The electrochemical reactions on a Zn anode and a Pt cathode in water at 25 degrees C and the growth of ZnO particles are investigated by x-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The solution pH, current, and weight of the anode were measured as a function of the voltage applied between the anode and cathode from 10 to 400 V. At voltages below 100 V the dissolution of Zn occurs on the anode, and above 100 V the formation of ZnO also takes place. The applied current generates OH- at the cathode. Initially, when the pH is lower, ZnO nano-sized particles are deposited on the cathode. When the pH of the water increases, Zn2+ combines with OH- to form spindle-like ZnO particles as long as 1 mu m.