Development of a visible light photocatalyst is challenging. Herein, we report a significant activity enhancement of WO3 upon addition of CuWO4. Reaction was carried out under visible light for phenol degradation in aqueous suspension in the presence of H2O2. A maximum reaction rate was observed at 1.0 wt% CuWO4, which was 2.1 and 4.3 times those measured with WO3 and CuWO4, respectively. Similar results were also obtained from the photocatalytic formation of OH radicals, and from the electrochemical reduction of O-2. A possible mechanism responsible for the improved activity of WO3 is proposed, involving the electron transfer from CuWO4 to WO3, followed by the reduction of H2O2 over WO3. (C) 2016 Elsevier B.V. All rights reserved.