Herein, we synthesized porous Zn_1-xCd_xS nanosheets (PNS)/ZnO nanorod (NR) heterojunction photoanode via self-templated conversion using successively hydrothermal and Cd²⁺ ion exchange methods. Moreover, after conversion of ZnO to inorganic–organic hybrid ZnS-1,6-hexanediamine (HDA)_0.5nanosheets/ZnO NR material, Cd²⁺ ion exchange was conducted. It was confirmed from X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM) analyses that the inorganic–organic hybrid ZnS(HDA)_0.5 NS was transformed into Zn_1-xCd_xS PNS/ZnO NR heterojunction photoanode via the replacement of Zn²⁺ by Cd²⁺ ion. Zn_1-xCd_xS PNS/ZnO NR-160C3H heterojunction photoanode synthesized at 160 °C for 3 h showed the highest photocurrent density of 4.10 mA cm⁻² (vs. RHE) under 1.5 G illumination, which was 7.9 times higher than that of bare ZnO NR photoanode. The porous nanostructured morphology and larger surface area of Zn_1-xCd_xS PNS/ZnO NR heterojunction photoanode fabricated by Cd²⁺ ion exchange result in efficient light absorption and effective charge transfer pathway. The photoluminescence (PL) and time-resolved photoluminescence (TRPL) results show the shorter lifetime (37 ns) and reduced recombination in Zn_1-xCd_xS PNS/ZnO NR-160C3H heterojunction photoanode. During PEC analysis, the possible charge transfer mechanism in Zn_1-xCd_xS PNS/ZnO NR heterojunction photoanode was proposed. Surface passivated Zn_1-xCd_xS PNS/ZnO NR-160C3H photoanode shows improved photostability and exhibited 3.8 times higher H₂ evolution (161 μmol) than the Zn_1-xCd_xS PNS/ZnO NR-160C3H (42 μmol) photoelectrode at 0.9 V vs. RHE.