Large gold islands were deposited on n-TiO_2 single crystal electrode by sputtering, photo-reduction and electrodeposition. Photoelectrochemical behaviors of Au-coated semiconductorelectrode and pure Au electrode were measured in H_2SO_4 solution and acidic solution containingFe_(2+/3+). From the analysis of these polarization curves it was found that the contact between goldparticles and semiconductor surface is mainly ohmic in nature. The catalytic behaviors of gold is-lands on the competitive photo-oxidation of Ce_3+ and water were studied by using the RRDE withinterchangeable disc. It was proved that gold particles in the form of large islands could only catalysedark (electrochemical) reaction, but not the photo-electrochemical reaction. Large gold islands were deposited on n-TiO_2 single crystal electrode by sputtering, photo-reduction and electrodeposition. Photoelectrochemical behaviors of Au-coated semiconductorelectrode and pure Au electrode were measured in H_2SO_4 solution and acidic solution containing Fe_ (2 + / 3 +). the analysis of these polarization curves it was found that the contact between gold nanoparticles and semiconductor surfaces is mainly ohmic in nature. The catalytic behaviors of gold is-lands on the competitive photo-oxidation of Ce_3 + and water were studied by using the RRDE within interchangeable disc. It was verified that gold particles in the form of large islands could only catalysedark (electrochemical) reaction, but not the photo-electrochemical reaction.