The design of efficient heterojunction photoanodes with appropriate band alignment and ease of charge separation has been one of the most highly focused research areas in photoelectrodes. This work demonstrates the fabrication of a photoanode comprised of CdS sensitized CoFe₂O₄@Fe₂O₃ hierarchical nanosphere arrays on a FTO glass substrate and its application in photoelectrochemical water splitting. The hierarchical hematite nanosphere arrays were grown on FTO substrates by a solvothermal approach. Impregnation of Co²⁺ was achieved by surfactant-assisted low-temperature solvothermal phase transformation and a dipping process followed by annealing to form a CoFe₂O₄@Fe₂O₃ heterojunction. The effect of pre-annealing of substrates before the second hydrothermal step on Co²⁺ impregnation was studied along with the choice of the solvent. The fabricated electrodes were further sensitized with CdS nanoplate-like structures by a hydrothermal method to form a Z-scheme-Type II ternary heterojunction. The photoelectrochemical properties of the electrodes were analysed by potential linear sweep voltammetry under simulated solar irradiation (AM 1.5G, 100 mW cm⁻²) with a 0.5 M Na₂S and 0.5 M Na₂SO₃ electrolyte. The highest ABPE% observed at 0.59 V (vs Ag/AgCl) was 0.86% for the photoanode comprised of CdS sensitized porous nanosphere arrays formed by solvothermal Co²⁺ impregnation along with pre-annealing. The fabricated electrodes showed low sheet and charge transfer resistance as observed from the EIS plot. The nanostructure morphology, crystal structure, and phase analysis were carried out using XRD, TEM, SEM and FESEM with EDAX. DFT calculations were carried out to unravel the underlying electronic structure and electron transport processes at the heterostructure interfaces. We hope to inspire more research on ordered heterostructures with superior charge transport properties, proper band alignment, enhanced light absorbance, and charge separation with this work. We also aim to focus on the effect of pre-annealing and solvent–surfactant pair selection on ion impregnation induced phase transformation in nanostructures.