We systematically investigated the impact of reaction atmosphere on the Pt cocatalyst photodeposition and hydrogen evolution. A long induction period which is hardly found in close-system appears in the presence of oxygen, and is affected by the concentration of chloroplatinic acid. The Pt cocatalyst is metal state and contributes to the electronic states near Fermi level judging from the valence band X-ray photoelectron spectrum. The cocatalyst metal Pt will reduce the surface photovoltage signals due to the metal feature. The hydrogen evolution rate increased and reached a platform with increasing the Pt coverage on the surface of photocatalyst which is characterized by the Pt:Ti atomic ratio. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.