CdS is a semiconductor which can absorb visible light to generate electrons and holes. In urea solution, the holes are accepted by urea and oxidize urea while the electrons are accepted by water to reduce water to hydrogen. Photoluminescence of CdS QDs in urea showed lower amplitude as the quenching effect of urea on CdS QDs, which proves the holes transfer from CdS to urea. Photoelectrochemical test of TiO₂/CdS electrode in urea solution showed photocurrent generated by the oxidation of urea and reduction of water. The decrease of photocurrent with time is because of photocorrosion of CdS, which is self-oxidation of CdS by holes generated after illumination. A dielectric layer ZnS was deposited on CdS by successive ionic layer absorption and reaction (SILAR) to passivate the CdS surface, which improved the intensity and stability of photocurrent.