Solar-driven photocatalytic water splitting offers a sustainable pathway to produce green hydrogen, yet its practical application encounters several challenges including inefficient photocatalysts, sluggish water oxidation, severe reverse reactions and the necessity of separating produced hydrogen and oxygen gases. Herein, we design and develop a photocatalytic system composed of two separate reaction parts: a hydrogen evolution cell containing halide perovskite photocatalysts (MoSe₂-loaded CH(NH₂)₂PbBr_3-xI_x) and an oxygen evolution cell containing NiFe-layered double hydroxide modified BiVO₄ photocatalysts. These components are bridged by a I₃⁻/I⁻ redox couple to facilitate electron transfer, realizing efficient overall water splitting with a solar-to-hydrogen conversion efficiency of 2.47 ± 0.03%. Additionally, an outdoor scaled-up setup of 692.5 cm² achieves an average solar-to-hydrogen conversion efficiency of 1.21% during a week-long test under natural sunlight. By addressing major limitations inherent in conventional photocatalytic systems, such as the cooccurrence of hydrogen and oxygen in a single cell and the resultant severe reverse reactions from hydrogen and oxygen recombination, this work introduces an alternative concept for photocatalytic system design, which enhances both efficiency and practicality.