The effects of electrolyte NaCl, a major component of natural seawater, on photocatalytic hydrogen evolution in the presence of electron donors over Pt/TiO2 have been investigated. The adsorption performance and surface reaction of electrolyte NaCl and the electron donors on TiO2 have been characterized by electrophoretic analysis and in situ attenuated total reflectance infrared spectroscopy. Under acidic condition Cl- ions are adsorbed on TiO2, while under neutral and basic condition Na+ ions are adsorbed on TiO2. In the case of ethanol as an electron donor, the activity of photocatalytic hydrogen evolution over Pt/TiO2 increases when concentration of NaCl < 0.10 mol L-1. while the activity decreases when the concentration > 0.10 mol L-1. At different pH values, the activity decreases in the order: basic > neutral > acidic. In the cases of formic acid and oxalic acid as electron donors, the activities decrease with increase of NaCl concentration. The Na+ ions can affect adsorption performance of ethanol on TiO2. Possible reaction mechanisms were discussed. (C) 2011 Elsevier B.V. All rights reserved.