This paper reports the development of zinc oxide films electrodeposited at different potentials on tin-doped indium oxide substrates. The effect of deposition potential on ZnO microstructure, optical absorption, and photocatalytic activity for water splitting reaction were studied in detail. The films were potentiodynamically grown by applying different deposition potentials, such as -0.7, -0.8, and -0.9 V at constant temperature (70 degrees C) for 30 min. The pH of precursor solution was maintained around 6 during the electrodeposition process. X-ray diffraction study revealed the hexagonal wurtzite crystal structure of the ZnO. The field emission scanning electron microscopy (FESEM) demonstrated a significant variation in the microstructure with changing deposition potential. UV-Visible spectroscopy demonstrated a significant change in the optical band gap values for the ZnO films deposited at different deposition potentials. The highest photocatalytic activity of water splitting was recorded for the films deposited at -0.8 V under AM. 1.5 G solar light illumination.