Role of WO3 Layers Electrodeposited on SnO2 Inverse Opal Skeletons in Photoelectrochemical Water Splitting

Abstract

Tin dioxide (SnO2) inverse opals (IOs) were developed by a spin-coating-assisted sol–gel process. The SnO2 IOs exhibited a pore size of ∼260 nm in the 370 nm sized polystyrene bead (PS) templates. Electrodes having a WO3 layer with a band gap (Eg) of 2.6 eV were electrodeposited on the SnO2 IOs under a constant potential (−0.47 VAg/AgCl), where the thickness of the WO3 layer depended on the applied charge amount for WO3 electrodeposition (200–800 mC/cm2). As a control sample, a pure WO3 IO film with the same thickness of ∼3.1 μm was also prepared by electrodeposition. The pore diameter of the SnO2 IO structure declined noticeably as the deposited charge amount of the WO3 layer increased from 200 to 800 mC/cm2, leading to eventual coverage of the SnO2 IO structure with the WO3 (800 mC/cm2) layer. Moreover, X-ray diffraction analysis indicated a steady increase of the signal intensity of the monoclinic WO3 planes as the deposited charge amount of the WO3 layer increased, indirectly indicating an increased l...