BiVO(4 )is a considerably promising semiconductor for photoelectrochemical water splitting due to its stability, low cost and moderate band gap. In this research, g-C(3)N(4 )was proposed in Z-scheme configuration which boosted the performance of BiVO4 up to four times. The experimental observations were counterchecked with Density Functional Theory (DFT) simulations. A TiO2 /BiVO4 heterojunction was developed and its performance was compared with that of g-C3N4 /BiVO4. The photocurrent for g-C3N4/BiVO4 was 0.42 mAcm(-2) at 1.23 V vs. RHE which was the highest among g-C(3)N(4 )based Z-scheme heterojunction devices. Lower charge transfer resistance, higher light absorption and more oxygen vacancy sites were observed for the g-C3N4 based heterojunction. The simulated results attested that g-C3N4 and BiVO4 formed a van der Weals type heterojunction, where an internal electric field facilitated the separation of electron/hole pair at g-C-3 N-4/BiVO4 interface which further restrained the carrier recombination. Both the valence and conduction band edge positions of g-C3N4 and BiVO4 changed with the Fermi energy level. The resulted heterojunction had small effective masses of electrons (0.01 m(e)) and holes (0.10 m(e)) with ideal band edge positions where both CBM and VBM were well above and below the redox potential of water.