co2+ with 4 wt % CuO/g-C3N4 photocatalyst showed similar to 7.5 and similar to 2.0 folds enhanced photocatalytic H-2 production rate than bare g-C3N4/Co2+ and CuO/g-C3N4 photocatalysts. Thus, we strongly believe that the present simple redox couple mediated charge carrier separation without using noble metals may provide a new idea to reduce the recombination rate. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.