AbstractZnO nanorods (NRs) were synthesized hydrothermally on a pre‐seeded graphene/nickel foam (NF) substrate. The effects of concentration on the photoelectrochemical (PEC) cell performance and hydrothermal reaction were studied. The field emission scanning electron microscopy images revealed that the precursor concentrations influenced the shape of the ZnO NRs on graphene/NF (ZGN). The X‐ray diffraction pattern for hexagonal wurtzite demonstrated strong orientation along the (002) direction. Notably, compared with the other concentrations, 0.04 M ZGN exhibited the highest photocurrent density, which was attributed to the optimal diameter and length of the rods for efficient light absorption. This research showed enhanced PEC performance, compared with existing literature, emphasizing the exceptional quality of the produced ZGN.