Herein, an experimental and density functional theory (DFT) analysis of the composite g-C3N4/BiVO4 microflower photocatalysts are comprehensively discussed. A remarkable photoelectrocatalytic solar hydrogen production has been observed for the as-developed photocatalysts, with different loading amounts of g-C3N4 (0.1, 0.4, 0.8, and 1.2 wt ), using lake water without the addition of sacrificial reagents. The 0.8 wt g-C3N4/BiVO4 microflower photocatalyst evinced remarkable photoelectrocatalytic activity of 21.4 mmol/h of hydrogen generated in comparison to other samples with an AQE of 4.27 at 420 nm. In addition, the photocurrent density of 0.8 wt g-C3N4/BiVO4 microflower was 2-fold higher than that of pure BiVO4. This was attributed to its better crystallinity and optical properties, confirmed from XRD and DR-UV-vis analysis. The DFT analysis further corroborated that the efficient photocharge carrier separation and limited photocharge carrier recombination corresponded to the synergistic effect of the band offset and built-in electric field. Copyright © 2020 American Chemical Society.