Improved Charge Separation in WO(3)/CuWO(4) Composite Photoanodes for Photoelectrochemical Water Oxidation

Porous tungsten oxide/copper tungstate (WO(3)/CuWO(4)) composite thin films were fabricated via a facile in situ conversion method, with a polymer templating strategy. Copper nitrate (Cu(NO(3))(2)) solution with the copolymer surfactant Pluronic(®)F-127 (Sigma-Aldrich, St. Louis, MO, USA, generic name, poloxamer 407) was loaded onto WO(3) substrates by programmed dip coating, followed by heat treatment in air at 550 °C. The Cu(2+) reacted with the WO(3) substrate to form the CuWO(4) compound. The composite WO(3)/CuWO(4) thin films demonstrated improved photoelectrochemical (PEC) performance over WO(3) and CuWO(4) single phase photoanodes. The factors of light absorption and charge separation efficiency of the composite and two single phase films were investigated to understand the reasons for the PEC enhancement of WO(3)/CuWO(4) composite thin films. The photocurrent was generated from water splitting as confirmed by hydrogen and oxygen gas evolution, and Faradic efficiency was calculated based on the amount of H(2) produced. This work provides a low-cost and controllable method to prepare WO(3)-metal tungstate composite thin films, and also helps to deepen the understanding of charge transfer in WO(3)/CuWO(4) heterojunction.