The photocatalytic O-2 evolution from water oxidation was investigated over a series of WO3 materials treated with hydrogen at different temperatures. The activity of WO3 treated with hydrogen at 200 degrees C can be enhanced to 2.3 times of that of pristine WO3. The surface WO3 layer is partially reduced during the hydrogen treatment, forming a kind of HxWO3-WO3 composite material. The HxWO3 phase possesses high electrical conductivity and plays as a reduction cocatalyst for WO3 in the photocatalytic process. Formation of suitable amount of HxWO3 could facilitate the transfer of electrons, leading to efficient charge separation of WO3 and resulting in the enhancement of the photocatalytic O-2 evolution activity under visible light irradiation. Fabrication of semiconductor and conductor nanocomposite. might be a useful strategy for the development of efficient water-splitting photocatalysts. (C) 2013 Elsevier Inc. All rights reserved.